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Healthy CropsHealthy CropsA New Agricultural Revolution

Online version of the printed 2004 edition, made available by The Gaia Foundation

FRANFRANCISCISCHABOUSSOCHABOUSSOUU

This English translation is dedicated to the memory ofJosé Lutzenberger (1926 - 2002),

father of the environmental movement of Brazil.

Healthy CropsA New Agricultural Revolution

FRANCIS CHABOUSSOU

Originally translated by Mark Sydenham, Grover Foley and Helena Paul

This online version of Healthy Crops: A New Agricultural Revolution has been reproduced by The Gaia Foundation

to resemble, as closely as possible, the 2004 English language edition of the book.

The English edition of Healthy Crops: A New Agricultural Revolution was first published in 2004 by

Jon Carpenter PublishingAlder House, Market Street, Charlbury OX7 3PH

for The Gaia FoundationPrinted in England by J.W. Arrowsmith Ltd., Bristol

ISBN 1 897766 89 0Printed in England by J.W.Arrowsmith Ltd., Bristol

In collaboration with:

Fundacao Gaiawww.fgaia.org.br

The Gaia Foundationwww.gaiafoundation.org

French edition [c] Flammarion, La Maison Rustique, Paris 1985English translation [c] The Gaia Foundation

The Gaia Foundation (Registered Charity no: 327412) holds the rights to the

English language translation of Healthy Crops: A New Agricultural Revolution.

This publication is for educational purposes and not for commercial purposes. Reproduction of this publication, in whole or part, for educational purposes is

permitted provided the source is fully acknowledged. This material may not be reproduced for sale or other commercial purposes.

Contents

Acknowledgements viiiCommentary 10Preface 1Introduction 7

PARTONEChapterI:ResurgenceofDiseaseandPest

DamageBroughtaboutbyPesticides

I. Seriousconcernsaboutcrophealth 13II. Chemicalpesticidesaredirectlyimplictedin

‘biologicalimbalances’ 15III. Conclusions 17

Chapter2:Plant-ParasiteRelations:theTrophobiosisTheory

I. Theinfluenceofenvironmentalfactorsontheresistanceofplants 19

II. Therelationshipsbetweenplantandparasites 31

Chapter3:TheRepercussionsofPesticidesonthePhysiologyof Plants,andtheConsequencesfortheirResistancetoParasites

I. Theparticipationofpesticidesinthemetabolismofthehostplant 38II. Pesticidalpenetrationintotheplant 39III. Therepercussionsofgrowthsubstances 42IV. Theeffectsofchlorinatedchemicals,especiallyDDT 51V. Sideeffectsoforganophosphates 54VI. Theeffectsofcarbamatesanddithiocarbamates 56VII. Theeffectsofotherpesticides:newfungicidesandherbicides 58VIII.Conclusions 59

vi Healthy Crops

PARTTWO

Chapter4:TheFailuresofChemicalPesticidesinArboricultureandViticulture:BacterialDiseaseandPlantPhysiology

I. Similarityofphytosanitaryproblemsinarboricultureand viticulture 63II. Theexacerbationofparasiteactivity:‘resistance’ormultiplication?64III. Bacterialdiseaseandthephysiologyoftheplant 65IV. Themechanismofeffectsofdifferentenvironmentalfactorsonthe

developmentofbacterialdiseases.Importanceoflevelsofsolublenitrogenintissues 69

V. Controlofbacterialdiseasesinvolvestakingintoaccountthenutritionalrelationshipsbetweenbacteriaandthehostplant.Developmentofbacterialdiseasesandthenatureoftherelationsbetweenplantandbacteria 73

VI. Theeffectsofchemicalpesticidesintheplant-parasiterelationship 74VII. Conclusions:newprospectsofcontrol 79

Chapter5:PlantsandViralDiseases

I. Environmentalfactorsandviraldiseases 83II. Inorganicfertilisationandthevirulenceofthevirus 85III. Organicfertilisationandviraldiseases 98IV. Repercussionsofpesticidesonviraldiseases 102V. Graftingandviraldiseases.CaseStudy:thegrapevine 105VI. TheworksofVagoandtheconceptofdisease 108

Chapter6:RelationsBetweenViralDiseases,Vectors(Aphids)andPesticides

I. Whatmakesviraldiseasesexceptional? 114II. Chemicalcontrolofvectors 115III. Thecomplexityoftherelationsbetweenviraldiseases,vectors

(aphids),andpesticides 125IV. Conclusions 130

vii Contents

Chapter7:TheImpactsofGraftingontheScion’sresistance

I. ObjectivesandConsequencesofGrafting 131II. Theseverityofdiseasesofthevineyardinrelationtoits

reconstructionthroughgrafting 132III. ThephysiologyofVitis ripariaandofcertain‘composites’ofRiparia

andscion 133IV. Rootstock-inducedresistanceinthescion 142V. Graftingandthequalityoftheproduct 144

PARTTHREE

Chapter8:StateofHealthinRelationtotheMethodofCultivation

I. ‘Intensive’cultivationofcerealcropsandthexxplosionofso-called‘diseasesofprogress’ 147

II. Thestateofhealthofcerealsusingtraditionaltechniques:‘organicagriculture’ 158

III. Ricegrowing:healthproblemsandtheresultsofabalanced fertilisation 161

Chapter9:CorrectionofDeficienciesandStimulationofProteinSynthesistoPreventandControlofDiseasesandParasites

I. Introduction 172II. Cationicbalancesandthenutritionoftheplant 173III. Deficienciesandviraldiseaseinthetomato 180IV. Onthemodeofactionofvariousanti-fungalproducts 180V. Boroninplantphysiologyandresistance 185VI. Isitpossibletocontrolfruitscabbynutritionaltreatments? 193VII. Theimmunityoftheplantachievedbynutritionaltreatments 198

GeneralConclusions 205

Bibliography 210

viii Healthy Crops

Acknowledgements

JOSÉ LUTZENBERGER WAS PASSIONATE about this book. HebelievedthatitwasvitalthatitshouldappearinEnglish,inordertocounterthepowerful pesticides lobby throughout theEnglish-speakingworld andprovideaclearcaseforpoison-freeagriculture.

JoséLutzenbergerbeganasanagronomistworkingforthechemicalgiantBASFinGermany.In1972hedecidedtoleavehisjobandreturntoBrazilafterobservingthe terribleenvironmental impactofpesticidesused ingrowingriceinhishomestateofRioGrandedoSul.Hebecameatirelessopponentofpesticideuseandadvocateofwhathecalled‘regenerativeagriculture’,asanalternativetotherelentlessindustrialisationoffarmingandtheenviron-mentaldegradationitcauses.Hebasedhismethodsonhiscarefulobserva-tionofecologicalprocesses,andbelievedthatanunderstandingofecologicalprinciples freespeople toactbecause they learntowork ‘indialoguewithnature’.HehimselfhadlittletimeforwritingamidsttheconstantrequestsforhisassistanceandinspirationfromalloverBrazilandbeyond,butmuchoftheworkthathewascarryingoutandadvocatingthroughouttheworldwasapracticalapplicationoftheargumentofthisbook.ItisagreatpitythathedidnotlivetoseethebookpublishedinEnglish,butwithouthispersistenceitwouldnothavehappened.

Lutzenberger’s daughters Lilly and Lara continue his work throughthe environmental organisation Fundacao Gaia and the ocmpany VidaDesenvolvimiento Ecológico, both located in Porto Alegre-RS, Brazil.The company focuses on industrialwastemanagement and recycling andFundacaoGaia receives people from all over theworld to experience theapplication of regenerative agriculture and environmental restoration intransforminganabandonedquarryintoabeautifulanddiverseplace.

TheGaiaFoundationwouldliketothankEdwardGoldsmithandEdwardPosey for their personal commitment to the project, which has taken anumberofyearstocomplete.Wearedeeplyindebtedtothe

ix Acknowledgements

FoundationSauveforprovidingthefundsrequiredtopublishthebook.WewouldliketothankUlrichLoeningforhisadviceandhiscommentaryforthebookandHelenaPaulwhodedicatedherselftoensuringthatChaboussou’smessageisatlastaccessibleinEnglish.

10 Healthy Crops

Commentary

byDrUlrichELoening,biochemistandEmeritusDirector,CentreforHumanEcology,UniversityofEdinburgh

CHABBOUSSOUHASDISCOVEREDamajornewgeneralisation: byreviewing innumerablestudiesstretchingovernearly50years,hedemon-stratedthat thenutritionalstateofcropplantsaffect theirsusceptibility topestsanddiseases.Likesomanyinnovativeideasinbiology,thisworkopensmanynewavenuesandexpandsthehorizonwithnewunknowns.

The theory thathedeveloped from theseobservations,whichhe calledTrophobiosis is a commonsense and essentially simple biochemical argu-ment:thatmostpestanddiseaseorganismsdependfortheirgrowthonfreeamino acids and reducing sugars in solution in theplant’s cell sap.Everyfarmer has experienced the increase in diseases after heavy fertilisationwithnitrogen;theGreenRevolutionvarietiesaregoodexamplesinwhichrichfertilisationcreatessusceptibilitytopests,requiringmorepesticidestocontrol.Chaboussouexplainswhy.

Almostallconventionalchemicalagriculturaltechnologiescreatefavour-able conditions for the growth of pest and disease organisms: this bookshows how much of the problem can be explained through increases insoluble nitrogen, amino-acid and sugar concentrations in the plant cells.Forexample,heavyapplicationsofsolublenitrogenfertilisers increase thecellular amounts of nitrate, ammonia and amino acids faster than can beusedforthesynthesisofprotein.Similarlyherbicides,eveninrecommendedconcentrations, inevitably affect the crop plant somewhat (perhaps notvisibly), themain effectbeing a temporary reduction inprotein synthesis-themostsensitiveofmetabolicprocesses.Sprayingwithalmostanypesti-cideorfungicidehasthesameeffect.Thesereductionsintherateofproteinsynthesisresultintemporaryaccumulationofaminoacids.Therefore,whilethe immediateattackbyapestmaybereducedbyapesticide, thesuscep-tibility of the crop is increased:whenoffered soluble freenutrients, pestsgrowbetterandmultiplyfaster.Inthissensetherefore,agro-chemicalsandpoisonscausepestsanddiseases.

11

This conclusion suggests that pest and disease organisms cannot useprotein and polysaccharides directly and require soluble amino acids ansugars for growth.Lutzenbergeroftenargued that the various insects andevenfungalpestslackproteolyticenzymes,(asimpliedinhisintroductionaboutleaf-cutterants)butmanyinsectsandfungiandotherorganismsdoin fact have them. Chaboussou’s empirical evidence clearly demonstratesthat pestsanddiseaseorganismsgrowandmultiplyfasterwhentheplantcontainsmoresoluble freenutrients. Inotherwords, thebiochemicalandphysiologicalstateoftheplantisstronglyaffectedbythemethodsofculti-vation,andthiscontrolswhetherpestscaninvade:onecanavoidpestsanddiseasesthereforebymethodsofcultivationthatlimittheamountsofsolublenutrientsintheplant.

However, this important finding has been neglected. For example, aRoyalSocietySymposiumontheBiologicalControlofPestsandDiseases(1987)heldsoonafterChaboussou’sbookwaspublishedinFrench,madenomentionofthephysiologicalorbiochemicalstateoftheplantasafactorinsusceptibilitytopestsanddisease.Inotherwords,theideathatplantsprac-ticetheirown“IntegratedPestManagement”isnotpartofmodernthinking;yet thisprovidesaway forwardwhich isnothing less than“anagronomicrevolution.”

Ofcoursethereareotherconditions,suchasstress,drought,ageing,whichsimilarlyincreasesusceptibility.Goodhusbandryhasalwaystriedtomini-mise these. The balance ofmicronutrients is also important.Chaboussoubrings these intohis studies, includingalsomuchcircumstantial evidencefromtrialsdesignedforotherpurposes,aswellasdirectdatathatlinksonsetofdiseasewithreductioninproteinsynthesis.

ItisclearthatmuchneedstobedonetoestablishthevalidityofChaboussou’sinterpretations, by directmeasurement of amino acid and reducing sugarpools under different cultivation regimes, correlated with infection orsusceptibility.Fewsuchdirecttrialshavebeendone;itisagreatpitythattheextensivetrialsoftheBoxworthProjectnearCambridge,England,fundedbytheMinistryofAgriculture,FisheriesandFoodfrom1982to1988,didnotaddressthesequestions.

xii Healthy Crops

Thepurposes of the projectwere to determine the ecological effects ofdifferent pesticide treatment regimes, the effects on crop yield and theidentification of practical management problems that arise, such as fromminimalpesticidetreatments.Verysmallchangesinthedesignofthesetrialswouldhaveallowedcorrelationstobemade,whichmightsupportordenyChaboussou’sinterpretations.Unfortunatelyitisnotpossibletoextracttherelevantdata,eitherfromthereportsorfromtheoriginalmaterial.

Thisbookthereforeopensafreshfieldforstudyanddevelopmentofagri-culturalpractices.Examplescouldinclude:a)otherthanthereducingsugarsandaminoacids,theremustbemanyrelatedfactorsthatchangeaccordingtotreatmentofthecrop;afewarementioned,butthescopefordiscoveryofothersandadeeperunderstandingiswideopen;b)onlyastarthasbeenmadeinthecomplexinterplayofthemicronutrients(ortraceelements);c)inparticularChaboussoushowshowthesymptomsofviraldiseasesrelatetothoseofmicronutrientimbalances,andcorrectionofthelatterminimisesthe effectsof the viruses;d)whichof themanypests, fungi andbacteria,dependsostronglyonsolublenutrients?Andarethereotherfactorsofplantnutrientimbalancesthatcanincreasesusceptibility?e)onemightnowadaysask whether the new herbicide-resistant genetically engineered crops aresimilarlyaffectedbyherbicide:therearealreadyreportsofincreasedfungalinfectionsinthese;f)Lutzenbergermentionedinhispreface,anumberofsubstancesthatseemtopreventpestsanddiseases;dotheseworkbyhelpingtheplantreduceitsinternalconcentrationsofsolublenutrients?g)andthenonehas thebigchallenge: couldonegrow theGreenRevolutionvarietiesunderconditionsthatinplaceofincreasedsusceptibility,promoteresistancetopestsanddiseases?Thesearesomeofthechallengesthatshouldreceivehighpriorityforresearch.

Whateverthetechnicaldetails,itisnowobviousthatcloseattentiontothephysiologicalandbiochemicalstatesofcropplantsmustbecomeavitalpartofagriculturalpractice.Suchanapproachconstitutesanewbiotechnologyinatruemeaningofthisterm.Thereismuchtobedone;Chaboussouhasprovidedapowerfulbasis.

1

Preface

byJ.A.Lutzenberger

BRAZILIANFARMERSANDGARDENERShaveasaying:‘EitherBrazileliminates the Saúva (the leaf-cutting ant, Ata) or the ant finishes Brazil’.Thisproverbcannotpossiblybetrue,orBrazilandmostofSouthAmericawouldhavebecomeabarrendesertlongbeforewehumansevenemerged.ThemanyspeciesofAtacameuponanefficientformofgardeningmillionsofyearsbeforetherewerehumanstoeventhinkofagriculture.Insidetheircavesintheground,theymakeakindofcompostfrompiecesofleavescutfromtrees,shrubs,herbsorgrassesandtheantsthemselvesfeedonthefruitbodiesofamouldtheygrowonthiscompost.Theyareincrediblyefficientincollectingtheleafmaterial.Abigtreecanbeleftbareovernightorawholeplantationdestroyed.

Theleaf-cuttingantisnotonlyveryefficientinitswork,itishardlyselec-tiveintheplantsitattacks.Thespeciesthatitshunscanbecountedonthefingersofahand.I’veseenitcutfloatingwater-plants,whereaccessible.Italsohasatremendouspotentialforreproduction.Whenthewingedmalesandfemalesflyouttomate,usuallybeforeastorm,thefuturequeenscarrywiththemthesporesoftheirspecies-specificmould.Soeachoneisequippedto start anewcolony.There aremany thousandsof them in eachnuptialflight.Ant colonies, like a people, are immortal, unless there is genocide.Inmygarden there is a colony that Ihaveknownandobserved sincemychildhood.Sometimesitisbigandcausesgreatdamage,thenitmayshrinkagain;italmostvanishes,butneverdisappears.Sohowcometheleaf-cuttingantshavenotstrippedBrazilofeverythinggreen?Andwhy,inaprefaceforChaboussou,doImentionacreaturethatheknewonlyfrombooks?

Ihadtheprivilegetoknowhimpersonally.Hedied,inl985,unexpectedly,ofaheartailment.Hehadbeenverypessimisticanddepressed.Asanimpor-tantresearcherinINRA,theFrenchofficialagriculturalresearchinstitution,hewasundergreatpressurefromtheinterestsoftheagrochemicalindustry.Theydidnotlikewhathehaddiscovered.

2 Healthy Crops

WhenIlastvisitedhim,onhispersonalfarmintheregionofBordeaux,wedidnotdiscussleaf-cuttingants.WewalkedmostlyinvineyardsandtalkedabouttheproblemsofEuropeancrops.But,evenwhiletalkingaboutgrapes,hegaveme theanswer to thequestionofwhy the leaf-cuttinganthasnotrazedallthatisgreeninSouthAmerica.

Tomy knowledge Chaboussou was the first researcher to put order intheobservationsofdozensofotherworkersinagriculturalplantpathology,includinghisown.Hewasthefirsttoshowthatpests,suchasinsects,mites,nematodes andpathogenic agents, suchasbacteria, fungi andevenvirus,onlycausedamageonplantsthataresomehowunbalancedintheirmetab-olismandhegaveusaworkingexplanationofthebiochemicalmechanism.HistheoryofTrophobiosisisarevolutioninplantpathologyandisamortalblowtoagro-chemistryascommonlypracticedinmodernagriculture.Butthechemicalindustryandtheschools,researchandagriculturalextensionthatithasbeenabletocoopt,donoteventrytorefutehim.I’veheardaguyon their side say: ‘Wewill not even ignorehim’.Unfortunately,with veryfewexceptions,Chaboussouisstillunknowntomostworkersinagriculture,eveninorganicagriculture.

The theory of Trophobiosis has to do with how plant nutrition affectsplanthealth,withwhatmakesaplantsusceptibleorresistanttodiseaseandto pest attack. Prevailing plant protection practices rest on the postulate,mostlyunspokenbutalmostuniversallyaccepted,evenamongmanyorganicfarmers,thatpests,suchasaphids,thrips,caterpillars,scales,mites,nema-todesandothers;pathogenicagentssuchasfungi,bacteriaandevenvirus,arearbitraryenemiesthat,whenpresent,willfuriouslyattackourcropsandwillonlystopwhenthereisnothingleft.ThatisthephilosophybehindthesayingwithwhichIbegan.Sowehavetofightthem,eradicatethemifpossible,orkeepthemincheckwithourmostefficientandpotentweapons.Themostaggressiveweapons at ourdisposal are the synthetic chemicalpoisons, orpesticides,asthechemicalindustrylikestocallthem.Buteveryfarmerwhoobserveshiscropsandenvironmentcarefully,knowsthatthesecreaturesarenotarbitraryinthewaytheyharmourplantationsandgardensandthat,themorepoisonsweapply,themorediseasesandpestsweget.

3 Preface

Forpeoplenot familiarwithmodernplantprotectionmethods in agri-culture, Chaboussou’s book – with all the technical and brand names ofpesticides,aswell asLatinnamesof insects, fungi,bacteria, etc. -mayberather difficult to read. For me, as an agronomist, familiar with modernagro-chemistry, itwas fascinating, I read it in twonights.Hereviewsandinterpretsdozensofotherresearchers’observationsandexperimentsandisoftenrepetitivetomakemattersasclearaspossible.Butitisaveryimportantreferencebookandeveryagronomistshouldhaveitonhisdesk.ThatiswhyIinsistedthatweneedagoodEnglishlanguageversionofit.WealreadyhavegoodGermanandBrazilianeditions.Thankstomyfriend,ourgreatecologyguruTeddyGoldsmith,wecannowpresentthisedition.IhopewecannowmaketheTheoryofTrophobiosisknownandappliedintheEnglish-speakingworld.Toomuchtimehasalreadybeenlost.

Forthosewhowillnotreadthewholebookbutwilluse itasaworkofreference,Iwilltrytoexplainitinaverysuccinctway:

A healthy plant, a plant in metabolic balance, is either in repose, forexampleinhibernationor,indryclimates,inestivation,oritisgrowingasvigorouslyasitcan,dependingonthesupplyofnutrients,waterandweather.Whenaplantisinreposethesapispoorinamino-acids;theywereusedupwhenpreparingfortheperiodofquiet.Whenitisgrowingvigorouslythesapisalsopoorinamino-acids.Intensiveproteo-synthesisusesuptheamino-acidsproducedinthecellasfastastheyappear.Inbothcasestheplantisnotnutritious for itsparasites.Theymay justbe able to survive,but theycannotthrive.Theyneedaveryhighlevelofsolublefood:notonlyamino-acids,tobuildtheirownproteins,butalsosugars,thesourcesofenergyforthe synthesis of proteins, andmineral nutrients to help build theirmorecomplicatedproteins,suchastheenzymes.Otherimportantingredientsarethenucleotides,thepiecesofthegeneticcode.Plantsthatarenotnutritiousforthepestsarealsonotpalatabletothem,theparasitesignorethem.Astowhichparticularpestorparasitewillthrive,thisdependsontheproportionofthedifferentingredients.

4 Healthy Crops

We mentioned above that the leaf-cutting ant is not very selectiveconcerningthespeciesitattacks,butwhenweobserveitcarefully-somethingmostmodernagronomistsdon‘tdo;theysimplyhurryfortheinsecticideassoonastheyseetheant–wecannothelpnoticingthatitisveryselectiveastotheindividualplantsofanyspeciesthatitdemolishes.Sometimestheantwillonlyworkonpartofaplant,nottouchingtherest,sometimesitwilllimititsattacktoacertainperiodonlyandthenloseinterest.

So,whenisaplantnutritiousforpestsanddiseasecausingbacteria,fungiand virus? When does it have an excessive level of amino-acids, sugars,nucleotidesandminerals?

Thewaywemanageourcropsinmodernagriculturemeanswefrequentlycausetheplanttobemetabolicallyunbalanced.Oneofthemostfundamentalchanges compared to traditional peasant agriculture is the downpour ofpoisons.Withveryfewexceptions,whatthechemicalindustrycallspesticides(insecticides,fungicides,herbicidesandafewothers)arebiocides.Theyaresubstancesthatharmlivingbeings.Eventhosethataresupposedtoactonlyonthesurfaceoftheplant,always,tosomeextent,penetrateintothelivingcell.Harmmaybe slight, but itmaymean inhibitionofproteo-synthesis,thereforecausingabuild-upofthesolublenutrientstheparasitesneed.Let’sillustratewithametaphor:averysmallandmomentarybottleneckononeofthelanesofabigexpresswaycancauseenormouscongestion.Beyondthecongestion,trafficlooksnormal.So,myplantmayseemtobegrowingquitenormally,but there isacongestionofamino-acids inthesap.Thiscan,ofcourse,beverifiedbyanalysis,suchasthatcarriedoutbyChaboussouandothers.

Another cause of inhibition is the way we treat our soils. Intensivemechanicalaggression,deepploughing,disking,frequentharrowingtokeepthe soil asnakedaspossible,destroys soilmicro-life.Ahealthy soil life isfundamentalforabalanceduptakeofmineralnutrients,especiallyoftraceelements. Deficiency in trace elements also causes inhibition in proteinsynthesis,thereforeabuild-upofnutrientsfortheparasite.

Excessinamino-acidsinthesapcanalsoresultwhenweforcetheplanttoproducemorethanitneeds,forinstance,withhighapplicationsofammoniafertilizers.

5 Preface

Inhibitioncanalsobecausedbyadverseweather,suchasdrought,suddenheatorcoldwaves.OnthepropertyofFundaçãoGaia,inaspellofunusualweather(somethingwearegettingevermorefrequently)aratherlongspellofwarm,dampdayswasfollowedbyasuddenheatwaveanddrought.Duringthistimeaglobularcactus,Notocactusottonis,thatisendemictotheregion,thereforewelladapted,wastotallydemolishedbytheant,somethingwehadneverseenbefore.Onlythethornswereleft.

ManyyearsbeforeImetChaboussou-Iwasstillworkingforamultina-tionalagro-chemicalcorporation,butIhadintensivecontactwithorganicfarming - I knew that pests shunned healthy plants, as most observantorganicfarmersknew.ButIdidn’tknowhowandwhy.Chaboussouwasarevelationtome.Eversince,inmyworkwithcrops,ingardensandinintactnature,Iseetrophobiosisconfirmed.Whateverdisturbsaplant’smetabolism-mechanicalorchemicalaggression,climateshock,destructionofsoillife-maymakeitsusceptibletoattackbypestsandtodisease.

Butwhy does Ata, our leaf-cutting ant, also choose unbalanced plants,whenitdoesn’teatthembutturnsthemintosomethinglikeacompostforitsmould to grown on?We know themould has no proteolitic enzymes.Somehowtheantalsoknowsitandfindsappropriateplantsforthemould.LikealltheotherpeststhatIhavebeenabletoobserve,theantidentifiestherightplantsfromadistance.

When we start harvesting cabbages in our vegetable garden, healthycabbagesthathadnopestattackorfungusdisease,andweleavetheouter,partially rotten leaves on the ground, it often happens that Saúva buildsitsroad,comingfrombeyondthefenceofthegarden–theyarealsogreatengineers,andmakebeautifulroads,oftendozensofyardslong,radiatingoutfromthenesttowheretheydetectaharvest–andstartharvestingthematerialonthegroundwithouttouchingtheremaininghealthyplants.Ofcourse,thecutleavesarebeginningtorot,withproteolysispredominatingoverproteosynthesis.

Theremustbesomeemanationfromthemetabolicallyunbalancedplants.Iwonderwhetheranybodyhasdoneresearchonthismatter.

6 Healthy Crops

I dare say that Chaboussou’s work is the most important discovery inagriculturalchemistrysinceLiebig.Itisafundamentalnewinstrumentforahealthy,clean,regenerativeandsustainableagriculture.Thesolutionliesnot in fighting arbitrary,wicked enemies of our crops, but in developingmethodsofkeepingourplantshealthy.AlloverBrazilwehavealreadyhadgreatsuccesswhenwesubstitutedconventionalpesticideswithstimulatingapplications,suchaswhey,cow’surine,maturebiogasslurry,groundrockrichintraceele-mentsandmanyothertreatmentsthatthefarmercanpreparehimself.Butthisisasubjectformanyotherbooks.

IreallyhopethatbymakingChaboussouknownintheEnglishspeakingworld,especially inthesocalledThirdWorld,wecanmakeanimportantcontribution to thefight against theuprootingof thepeasantby the agri-culturalpoliciesoftransnationalcorporations.HowsadChaboussouisnolongeramongus.

December2000

7 Introduction

Introduction

WEWILLBEGINwithabriefsummaryoftheargument.

Thefirstofthebook’sthreepartsisentitled:

‘Pesticides and Biological Imbalances’

Thefirstchapterdrawsattentionto theresponsibilityofchemicalpesti-cides for the resurgence of diseases and pests. These are not just old ortraditionalafflictionsbutalsonewpathogenicagentsthathaveattainedtherankofpests.Amongthemarethepsyllids,mites,numerouscerealdiseases(includingviralones),witheringdiseases,andtheviraldiseasesoffruittreesandthegrapevine.

Such‘biologicalimbalances’donotarisemerelyfromtheallegeddestruc-tion of ‘natural enemies’ but, rather, from disturbances of the nutritional environment-thatistosay,thebiochemicalstateoftheplantisalteredbytheintrusionofnewchemicalpesticides.

Thebasicconclusionis:the relations between plant and parasite are above all nutritional in nature.Thisisthetheoryoftrophobiosis. Itcastsdoubtonanalternativetheory:thattheresistanceofplantsisbasedonthepossiblepresenceofsubstances(phytoalexines)thataretoxicorrepellenttoparasites.Thetrophobiosistheorycontends,instead,thatplantsaremadeimmunetotheextentthattheylackthenutritionalfactorsthatparasitesrequirefortheirdevelopment. In short,what is involved is a deterrent effect, not a toxicaction.

Moreover,ourtheoryseemstoagreewiththenatureofrelationsbetweenplantandparasite.Theserelationsaredeterminedbyvariousenvironmentalfactors such as, for example,genetic factors (varietal resistance), the phys-iological cycle of the plant (suchasthestateofflowering),photoperiodism, climate, nature of the soil, fertilisation, nature of the stock and, finally, the effect of pesticides on the plant’s physiology.

Resistanceandsusceptibilitydependonthelevelofsolublesubstances.Astatewhereproteolysispredominatesislinkedtodisease,whilethepredom-inanceofproteinsynthesiscorrelateswithresistance.

8 Healthy Crops

Current developments in pests and diseases stem fromwhat are called‘intensive’agriculturalpractices.Thistermisappliedtothemisguidedutili-sationofchemicalpesticidesandfertilisers,particularlynitrogenfertilisers,whichleadstoinhibitionofproteinsynthesis.

However, certain findings indicate that the initial mechanism of thissusceptibility topesticidesmay lie in the creationof variousdeficiencies.Thereforeweentitlethesecondpartofourwork:

‘Deficiencies and Parasitic Diseases’

This secondpartconsistsof fourchapters, twoofwhicharedevoted toviraldiseases.Wehavetriedtoanalysetheeffectsofenvironmentalfactorson the development of these disorders and have found that they are notresponsibleforthedifferentreactionsofthevariousviraldiseaseswehavereviewed.What is crucial is thephysiological stateof theplant,while theimpactsofcontagionandvectorsseemtobeonlysecondary.Thisconclusionmeans thatwe shouldprobably changeour techniquesofdisease control,aboveallifonealsoconsiderstheindirecteffectsofpesticidesontheplantbeingprotected.

It is clearly no accident that the symptoms of viral disease are easily‘confused’withthesymptomsofdeficiencies.Thesedeficienciesarethetruecauseofthedisease.Thisalsoholdstrueforbacterialdiseases.The shift from strictly mineral products like copper and sulphur to chemical pesticides couldexplaintherecentandatfirstsightinexplicableoutbreaksofvariousdiseases,particularlybacterialandviralones.Chemicalpesticideshaveanoppositeinfluenceonthephysiologyofplantsfromthemineralones.

We also thought it indispensable to dedicate one section to the workofConstantinVago.Vago’s research suggests theremight be a general lawapplyingtoboththeanimalandtheplantkingdoms,thatwouldexplainthephenomenonof‘disease’inthesamefashionforbothrealms.Withregardtooutbreaksofviraldiseasesamonginsects,Vagohashighlightedtheexistenceoftwofactorsthatcanunleashmetabolicdisorders,andthatlieattheveryrootofdisease:theseare,justaswithplants,malnutrition and toxic effects.

9 Introduction

‘Agricultural Techniques and the Health of Crops.’

Basedonthetheoryoftrophobiosis,theeighthandninthchaptersdiscusstheresultsobtainedthroughtheprocessofstimulatingproteinsynthesis.

Here we review various examples of agricultural techniques, especiallythatofbalanced fertilisation(aphraseusedfrequentlybutquiteimprecisely).Suchabalanceimpliesthe prevention and correction of deficiencies.Ofcourse,suchtherapyoughttobebasedonstilldeeperknowledgeofthephysiologyofplants,especiallytheroleofvariouselements,chiefamongthemthetraceelements.Someextremelyencouragingresultshavealreadybeenrecorded.Sincesomeofthesefindingsstemfromanempiricaluseoftheprinciplesoftropho-biosis,wefeeljustifiedinhopingthatthistherapywillproveallthemoreeffectiveonceitisappliedwithfullknowledgeofthefactorsbehindit.

Balizac,July20,1984.

10 Healthy Crops

11 Resurgence of Diseases and Pest Damage Brought about by Pesticides

PART ONE

Pesticides and Biological Imbalances

Currentconcernsaboutsavingtheenvironmentleadustoreducepesticideapplicationsasmuchaspossible.Itwouldbeparadoxicalifweshouldatthesametimeextendtheuseofthesesubstancestoareaswheretheyhaveneverbeenusedbefore.Weruntheriskofpayingahighpricesometimeinthefuture,foratemporaryimprovementofyieldsinafewspecialareas.

ÉmileBiliotti1

12 Healthy Crops


Chapter I

Resurgence of Disease and Pest Damage Brought about by Pesticides

I. Serious concerns about crop health

Thearrivalofartificialpesticidesbroughtnewproblemsforcropprotec-tion.Mites,forinstance,onlyadvancedtotherankofa‘major’threattoagri-cultureafter1945,asnotedbytheeminentacarologist,Mme.Athias-Henriot(1959).Thesameistrueoftheleafsuckers(Psylla)2nematodes,aphids,andevenlepidopteraandcoleoptera,and‘numerousoutbreaksofdisease,’thatcannotbeaccountedforintheusualway.

One pesticide company expressed its amazement about the constantspreadofdiseasesaffectingcereals,andtheappearanceofnewviralinfec-tions,callingthem‘diseasesofprogress’.Thissamecompanyadds,‘Ifcertaindiseases have, so rapidly, become so serious, theremust be other factorsinvolved beyond natural and climatic conditions.’ (Publicity statement byMaisonProcida.)

Wewholeheartedlyendorsethisremark.Eventhoughitdisappearedfromsubsequent advertising, it sumsup the situationperfectly.We shall comebacktoitlater,inthechapteroncerealcrops.Withregardtoviraldiseasesinvegetablecrops,itisworthcitingthesomewhatdisillusionedobservationsofaspecialist:

‘Since vegetable growers have become familiar with their crops’ mainparasitesandhaveobtainedeffectivefungicides,viraldiseaseshavetakenonfargreaterimportance.Thesediseasesarefearedbecausetheiroriginseemsmysteriousandtheirdevelopmentinsidious’(Marrou,1969).

Fig. 1. Coefficients of the attack by grape Oïdium on grapes, according to the use of different antifungal chemicals employed against mildew. (Cabvernet-Sauvignon vine. Trials at Latresne, 1966.) Results of Chaboussou.

Coefficient of attack, per 400 grapes.

GRAPEVINE: trial blocks / Latresne / repercussions on Oïdium.

folp

et (P

halta

n)

Bord

eaux

mix

ture

2

Bord

eaux

mix

ture

0.5

capt

an

zine

b

prop

ineb

man

eb

700

500

300

100

cont

rol

2632.5

42

124

335

657

744 745


Wewouldliketonoteattheoutsetthatthe‘effective’fungicidestowhichherefersarethenewsyntheticorganicchemicals.Notonlyshouldwehavereservationsabouttheireffectiveness;theyalsobringwiththem,asweshalllatersee,gravedisadvantages.

II. Chemical pesticides are directly implicted in ‘biological imbalances’

Theauthoritieshavebeenforcedtotakeintoaccount‘thesideeffectsofanti-parasiteproductsforagriculturaluse’.InFrance,acommitteecomprisedofrepresentativesofINRA(NationalAgriculturalResearchInstitute)andtheCropProtectionDepartmentregularlydrawsupalistofaspecificpesticide’s‘disadvantages’inrelationtoonecategoryofparasiteoranother.Forthemostpart,thepesticidesinvolvedarechemical.

Thevocabularyusedtodescribetheserepercussionsdependsonwhetherthey arepest infestationsordiseases. In the repertoireof ‘side effects,’ theterm ‘proliferation’ is usedwhen the subject is the spreadofpests (mites,aphids,coccus,3etc.).Incontrast,whendealingwiththespreadofdisease(Oïdium, mildew,Botrytis, scab, etc.),4 it is assumed that the pathogenicagentisshowing‘resistance’tothepesticideinquestion.

Theuseofsuchdifferenttermstodesignatethesebiologicalimbalances,whetherintheanimalorplantkingdoms,arisesfromtheexplanationthatisofferedforthesephenomena.

Theclassicalexplanationforoutbreaksofpestsasaresultofonepesticideor another is that the pesticide has destroyed the natural predators.Withthe suppression of the restraints exercised by phytophagous predators orparasites,proliferationseemstogrowmoreserious.

This explanation disregards our own studies ofmite outbreaks due todifferent pesticides (Chaboussou 1969, and other publications). It alsorejectsstudiesthatshowhowaphidinfestationsmayactuallybecausedbydifferentpesticideproducts(Michel,1966;Smirnova,1965,etc.).Weshalltakeupthissubjectagaininaspecialchapter.

This is not to deny the noxious influence of pesticides on natural predators. But the different studies show quite clearly that these pest proliferations are chiefly the result of an increase in the biotic potential of the pests feeding on treated foliage. This includes, among mite populations and the like,anincreaseinfecundity,longevity,fertility,andratiooffemalestomales.

16 Healthy Crops

Many pesticides greatly increase the numbers of mites, despite beingharmlesstotheirnaturalpredators.Whatismore,thechlorine-basedprod-uctsusedto‘disinfect’soilactuallyincreasethenumberofmitesonpotatocropsgrownonthissoil.

Theresurgenceofoldmaladiesorthedevelopmentofnewonescannotbeexplainedbythedestructionofantagonistsbythepesticides,sincesuchantagonistsareveryrare.Peoplespeakof‘resistance’tothespecificpesticide,butwithoutgenuinelydemonstratingthis.Inreality,itisapparentlymoreaquestionof a ‘proliferation,’nutritional inorigin, causedby theparticularfungicideanditsharmfuleffectontheplant.

Fungicides, herbicides and pesticides, as we shall see in the followingchapter,haveaneffectonthephysiologyoftheplant,aboveallwhentheyareusedrepeatedly.

Theremayalsobeaselectionofresistantorpre-resistantstrains.

Wehave shown inexperiments that, ascompared tograpevines treatedsolely with pure water, treatments using various dithiocarbonates (zineb,maneb,propineb)broughtaboutasignificantincreaseinattacksofOïdium.VanevandCelebiev(1974)havealsoshownstimulationofthedevelopmentofOïdium(Uncinulanecator)5andgreymould(Botrytiscinerea)ongrape-vinesbyzineb-basedchemicals(Fig.1).

Itseemslogicalthatthese‘biologicalimbalances’broughtaboutbychem-icalpesticides,whether in theanimalorplantkingdoms, shouldhave thesamecause.Thus captan, thoughharmless tonaturalpredators,producesnotonlyaproliferationofmites,butalsoofOïdiumontheapple tree. Inaddition,itpromotesdevelopmentofthebacterialdiseasecrowngallonthecherrytree(DeepandYoung,1965).Theseauthorsstatethattheirfindingsdonotcoincidewiththetheoryofantagonism.Theysuggestthatotherfactorsmustberesponsible for thegrowthof the tumour.Hereagain,everythingpointstothefactthatitisthenewphysiologicalstateoftheplant,createdbythepesticide,whichhaspromotedthedevelopmentofbothcrowngallandOïdium. In a subsequent chapter onbacterial disease,we shall studytherelationbetweenplantsandtheirbacterialparasitesandshowhowtheplantshavebeenaffectedbyvariousenvironmentalfactors,suchaspesticidetreatments.


Notes1 FormerchiefinspectoroftheNationalInstituteofResearchinAgronomy(INRA),on

thesubjectofprotectingplanthealthincerealcropproduction-Phytoma,No.272,March1975,pp.21-23.]

2 E.g.Psillamali(appleleafsucker=psylladupommier),Psyllapirisuga(pearsuckerorpearpsylla=psylladupoirier),orTriozaviridula(carrrotpsyllid=psylledelacarotte).

3 Coccus:;‘aspheroidbacterialcell’(Microbiology)[fromAcademicPressDictionaryofScienceandTechnology]

4 Tavelure=(1)scab(Fusicladiumpirinum-pearscab,orFusicladiumdentriticum-applescab,or(2)leafspotofcurrent:Pseudopezizaribs).

5 Oïdium(French)=(e)Oidium=(e)powderymildew=(dt)Faulschimmel. Powderymildewisofthreetypes:Sphaerothecamacularspp.Oidiumspp.(Quercus)

=Microsphaeraspp.

III. Conclusions

Thegoalofthisbookistoexplainthereasonsforthefailureofchemicalpesticides,whetherfungicides,insecticidesor(aboveall)herbicides.Therootcauseistheirimpactonthephysiologyoftheplant,aphenomenonthatuptonowhasbeenoverlookedbyclassicalplantscience.Thefollowingchapterwillbespecificallydevotedtoplant-parasiterelationships,highlightingthegreatimportanceofenvironmentalfactorsfortheplant’ssusceptibilitytoitsvariousparasites.Weshalltrytoshowtheconvergenceoftheeffectsofthesefactors,biochemicalinnature,ontheplant’ssusceptibilityorresistance.Theageofthevitalparts,thedevelopmentalstage,theclimate(temperatureandphotoperiod),thesoil,andthevarietyallplaytheirpart.Wewillanalysethenatureoftherelationsbetweentheplantanditsparasites,relationsthatareprimarilynutritional.

Wewill look at the nature of those nutritional elements that favour the biological potential of parasites, and thus identify the physiological state of the plant that will maximise resistance.

Chapter 2

Plant-Parasite Relations: the Trophobiosis Theory

I. The influence of environmental factors on the resistance of plants

A plant’s physiology and resistance are determined by environmentalfactors.Wewillreviewacertainnumberofthesefactorsinordertoestablishthenatureoftherelationshipbetweentheplantanditsparasites.

1. The influence of the physiological stage: the period of flowering.

Canthetheoryoftrophobiosisexplainhowfloralinductioncouldchangethebehaviourofaplant?Floral inductioncanchangeaplant’sbehaviour,especiallyitssusceptibilitytodisease,aswehavealreadyarguedelsewhere:

‘Onefactseemsclearlytoconfirmthisview:thestageatwhichinfectionsoccur.Accordingto theauthors, thisperiodofheightenedsusceptibilitycorresponds to themomentofflowering. It is in fact at themomentofflowerformationthatalltheleaveslosetheircapacityforphotosynthesis.They even undergo a certain amount of decomposition of their ownproteins.Thisallowsthemtosupplythereproductiveorganswithsolublesubstances.

‘Thismeansthatinthefloweringstate,andstillmoreduringthedevelop-mentoftheyoungfruit,theplantisaffectedbyacuteproteinbreakdown(proteolysis),withaverycleardropintheproteincontentofthematureleaves.’1

19 Plant-Parasite Relations: the Trophobiosis Theory

Wealsoadded:

‘This flowering period therefore constitutes a primary period of vulnerability for perennial plants (as well as annual ones.’

Wewillnowexaminetheinfluenceoftheageofthepartsoftheplant,aswellasoftheclimate-eachofwhichhasanimpactontheother-onthesusceptibility of theplant todiseases, taking as our example the relationsbetweenthegrapevineandmildew.

2. The Influence of the Age of Plant Parts on Susceptibility to Disease.

Wewilltakeseveralexamples,highlightingatthesametimeseveralplantsandvariousparasites.

a) The grapevine and mildew

TherelationbetweenthegrapevineandmildewhasbeenparticularlywellstudiedbyPantanelli(1921).Wecansumupthesestudies inthisway:anattackofmildewpresupposes

• germinationofthespore(conidium);• attractionofthezoosporesbythestomata,toallowthemtopenetrate.

Pantanelliobservesthat,whilethehumidityofthesoilhasamajorinflu-enceontheopeningofthestomata,condensationofwaterontheleaveshastheoppositeeffect.So,idealconditionsforamildewattackarecreatedbyahumidnightfollowingahotdryperiod.

However,humidityconstitutesasecondimportantconditionfortheattackbecause it influences thenutritive exchanges in the leaf tissues.Pantanelliascertained this by comparing the compositionof leaves fromvineplantsgrowninpots.Whilesomewereplacedoutdoors,otherswereputinsideahumidandwell-litroom.Inthelatter,theproportionofsolublecarbohydrateswashigherthanthatofstarch(whichhadalmosttotallydissolvedduringthenight).Thus,theproportionofnitrogenandphosphorouscompoundswasalsoraised,whichencouragedgermination.

Asfortemperature,italsohasanimportanteffect,notonlydirectlyonthefungus,butalsoindirectlyonthemetabolismoftheleaf.

20 Healthy Crops

Weknow that spores germinate better if they have first been cooled to9-10oC.Thiscool-ingalsohasaneffectontheleaf:itproducesanincreaseintheproportionofsugars, incomparisontothestarchnotyetdissolved.Moreover,thereisaslightincreaseinthepro-portionofsolublenitrogenandphosphorous.

Thiswholeprocessexplainswhyinfectionsaremorelikelytotakeplaceatdawn.Thisisthemomentthatcombinesthegreatestbreakdownofstarchwithmaximumdecompositionofproteins.

Boththeinfluenceofhumidityandthatoftemperaturecombinetohigh-light thegreat importanceof soluble compounds formildew infectionsofgrapevineleaves.Thecompoundsdothisthroughtheirnutritionaleffects.Theseeffectsareconfirmedbyanalysisoftheinfluenceoftheageoftheleaf.

‘The very young leaves,’ as Pantanelli notes, ‘do not become infected,becausetheycontainamuchhigherquantityofalbumin,togetherwithanalmosttotalabsenceofsolublecompoundsinthewater.Olderleavesbecomeinfected,butinadultleavesthedevelopmentofthemyceliumisveryslow.’

As Pantanelli concludes, ‘Themost favourable conditions for amildewinfectionarecharacterisedbyahighproportionofsugarcomparedtostarch,andofsolublenitricandphosphoriccompoundscomparedtoinsolubleones(that is to say, in comparison to albumin,nucleinandproteins).The freeorganicacidsdonotseemtoplayarole.’

Inageneralway,thisalsoexplainstheresistanceofthematureleavestoinfections:theyhavealowleveloffreenitrogencompounds,sincethebulkofthenitrogeniscontainedintheprotein(MacKeeH.S.,1958).

Pantanelli (op.cit.)alsostudied thebehaviourof thezoosporesmakingtheirwaytowardsthestomata.Hewasabletoestablishthat

• neither the glucose nor the saccharose attract the zoospores, whilepeptoneattractsthemstrongly.

• thefreeacids(tartaric,malic,citric,oxalic)repelthem.• alkalinesalts(includingsodiumcarbonateandpotassiumcarbonate)

andmetallicphosphatesrepelzoosphores.

Finally,Pantanelliconcludedthathisfindings:‘aresufficientlyinlinewithwhathasalreadybeenestablishedaboutaleaf’scompositionattheinstantofattack: solublenitrogenandphosphorouscompoundsappear tohaveagreaterpowerofattractionthanthesugars.’


Sincenosugarorothercarbohydrateisvolatile,itisverylikelythatwhatattracts the zoospores are the amino and ether compounds of fatty acids,particularlyaminoacidcompounds.

‘In fact,’ says Pantanelli, ‘both peptone and cheese extract have a char-acteristicodour,mainlydue tovolatileaminocompounds ...Sugar,whichstronglyattractsotherfungi,hasonlyminorimportanceforthezoosporesofthePeronosporae’.2

Pantanelli’sstudyofthegrapevine-mildewrelationshipclearlyshowstheimportanceofsolublenutritionalelementsincontaminationandinfectionby pathogenic fungus. This occurs in the context of ametabolismwhereproteinbreakdownpredominatesoverproteinsynthesis.Itimpliesagreaterexudationofsolublecompounds,namelynitrogenoussubstancesandsolublesugars,onthesurfaceoftheleaf.Althoughsugars,asPantanellihasdemon-strated,appeartoplayonlyasecondaryroleinthecaseofPeronospora,thismaynotbethecaseforotherfungi,whichseemtorequirelargequantitiesofcarbohydrates.

It therefore appears that the impact of the nutritional ratio (solublenitrogenelementstoreducingsugars)onthecontaminationprocessvariesaccordingtothespecies.(Wecallthisratio,moresimply,theC/Nratio.).

TheC/Nbalance,asweshallseeconfirmedbelow,isdependentonvariousotherenvironmentalfactors,suchasclimatesoil,fertilisation,and–lastbutnotleast-theimpactofpesticides.Thesefactorswillbediscussedlateron.

Forthemoment,wewillstudytherelationbetweentheageoftheplant’spartsandtheparasite(whichinthiscaseisaviraldisease).

b) Tobacco and mosaic virus

Viraldiseasesarenoexceptiontotherulethattheageoftheleavesaffectstheir susceptibility. Horvath (1973) showed that the susceptibility of thetobaccoplanttomosaicvirusdependsonthepositionoftheleavesonthestalk - in otherwords, on their age.There is an increase in susceptibilityamongthefirstsenescentleavesatthebase.ThiscorrelateswiththerateofsynthesisofproteinsandRNAintheleaves,whichislowerthantherateinotherleaves.

22 Healthy Crops

If, therefore, a certaindegreeof senescencemakes themhypersensitive,thephenomenonissuppressedinhighlyjuvenileleaves.Hypersensitivityischaracterised,asthetermindicates,byextremesensitivityofthehostcellstowardtheparasite,whetherthisisapathogenicfungusoravirus.Atlength,thishypersensitivitycausesthecellstodie.Thishaltstheinfection,becauseoftheabsenceofnutritionalelements.Eveninthisspecialcase,therearestillnutritivefactorsplayingaroleintheprocessofplantresistancetoparasiteintrusion.

Susceptibilityoftheplant’spartsinrelationtotheirageisequallyimpor-tantwhenitcomestonoxiousinsects.Researchershaveproventhis,aboveall,inthecaseofsuckinginsectssuchasmitesandaphids,towhichweshallreturnlater.Forthemoment,wetaketheleaf-hoppers(Cicadellidae)asanexample.

c) The castor oil plant (Ricin) and the leafhopper. The mechanism of resistance of varieties

Withregardtomites,wehaveshown(alongwithotherauthors)thattheirproliferationislinkedtoadietrichinsolublesubstancessuchasfreeaminoacids,alongwithreducingsugars(Chaboussou,1969).Theprocessisanalo-gouswithaphids,whosenumbersatthistimecontinuetogrowasaresultoftheuseofcertainpesticides.

Aswithmitesandaphids,theleafhoppers(Cicadellidae)andpsyllidsarebothmajor threats to crops. Infestations are recordedongrapevines thathavebeentreatedwithorgano-pesticides(fungicidesaswellasinsecticides)(Chaboussou,1971).

In-depth studieshavebeen carriedout in Indiaby Jayaraj (1966, 1967)intothenatureof therelationsbetweenthecastoroilplant’sbiochemistryandtheattractionandreproductionoftheleafhopperEmpoascaflavescens.Hetouchedonafactorthatwehavenotconsidereduptonow,thatofdeter-minismaccordingtovarietalresistance.Thisshowstheinfluenceofgeneticfactors. Jayarajwasable toestablish thatvarietal resistance isexpressed intermsofnutritionalvalueinrelationtoinfestationsbyleafhoppers.Invari-etiesclassifiedassusceptibleormerely ‘tolerant’ to infestation,wefindanaccumulationoffreeaminoacidsandamines.


In contrast, the resistant variety containsmore sugars than the suscep-tible or tolerant ones, while the latter contain, respectively, 113.5% and42.3%morenitrogenthantheresistantvariety.Thesusceptibleandtolerantvarietiesshowed12and7timesmorefreeaminoacidsthantheirresistantcounterparts.

Jayaraj’sconclusionswereveryclear:‘TheresistantvarietiesofthecastoroilplanthaveatendencytorepulseE.flavescensduetotheirlownutritionallevel,asindicatedbytheirlowlevelsoftotalnitrogenandofaminoacidsandpeptides’.

Tosummarise,alackofnutritionalelementsisattherootofresistancetoinfestationsbytheleafhopper.Wefindsimilarpatternsofresistancetootherinsects,suchasaphids,aswellastopathogenicfungi(cryptogamicdiseases),bacteria,andviruses.Weshalllookatthelevelsofthesesolublecompoundsandtheirproportions,intermsoftheC/Nrelationship.

Thestudyoftherelationsbetweenanotherleafhopper,Empoascafabae,and thepotatoplant likewise shows theextremesensitivityof leafhopperswith regard to thebiochemicalnatureof thehostplant.MillerandHibbs(1963)wereabletoestablishthat,inthecaseofthepotatoplant,Empoascafabaepreferredunpairedterminalleafletsoversubterminal-pairedleaflets,theformerreceivingsignificantlymoreeggs.Suchaselectionofegg-layinglocationdependsuponthebiochemicalcharacteristicsoftheleaflet.

Thisexampleshowsthatnutritionalstatedeterminesresistance.Itisthefundamental element, throughout this whole study, in the phenomenonof resistance.Resistance is a functionof thevariety (genetic factors)oroftheageofthetissues.But,asweshallnowsee,resistancealsodependsonclimateandthenatureofthesoil.

Theseresultswillhelpustograspbetterthemechanismsbywhichpesti-cidesimpactonthephysiologyofthehostplant,promotinginfestationsofvariouspestsanddiseases.

3. The influence of climate

a) Temperature

ThisfactorhasalreadybeentoucheduponinPantanelli’sstudiesonthegrapevine andmildew. Although temperature has a direct influence on aspore’sgermination,itisequallydependentuponthenatureofaleaf’s

24 Healthy Crops

exudates, inotherwords their richness in solublenutritional compounds,especiallynitrogen.Thenatureandquantityoftheseexudatesarestronglydependentontemperature.

AsDufrenoy(1936)writes: ‘Foreachvarietyofwheatandeach typeofPuccinia glumorum,Gassner andStrait showed the existenceof a criticaltemperature,abovewhichthewheatisresistant.Ingeneral,lowertempera-turesetsoffanincreaseinquantityofsolublealbuminoidesinthefirstleavesofthewheatseedling.’

ThiswouldappeartoconfirmFischerandGausmann’sresultswithregardtotheparallelsbetween‘theincreaseinsolublealbuminoidaltissuesandtheincreaseinsusceptibilitytorust.’

GROWTH ON SHORT DAYS

Low K - High Ca

Higher level of soluble N

Lower level of protein N

Proteolysis accompanied by a greater accumulation of asparagine

Lower level of soluble N

Higher level of protein N

Proteogenesis in conditions of high levels of glutamine

Fig. 2. Diagram showing the combined influences of the relation between the cationic ele-ments K and Ca and the phenomena of protein synthesis and proteolysis, as well as the in-fluence of the photoperiod on the level of certain amino acids in the leaves of Mentha piperita. (After Crane and Stewart, 1962.)

GROWTH ON LONG DAYS

High K - Low Ca


This sensitisation of the wheat plant to disease through a reduction intemperature, in other words by a slowing down of protein synthesis, fitsperfectlywiththenutritionalbasisofourtheoryoftrophobiosis.

In passingwe should point out that the increased susceptibility to rustbroughtaboutbyachlorineproductsuchasDDTisthedirectconsequenceofthispesticide’seffectontheplant’sphysiology(Johnson,1946).ThiswouldappeartobeduetoasimilarnutritionalprocesstothatwhichliesattherootofDDT’sencouragementofaphidproliferation.Thisinvolvedinhibitionofthe process of protein synthesis and accumulation of soluble nitrogenoussubstancesinthetissues(Smirnova,1965).Weshallreturntothissubjectinexaminingintensivecerealproduction.

b) The influence of latitude and the photoperiod

Latitude and photoperiod have often been linked to crop resistance todisease.Youngetal. (1959)noticedan increase in themaizeplant’s sensi-tivity toDiplodia zea when a hybrid ofmaize from a northernUS state,suchasMinnesota,wasplantedinamoresouthernstate,suchasMissouriorOklahoma.Thisphenomenonarosefromthefactthatthelowerlatitudebringsaboutareductionindaylength.

This may well be a general phenomenon. Umaerus (1959) found thattheSebagopotato,fiercelyresistanttomildew(Phytophthorainfestans)inMaine,withitslongdaylighthours,wasoneofthevarietiesmostsusceptibleinFlorida,withitsmuchshorterdays.

Such facts can be explained ‘biochemically.’ Crane and Stewart (1962)showedthat,inthecaseofMenthapiperita,thetissuecompositionofaminoacidsvariedasafunctionofthephotoperiod,butalsoaccordingtotheK/CAbalanceinthenutritivesolution(fig.2).

CraneandStewart’sresults(op.cit.)canbesummarisedthus:

i)Shortdaysaccentuatetheretentionofsolublecompoundsinthetissues.Proteinbreakdownincreaseswiththeshorteningofthephotoperiodandisaccompaniedbyanaccumulationofasparagine,anaminoacidthatweshalloftenencounterasafundamentalnutritionalfactorforthedevelopmentofpathogenicfungi.

ii)duringlongdaystheamountofsolublenitrogenislowerbutquantitiesofproteinnitrogenarehigher.Theplantisinaconditioninwhichproteinsynthesisdominates,characterizedbyhighlevelsofglutamine.

26 Healthy Crops

CraneandStewart’sresultsfullyconfirmtheinfluenceofthephysiologicalstateoftheplantonitssusceptibilitytoparasites,andalsoleadustoconsidertheinfluenceoftheplant’snutritiononthebiochemicalcompositionofthetissues.Herewetouchontheinfluenceoffertilisationonacrop’sphysiologyandthusonitssusceptibilitytoparasites.

CraneandStewart(op.cit.),instudyingtheeffectsoftheK/Cabalanceonthenutritivesolutioninrelationtotissuecomposition,showthattheseeffectsare additional to those attributable to the photoperiod. This particularlyappliestotheequilibriumbetweenproteinsynthesisandproteinbreakdown(fig.2).

Sucheffectsontheresistanceofplantsexplainthoseofasimilarnaturebroughtaboutbysupplementsandfertilisers,asweshallseelater.However,fertilisersalsohaveimportantrepercussionsforthenutritionalvalueofthecrop,andconsequentlyforthehealththosethatfeeduponit:peopleorlive-stock.Thisaspectofthequestionleadsusdirectlytoinvestigatetheinfluenceofthesoilitselfontheplant’sresistance.

4. The influence of the nature of the soil

a) The Colorado beetle and the potato plant

Togetherwith the fruit fly and the silk worm, theColorado beetle hasrenderedgreat services to science, thanks to the studies carriedouton it.Ithasmuchtoteachusabouttheinfluenceofthenatureofthesoilonthepotatoplant’ssusceptibilitytothiscelebratedColeopter.

Chauvin(1952)wasabletomeasurethefeedingactivityoftheColoradobeetleondifferentvarietiesofpotato,inrelationtosoilconditions.Twotestsiteswereestablished,oneanexposedsiteinVersailles(siteA),theotheronclayeysoil,nearEpernon(siteB).(Nofurtherdetailsofthesoiltypeweregiven).

These tests showedmajor differences in the ‘appetite’ of the Coloradobeetle,fromwhichChauvinattemptedtodeducetheecologyoftheattractingsubstances.Foreachvarietyofpotato,hewasabletoassignwhathecalledits‘attractionunits’forthebeetle.

Foreachvariety,theresultsshowedingeneralthatthepotatoesonsiteBsufferedfewerattacksthanthosecultivatedatsiteA(Table1).


Table 1: Units of attractiveness for the Colorado beetle, shown by several varieties of potato, in relation to the situation.

Situation Bintje Saucisse Ackersefen Parnassia

A 1.25 0.45 1.61 0.80

B 0.31 0.28 1.25 0.28

These studies on the Colorado beetle, including for instance those ofBoskozska(1945),clearlydemonstratethatthetypeofsoilandthusofthefertilisertreatment,hasaneffectonthepotatoplant’sphysiologyandthusits susceptibility to infestationby theColoradobeetle. It should thereforecomeasnosurprise thatcertain traditionalgrowingmethods,suchas thesystematicapplicationofmanureandcompost,encourageresistancetotheColoradobeetleandeventodisease,throughthebiochemicalstatethattheycreateintheplant.Wewillreturntothissubjectwhenweexaminetheeffectsofbothfertilisationandtheplants’needsontheirresistancetoparasites.

b) The disease ‘resistance’ of certain soils

Therehasbeenresearchintowhathasbeentermed‘asoil’sresistancetodisease,’ofasimilartypetothatdiscussedinrelationtothepotatoplantandtheColoradobeetle.

Aspecialiston thesubject,Louvet(1982), remarkedthat thisresistancecouldbelinkedtothechemico-physicalcompositionofthesoil.SoilswithahighpH,forinstance,areresistanttoclubroot,3afungaldiseaseaffectingcabbages.Inothercases,thebasisofthisresistanceisfundamentallymicro-biological. According to Louvet, immunity is related to ‘efficientmicrobi-ologicalbarriers’whichprevent thepathogenic agent frompromoting thedisease,evenwhenitispresentinthesoil.

AsLouvetstates,‘Thisincompatibilitybetweenthepathogenicagentandthe soil-plant interaction is the result of an activeopposition;when thesemicrobiological barriers are broken down, the resistance is destroyed. IntheDurancevalleyofFrance,melonsgrowninsoilsfumigatedorheatedtoeradicatecorky-rootendupdevelopingstalkrot.4

28 Healthy Crops

In thisexample, interferencehasbroughtabouta ‘biological imbalance’similar to those provoked by synthetic pesticides, though in this case theprocessesaremorecomplex.If,asislikely,thesetreatmentsofthesoilleadtothedestructionofthesoil’smicroorganisms,thenthecentralissueistheplant’snutritionalprocess,andthusitsresistancetodisease.

Thisallleadstotheconclusionthat‘theincompatibilitybetweenthepath-ogenicagentandtheplantsoilsystem,’ofwhichLouvetwrites,isactuallyduetothephysiologicalstateoftheplant.Wearealreadyawareoftheimportanceofspecificmicroorganismstoaplant’snutritionalprocess,mainlythroughtheir impactsonnitrationandnitrification,processeshaltedby fumigantswhichdestroythemicroorganisms.

Otherexampleshelp todemonstrate thecomplexrelations that link thesoil, a plant’s physiology, and its resistance to various parasites. Throughbothfieldand laboratory research,BrainandWhittington(1981)demon-stratedthathighlevelsofmanganeseintissuesoftheswedeplantloweredthesensitivityoftheplant’sleavestoOïdium.Thisconfirmspreviousresearchthatmanganeseisavitaltraceelement,essentialforaplant’sgrowth.

Anydeficiency,especiallyintraceelements,leadstoaninhibitionofproteinsynthesiswithacorrespondingincreaseinfreeaminoacids.Itisknownthatmanganese is crucial for the absorptionof nitrates;manganesedeficiencysensitisestheoatplanttobacterialinfectionsbyinhibitingproteinsynthesis.

Everything would appear to confirm that ‘soil resistance’ is simply aspecial aspectof aplant’s resistance.Abalanceof various elements in thesoilcontributestoabeneficiallevelofproteinsynthesis.Thisdependsonthebalanceofcationicelements,mostnotablyKandCa,aswehaveseenabove;italsorequirestheinterventionofwhathavebeencalledcatalysingortraceelements,whichweshallreturntolater.

However,thepresenceinthesoilofoneoranothertraceelementisnotsufficient:theplantmustalsobeabletoabsorbthiselement.ThisiswherepHcomesin.BrainandWhittington(op.cit.)haveshownthatthehigherthepH,thefiercertheattacksofOïdium.Sincetheseattacksareassociatedwithareductioninmanganeseintheplanttissues,itistheabsorptionofthistraceelementthatisaffectedbythepH.ThepHhasaneffectontheactivityofthebacteriathatassistmanganeseabsorption:adeficiencyofmanganeseinlimestonesoilresultsfromthepHbeingtoohightoallowanyactivitybythiscategoryofbacteria.


AshighlightedbyBrainandWhittington(op.cit.),theeffectsofsoilpHareextremelycomplex.Changescanoccur,eitherbyincreasingtheavaila-bilityofcertainelements,leadingtotoxicresults,orbyareductioninuptake,leadingtovariousdeficiencies.

Theseindirecteffectswhichlinkplantphysiologywithresistance,throughthenutritionalroleofthelivingsoil,clearlydemonstratetherisksposedbythemyriadherbicides, insecticides, fungicides, andnematicides -particu-larlyartificialones,asusedonahugescale in ‘chemical’agriculture-andtheireffectson thesoil’smicroorganisms.Theseariseaboveall fromtheirimpactinprovokingdeficiencies.Weshallreturntothispoint,whichaffectsnotjustcerealsbutallcrops.

Asweshallsee,thetraceelementsplayafundamentalroleinplantresist-ance.Thisisdemonstratedbytherepercussionsofanydeficiencies,andthepreventionorcureofdiseasethroughthecorrectionofthesedeficiencies.

Therichnessofcertainsoilsintraceelementsmightexplainwhytheplantsthat grow there are resistant to disease. This is particularly the casewith‘volcanicsoils’.

c) The disease resistance of rice grown on volcanic soils

Martin-Prevel(1977)notedthatriceismoreresistanttoPiriculariaoryzwhengrowingonvolcanicsoil.Whenweconsidertheroleofspecifictraceelements in soil, such as copper and manganese, we can reasonably askwhetherthiskindofresistanceisduetothepresenceandavailabilityofthesetraceelementsissuingfromdeepintheearth.

To sumup, analysis of the effects of environmental factors on aplant’sdiseaseresistance-floweringperiod,ageoftheplantparts,climate,compo-sition of the soil, aswell as plant variety (genetic factors) - clearly showstheirimpactonthemetabolismoftheplant.Thisparticularlyappliestothetissuelevelsofsolublenutritionalelementssuchasaminoacidsandreducingsugars,uponwhichparasitesaredependenttodifferentdegrees.

Disease resistance inplant feeding insectsprovides furtherproofof theimportant role of plant metabolism and the ratio of protein synthesis toproteinbreakdown.

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d) Resistance to viral diseases, in relation to the nature of the soil used to grow the deedling, in the case of certain lepidoptera.

Vago (1956) showed that it appeared possible to trigger a pronouncedviralinfectionnotonlywheretherewasnopreviousinfection,butalsowhenactivelyguardingagainsttheentryofthevirus.Heshowedthataninfectioncouldbeprovokednotjustbyasub-lethaldose(forexample,bytheuseofsodiumfluoride)butsimplybycausingmalnutritionintheinsect.

In thecaseofVanessaurtica (cabbagewhite), feeding thecaterpillaronbrambleleavesleadstoconsiderabledifferencesintheproportionsofNuclearPolyhedrosisVirus(NPV),dependingonthetypeofsoilonwhichtheplantisgrowing(seeTable2).

Table 2: Proportion of NPV within Vanessa urticae, according to type of feed. Feeding on bramble leaves growing on clayey soil: 18%Feeding on bramble leaves growing on silty soil: 4%

Thisshowsclearlythegreat importanceof thenatureof thesoilanditsfertilisationforthenutritionalvalueoftheplant,notjusttodomesticanimalsbutalsotoman.Wewillreturntothissubjectlater.

Thequalityofaharvestresidesinitsnutritionalvalue,whichisnotalwayseasytomeasure.Ifitcaninitiallybemeasuredintermsofitsproteincontent(whichis,aswehaveseen,acriterionofitsdiseaseresistance),thiswouldexplainwhy research into the stimulationofprotein synthesis is thebasisofamorerationalapproachtoagricultureThehealthoftheplantandtheanimalsthatfeeduponitaredirectlylinked.

II. The relationships between plant and parasites

1. The Relations between Plant and Parasite Are Nutritional in Nature

Thevariousenvironmentalfactorsthatwehavelookedat-floweringstage,ageoftheleaves,thepartoftheplant,theclimate(temperatureandphoto-period),thenatureofthesoilandthegeneticfactorsthatgowithvarietallydeterminedresistance-havegivenusconvergingresultswithregardtotherelationshipsbetweenplant andparasite.Whether the issue is attackby apathogenicfungus,aninsect,amite,oravirus,therelationtothehostplantisanutritionalone.


The chapter on bacteria will show that the same is true of attacks bybacteria.Thisisaclearconfirmationofthevalidityofourtheoryoftropho-biosis,accordingtowhich:

‘Allvitalprocesses dependonthesatisfactionof theneedsof the livingorganism,whetheranimalorvegetable’(Chaboussou,1967).

In other words, thismeans that a plant will only be attackedwhen itsbiochemicalstatecorrespondstothenutritional(trophic)needsofthepara-siteinquestion.

Thetheoryalsopositsthatthesensitisingnutritionalfactorsarefoundinthesolublecompoundsof intermediatemetabolism:solublenitrogen(freeaminoacids)andreducingsugars.Thisdoesnotmeanthatallparasiteshaveidentical nutritional needs, but that they all draw from the same pool ofsolublesubstancesdissolvedintheliquidofthecellularvacuole.Wheretheprocessofproteinsynthesisdominatesoverproteinbreakdowninaplant,diseaseresistanceisstrongest.

Thusitseemsthattheratioofnitrogenouscompoundstoreducingsugarscould serve equally well as a criterion for determining susceptibility todiseases suchasnoxiouspests, dependingon thenutritionalneedsof thepest. The following chapters will show that soluble nitrogen compoundsarethemainnutritionalfactorspromotingthedevelopmentofthevariousinfections.

2. The presence of phytoalexines in tissues does not explain a plant’s disease resistance

The classic theory of trophobiosis holds that resistance is linked to thepresence in the plant tissue of ‘phytoalexines,’ substances that are antag-onistic toparasites.So far,however, there isnoproofatallof this theory.Numerousplantpathologistshaveexpresseddoubts,particularlyconcerningthesupposedfungotoxicityofphenolsandsimilarsubstancestopathogenicfungi.(Phenoliccompoundsandothertanninsaretheonesmostfrequentlycitedasbeingphytoalexines).

Tomiyama (1963) found that, although phenolic compounds may befungotoxic,thelevelisnotveryhigh.Asaresult,wecannotanswertheques-tionwhetherperoxydaseorphenolic compoundsplay any role in varietaldifferencesindiseaseresistance.

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Inthecaseofthepotato,ithasbeenshownthattheintracellularhyphaofPhytophthorainfestans(mildew)stayaliveevenaftertheepidermalcellsofthepotatohavedied.Infact,thehyphataketenhoursormoretodieafterthecell’s‘hypersensitive’death.Thefungus,therefore,seemstodiethroughlackofnourishmentratherthanthroughtoxiceffects.Itmightbethesameforcertainclassicfungicides,suchasBordeauxMixture(whichhascertainsideeffectsthatcannotbeotherwiseexplained).

Ontheotherhand,Tomiyamanotes,‘Thebuild-upofstarchandincreaseinprotein,phenoliccompounds,andrespirationindicatethatthecompoundscirculatingthroughtheplantarelinkedtoanacceleratedmetabolismintheplanttissue,whichbecomesresistanttoparasiteinvasion.’Ifwehaveunder-stood correctly, this corresponds to ametabolismwhereprotein synthesispredominates, leading to a minimum of soluble nutritional substances,whichexplainstheresistance.

Cruikshank(1936)expressessimilardoubts:‘Testinginvitrothetoxicityofsometoxinorothercannotyieldacompleteexplanationofitsroleinvivobecauseitdoesnottakeintoaccountthedynamicnatureoftheparasite-hostinteraction.’Ashecomments,however:‘Onecannotdirectlyconcludefrominvivoobservationsofthecessationofgrowth,thatthephytoalexinesarethecause,orthat,eveniftheydonotintervenehere,theyplayaprimaryroleindiseaseresistance.’

Such experiments cannot therefore confirm any toxicity of the variousphytoalexinestopathogenicfungi.

As Kiraly (1972) points out, ‘Hypersensitive necrosis in relation to theproductionofphytoalexineisonlyaconsequence,notthecause,ofresistanceinpotatoes,beans,andwheattothedifferentfungi(Phytophthorainfestans)andtorusts.’

Kiraly adds: ‘In other words, in the natural host-pathogen interaction,characterisedbyanincompatibility,itwasnotthenecrosisofthehosttissueswhichinhibitedorpreventedthedevelopmentof thepathogen.Instead, itwasoneormoreunknownmechanismswhichinhibitorevenkillthepath-ogenbeforethestartofthenecrosis.’

The‘relationbetweenthehostandthepathogen’isthecruxoftheproblemwhenlookingforevidenceoftoxicsubstances,asDunez(1983)remindsus..


Similarly, Obi (1975) found that numerous types of the maize plant’sresistancetoHelminthosporium turcicumarenotdueto theproductionofphytoalexines.

According toWood(1972) (perhapsoneof theresearchers tohavebestanalysedthemechanismofaplant’sresistancetodisease),‘Ahost’sresistancecandependupontheabsenceornon-availabilityofthesubstancesnecessaryfortheparasite’scontinuedgrowth,oruponunfavourableconcentrationsorproportionsofessentialnutritionalsubstances’.

Wood(op.cit.)hasalsocomeupagainstthedifficultiesofexplainingresist-ancethroughthepresenceofphytoalexines.Inhisview,weknowpreciouslittleabouttheprocessesofdisease-resistance.Hepointsout,however,thatasthetissuesgetolder,thespecificresponsesarereplacedbyamoregeneralresistance,herecalled‘adultplantresistance’.

McKee(1956)notedthatthematureleavesofthetobaccoplantarechar-acterisedbyanexcessofproteinsynthesisoverproteolysis.Similarlyinthecase ofBryophyllum, the ratioNproteins:N amino acids is 17.4 in veryyoung leaves, 15.9 in young leaves, and 28.8 in adult leaves (Champigny,1960). Theseexamplesconfirmthatahigh levelofproteinnitrogenandcorrespondingly low levels of free amino acids can, in a generalmanner,explainthe‘nutritional’resistanceofadultleavestotheirvariousparasites.

‘Theproductionofphytoalexines,’ Smith (1980) recognised, ‘constitutesonlyoneofthecomponentsofthecomplexactivemechanismthattheplanthasatitsdisposal.’Oftheelementsthatpotentiallyplayarole,hecites(apartfromthe ‘thereleaseofpreviously formedantimicrobialcompounds’) ‘themodificationofthestructureofthecellwalls’and,finally,‘interferencewiththefungi’snutrition’.

InastudyoftherelationbetweenBotrytiscinereaandtheharicotbean(Phaseolus vulgaris), Garcia et al. (1980) concluded that ‘there was nocorrelationbetweenvirulenceandsensitivity tophytoalexines,orbetweenvirulenceandcapacity tobreak themdown, the iso-latesbeingcapableofmetabolisingthefourphytoalexines’.

Certainresearchersinthisdebate,however,citetherelationbetweenresist-anceandprocessesthatpromotethesynthesisofproteins.ThusAlbersheimetal.(1980)highlighttheroleofaspecifichormonewhich‘wouldappeartoprotecttheplantbyinducingthesynthesisofproteinswhichactbyinhibitingthedigestiveenzymesofinsectsandbacteria.’

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Nothingconvincingispresentedtosupportthishypothesis,however,sowemuststillaskifstimulatingtheprocessofproteinsynthesis hasapositiveeffectonresistanceasasimplecorollaryofthedecreaseinsolublesubstances,principallyheldtobeatthebasisofthe‘nutritional’sensitivityoftheplant.

Fritig,whohadthetaskofdrawingconclusionsfromthisdiscussion,andwhotookintoaccountthefactthatthevariousauthorsdidnotattributeamajorroletothephytoalexinesintheprocessesleadingtoresistance,drewattention to the fact that according to different authors ‘the build up ofphytoalexineswasprecededby a generalmetabolic stimulus, implying anincreased synthesis of mRNAs and then of proteins.’ In other words, heconfirmedourunderstandingoftheresistanceprocesses.

Tosumup,thestudiesthatwehaveanalysedwouldappeartoconfirmthatfungotoxicityisnottheroleplayedbyphenolsandothertannins,asalludedtobyCruikshand(op.cit.)andpromotedbyDufrenoy.Wearenowgoingto see how this physiologist’s concepts allow the various, and seeminglycontradictory,hypothesestobeintegratedwithrespecttothedeterminationofresistance.

3. Nutritional elements are in balance with phytoalexines

Allofthedifficultiesinestablishingvalidcorrelationsbetweentheplant’sresistance and the presence of certain phytoalexines in the tissues areexplainedby the fact that thephytoalexines areoften inbalancewith thenutritionalelementstowhichresistanceisattributed.

HerewemustrecallDufrenoy’sobservations,thatimmunitytodiseaseislinkedto‘theconcomitanceoftwoantagonisticbiochemicalchanges:

• on theonehand, theproductionandbuildupof sugarsandaminoacidsinthevacuolarsolution,

• ontheothertheproductionofphenoliccompounds.’

Dufrenoy notes that ‘the abundance of phenolic compounds and thepaucity of amino acids appears to inhibit the growth or proliferation ofpathogenicmicroorganisms.Incontrast,anabundanceofsolublesugarsandaminoacidsguaranteesgrowthandproliferation.’


Dufrenoy(1936)addsthat‘circumstanceswhichareunfavourabletotheformationofnewquantitiesof cytoplasm- inotherwords, circumstancesunfavourabletogrowthingeneral-tendtoencourageanaccumulationofunusedsolublecompounds(sugarsandaminoacids)inthecells’vacuolarsolution.Thisaccumulationofsolublecompoundswouldappeartofavourthenutritionofparasiticmicroorganismsandthusreducetheplant’sresist-ancetoparasiticdiseases.’

AsDufrenoyexplicitlystatedelsewhere:‘Recentphysiologicalstudiestendto confirm the results of the cytological study: that a plant’s vulnerabilitytoitsparasitesisafunctionoftheabundanceofaminoacidsandsugarsinits vacuolar solutions.These aminoacids and sugars are eitherpresent intheplantbecauseofanutritionalimbalanceoraretheresultoftheproteinbreakdownoramylolysisbroughtaboutbytheparasite’.

Aswecansee,ourtrophobiosistheorytotallycoincideswithDufrenoy’sobservations:thequantityofphenoliccompounds, incorrelationwiththepaucityofaminoacids,bringsabout resistance.This resistance isnotduetoanytoxicitytotheparasites,buttoalackofnutritionalelements.Thisis,forexample,thecasewiththeN/phenolsbalance,whichexplainsthesensi-tivityofthemaizeplanttoHelminthosporiosis.Thissensitivityisrelatedtothevalueof thenumerator- inotherwordssolublenitrogenousproducts,thefundamentalnutritionalelementsthatwewillencounterthroughoutthisstudy,whichencouragethedevelopmentofvariousparasites.

4. Other environmental factors that have an effect on the metabolism, and thus the resistance of the plant

We have deliberately left to the end the cultural impacts capable ofinfluencingplant physiology and resistance.Manhas not alwaysweighedcarefullytheconsequencesofhisactions,whenitcomestotheresistanceofplants.Theseconsequencescanbeseenintheimpactsofthenew‘intensive’methodsofagriculture,particularlyinthecasesofcerealproduction,arbori-culture,andviticulture.Thefactorsthatseemtousmostimportantare

• theuseofnewchemicalpesticides;• techniquesoffertilisation.• thetechniqueofgrafting(lessimportant).

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In theyears sinceWorldWarTwo, thefirst twoof thesepracticeshaveundergone huge changes, with the arrival of new synthetic products forphytosanitary uses and the increased use of artificial fertilisers, notablynitrogen.

Theintroductionhasalreadyexploredtheroleplayedbyartificialpesti-cidesinsettingoff‘biologicalimbalances’suchastheapparently‘abnormal’developmentofdiseaseandinfestationofinsects,mites,nematodes,etcthatdamagecrops.Wewillthereforebeginbyexamininginthenextchaptertherepercussionsthatpesticideshaveonaplant’sphysiology,particularlyontheprocessofproteinsynthesis,which,aswehavealreadyseen,isfundamentaltodiseaseresistance.5

Notes1 FromChaboussou:Les Plantes malades de Pesticides,Débard,Paris,19802 Theseincludedownymildewofcabbage(Peronospora brassicae),downymildewof

beet(Peronospora schachtii),andtobaccobluemould(Peronospora tabacina).3 Plasmmodiophora brassicae.4 Fusarium(L).

37 The Repercussions of Pesticides on the Physiology of Plants, and the Consequences for their Resistance to Parasites

Chapter 3

The Repercussions of Pesticides on the Physiology of Plants, and the Consequences for their Resistance to

Parasites

I. The participation of pesticides in the metabolism of the host

plant

Apartfromthephenomenaofburnsorofphytotoxicity,causedbycertainpesticides,whichpreventstheirbeingsoldcommercially,thelessspectacularside-effectsofphytosanitaryproductsonplantphysiologyhavescarcelybeenconsidered.Thereareseveralreasonsforthis.

First,theproductsused(whetherfungicidesorinsecticides)werethoughttoactonly ‘on the surface.’Among these, forexample,werecopper-basedproductsand‘ingestion’insecticides,suchasarsenic-basedones.Therewasthusbelievedtobenoneedforconcernaboutachemical’spenetrationintoatreatedplant’stissues,oraboutanyeventualreactionoftheplant.

Nevertheless, with the development of ‘systemic’ insecticides and anti-fungalproducts,and theuseofherbicidesonavast scale, thequestionoftheireffectsonplantshasbecomemoreandmoreurgent.

The previous chapter shows that the relations betweenplant andpara-sitearenutritionalinnature.AsCollectif(1979)hasstressed,‘Aparasiteispledgedtotheplantinthenameofthenutritionoffereditbythatplant.’Ifwealsotakeintoaccountthecaseofherbicidesandtheir‘reduced’selectivity,weneedtobecomemoreandmoreurgentlyconcernedabouttheimpactsofpesticidesonthephysiologyofplants.

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We will study these effects chiefly with respect to the ratio of proteinsynthesistoproteinbreakdown.First,though,wewillbrieflyconsiderhowapesticidepenetratesintotheplanttissues.

II. Pesticidal penetration into the plant

Theuseoffolialfertilisersandherbicides,nowcommonplaceinagricul-turalpractice,showsthatplanttissuescaneasilybepenetratedbynumerouschemicals.The‘overleaping’ofbarrierssuchasthecuticleandcellwallsbyliposoluble compounds is facilitatedby the lipids in the cuticle andwalls.Thisexplains,forinstance,howametallicsaltsuchashydratedcopperoxide(fromapplicationsofBordeauxmixture)canpenetrateintotheleaf,aswasaffirmedlongagobyMillardetandGayon(1887)anddemonstratedmorerecentlybyStrauss(1965).

Thisexplainsdifferencesinsensitivitytopesticides,accordingtotheplantspecies or variety. Penetration by sprays depends on the thickness of thecuticleaswellasonthedistributionandnumberofstomata.Butperhapsitistheosmoticpressureinsidethecellsthatchieflyregulatesthispenetration.Whenthecellularsapisisotonicorhypertonicinrelationtothespray,thereisnodangerofburning,forpenetrationisimpossible.Whenthesapishypo-tonic,ontheotherhand,changesaremorefrequent,duetoplasmolysisofthecells.Forinstance,Menzel(1935)wasabletoshowthatcertainvarietiesofpearandappletreewithahighosmoticpressure(30-38atmospheres)arealmosttotallyimmunetocoppersprays,whereasothervarietieswithalowosmoticpressure(5.3to13.7atmospheres)areseverelyaffected.

Thisexplainsvariationsinpesticidepenetration,accordingtothephysio-logicalstateoftheplantatthetimeoftreatment.Thisstateinturndependsonabiotic factors, tissueage, and thenatureof thenutritionof theplant.Thus light,bypromotingmaximumopeningof thestomata, increases thepermeability of the leaf. An increase in temperature can have the sameeffect:inwarmweather,forinstance,nicotinetreatmentresultsinburning,whereasthisnowoutmodedpesticidehasnophytotoxiceffectwhenappliedinperiodsof lower temperatureandweakersunlight.Thesameapplies tosulphur.


Likewise, 2,4-Dpenetratesmuch faster into leaves of the bean plant indaylightthaninthedark(Sargent,1964).

Finally,senescentplantsallowgreaterpenetrationbychemicals.

Ultimately,ofcourse,thechemicalnatureofthepesticidealsoplaysarole.While,forexample,organophosphatessuchasparathiondisappearrapidlyfromthesurfaceofleavesandpenetratethemalmosttotallywithinjusttwodays, substances such as chlorinated chemicals and carbarylpersistmuchlonger.Withrespecttotheirrelationwiththeplant,wecansayingeneralthatartificialorgano-chemicalshaveaveryspecialaffinityforplanttissues.TheradicalC6H5inaformulamakesfatssoluble(liposolubility).TheradicalsOH,COOH,SO2andNH2inducehydrosolubility.Cl,aconstituentofmanymodernfungicides,islinkedwithpersistenceoftheproduct.Weshallreturntothispointlater.

Anotherimportantpointaboutpesticidesistheircirculationanddiffusionthroughtheplant.Thiscanhappenintwoways:

• thechemicalcanbetransportedtothecellsbytheapoplasticpathway.Thechemicalpassesthroughthecellwall(the‘gap’betweenthewallandcuticlethatgivessolutesaccesstothelivingcell).Thismeansthatthepesticideiscarriednotonlythroughthevesselsofthewood,butalso through the spaces between the cells.Numerous chemicals arediffusedinthismanner.

• transferofthepesticidecanjustaseasilytakeplacefromcelltocell.Thisisthesymplasticpathway.Itpenetratestheplasmodesmes,thoseporesthatalloweasyexchangesfromcelltocell.

Allthiscanleadtodisruptionsatthelevelofcellularactivitiesandwillbediscussedlater.

Astothewaysthatpesticidesgainentry,wecansaythatallthepartsoftheplantareinvolved.Penetrationcaninfacttakeplace:

• through the leaf,duringtraditionaltreatmentswithinsecticides,fungi-cidesand,morerecently,acaricides;

• alsothrough the roots,asaconsequencenotonlyofpossibledisinfec-tionofthesoilagainstnoxiousinsectsorpathogenicfungi,butalsooffall-outfromfolialtreatments(herbicides,fungicidesandinsecticides).Thisfall-outhasamuchgreaterimpactthanonemightatfirstsuppose.

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Researchershavebeenstruckbythedrasticconsequences,suchassterilisa-tionofthesoilaftercuprictreatments,oreventheeliminationofearthwormsbydithiocarbamates.Buttherearealsomoreinsidiousrepercussions,suchasrenderingacropsusceptibletoparasites.Theinsidiouseffectstakeplace:

• through the seeds,asaresultofcoatingthemagainstbothdiseasesandinsects thatposeadanger to the seedlings.These indirect repercus-sions,throughtheireffectsonthephysiologyoftheplant,canbeeitherharmfulorbeneficial.

• through the trunk and main branchesoffruittreesand,inparticular,thegrapevine.Thisisafourthmeansofpenetration,onenotgenerallytaken intoaccount.Penetrationhere takesplaceduring theapplica-tionofbothfungicidesandinsecticidesduringwinterorpre-pruningtreatments.

Ithasbeenshownthat,eveninwinter,afruittreecanabsorbconsiderablequantitiesofachemicalsprayedonitsbark.Itisnotsurprising,then,thatpesticidesappliedtoatree,eveninwinter,canhaveaneffectonthephysi-ology,andthusontheresistanceoftrees.Whatismore,Willaume(1937)wasabletoshowthatanthraceneoilshaveastimulatingeffectontreegrowth.Incertaindilutions,theseanthraceneoilscanclearlyacceleratethegerminationofgrainsofwheat.Wecanrightlyaskwhetheracupricapplicationin lateautumnagainstcryptogamicorviraldiseaseswouldnotactinthesameway.Itcouldworkindirectly,inotherwords,throughthebeneficialeffectsofthetraceelementcopperonthephysiologyofthefruittree.Weshallreturntothesubjectofhowtraceelementsactontheplant.

Fornow,wewill continueour investigationof the effectsof thegrowth substancesthatweknowfairlywell.Asweshallsee,thesearenotunrelatedtotheeffectsofcertainpesticides,althoughthelatterareneverusedforthesameends.


III. The repercussions of growth substances

a) Growth substances and plant metabolism

Amongthegrowthhormoneswefind:

• auxines,whichhaveaspecificeffectongrowthitself;• cytokinins,whichacceleratethecells’multiplicationrate;• gibberellins,whichhavemultiplefunctions:accelerationofgermina-

tion,increaseofamylaseintheendosperm,andactivationofprotease(whichresults intheformationof tryptophan,precursorofß-indol-aceticacid,orIAA).

IAA is therefore formed in tissues that are still growing, above all inthe extremities of the roots. This is the auxine that causes roots to growdownwards.

Asforthecytokininssuchaskinetin,derivedfromadenine,theseplayaroleinthegrowthanddifferentiationofcells,aswellasinotherinterestingphysiologicalfunctionssuchastheinhibitionofsenescence.Theinteractionsof auxins and cytokinins control the differentiation of tissues previouslyundifferentiatedintherootsandshoots.

Althoughuntil1956scientistswereonlyawareoftheexistenceofauxins,gibberellins, and cytokinins, they suspected the existence of anotherhormone,onethatcouldbalanceouttheeffectsoftheothers.Infact,in1965theydiscoveredabscisinII incotton,togetherwithdormininmaplebuds(whichpreventstheiropening).Thesehormoneshavethesamestructure,amoleculethatiswidespreadintheplantkingdom:abscisicacidorABA.

Inthemajorityofcases,ABAcounteractstheeffectsofgrowthhormones:itisclearlythe‘modulator’whoseexistencehadbeensuspected.Asaresult,agronomistshopetobeabletoinduceleavestofall,preventpotatoesfromgerminating,encouragetheripeningoffruit,etc.Infact,atacellularlevelABAactivatescertainamylases,bringingabout thedestructionofstarchesinamyloplasts.Italsoinhibitsthesynthesisofribonucleicacid,leadingtoaconsiderablereductioninthequantityofribosomes,whicharerequiredforthesynthesisofproteins, these ‘ultimateelementsof theexpressionof thegenes.’

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ABAthusblocksthesynthesisofproteins(whilecytokininshavetheoppo-siteeffect).ThisblockingcausesareductioninthetotalamountofcellularRNA.Thisconfirmsatcytological levelthatanexcessofABAleadstothedisappearanceofribosomes.

Tosumup,ABAhasa regulatoryrolewithregard togrowthhormonesandanantagonisticrole(directlyorindirectly)atthelevelofcertaingenesofsynthesis.Thisroleismediatedbyenzymes.

Havingbrieflydefinedplantmetabolismastheachievement,primarily,ofadegreeofequilibriumamongantagonisticsubstances,wearebetterplacedtounderstandtheeffectsofthegrowthsubstances.

b) The effects of growth substances on the biochemical state of plants and on their resistance to parasites

Variousgrowthsubstances,suchasgibberillicacid,ß-indolaceticacidand2.4-D,havebeen tested in controllingplantdisease.Theyhavebeenusedagainstbothpathogenicfungiandviraldiseases.Theresultshavebeenvariedandoftencontradictory,withoutresearchersbeingabletogivereasonsforthis.Wewillattempttoclarifythemechanismoftheseeffects.Tobeginwith,wewillanalysetheresultsofattemptstocontrolPhytopthora cactorumonthestrawberryplant.

Intheirstudyentitled‘TheInfluenceofSeveralGrowthSubstancesontheStrawberryPlant’sSusceptibilitytoAttackbyPhytopthoracactorum,’MolotandNourrisseau(1974)concluded:

• Under glass, dipping pre-refrigerated1 plants in different growthsubstances, justprior toplanting and inoculationwithPhytopthora,elicitsavarietyof responses in termsofmanifestationof symptoms.Thus,atconcentrationsof10-6orabove,

• gibberillicacid,naphthaleneaceticacid,andindolaceticacidpromotedisease;

• tri-iodo-benzoicacids,onthecontrary,reinforceresistance;• abscisicacid,ataconcentrationof10-7,increasesthedamagecaused

byPhytopthora,butceasestohavethiseffectasonemovesawayfromthisconcentration.


Theauthorsof thisresearchweretherefore ledtothe justifiableconclu-sion: ‘A relationship seems to exist between the physiological state of thestrawberry,subjecttorathercomplexhormonalbalances,anditsresponsetoPhytopthora cactorum.’Theiranalysisstopshere,withoutgivinganyexpla-nationofthediversityofresponsesbroughtaboutbythedifferentsubstancestested.Wewilltrytogofarthertowardexplainingthesephenomena.

Withregardtogibberellin,AltergotandPomazona(1963)emphasizedthattheeffectsofanypesticideorchemicalwhatever,whenappliedtoaplant,dependonseveralfactors.Themostimportantare:

• the dosage applied;• the ecological conditions:light,humidity,temperature,etc.;• the age of the plantoritspartsatwhichitisapplied;• the plant’s nutrition, aconcluding factor thathas so farbeen largely

overlooked.

Theauthorspointoutthatinorderforthegibberillintohaveapositiveeffect,theseconditionsshouldcorrespondtoa‘stateofacceleratedgrowth’:in other words, a state of optimum protein synthesis.We shall encounteranalogousphenomenawithcertainpesticides,forexampleDDT.

AsAltergotandPomazona(op.cit.)observe:‘Wecanconcludethatwhenaplanthasbeenstimulatedbygrowthsubstances,itrequiresrapidcomple-mentarynutritioninthosesubstancesthatareindispensableforthesynthesisofitsconstitutivecompounds.’

Thisiswhyvariousresearchersworkingwiththepotatoplant,suchasWort(1962),obtainedanincreaseinyieldonlywhentheyapplied2,4-Dalongwithspecific fertilisers,whether inthesoilat theroot level,or througha foliarspraymixedwith the growth substance.Wort (op. cit.) used chiefly traceelements,suchasironandcopper.Theseexperimentsshowed,onvariousvarietiesofpotato,grossyieldincreasesof5-45%,alongwithincreasesinthesizeofthetubers.

AsWortnotes, inpassing: ‘Whilethecausesof increaseinresistancetodiseasearenotasclearasthefavourableeffectonyield,itisclearthatthegeneral tendency is favourable.’Thisobservationseemstoagree fullywithourowntheorythatresistancetodiseaseislinkedtostimulationofproteinsynthesis.Infact,thetubersofpotatoestreatedwithamixtureof2,4-Dandtrace elements have, in comparison with controls, shown lower levels ofreducingsugars.

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Inthesecondplace,likeAltergotandPomazona,Wort’sfindingsshowthatthedifferencesineffectcorrespondtothetimingofthetreatment.Anintervalofonemonth(July23-August24) in treatingpotatoeswith2,4-Dcausesdifferencesintheamountsofthedifferentcategoriesofsugarscontainedinthetubers.Thereducingsugarsbecomemoreabundantinpotatoestreatedlaterintheperiod,attheendofAugust.

Weshallreturntotheimportanceofthestageofinterventionwithpesti-cidetreatments,fromtheperspectiveoftheireffectontheplant’sphysiology,inrelationtothephysiologicalcycleoftheplant.Thisinquiryisjustifiedbytheimpactofthetreatmentsonthebalancebetweenauxinsandgibberellins.Thisbalancecaneasilybeupset,forgoodorforill,byapplicationofartificialgrowthsubstancesor,asweshallseebelow,ofanykindofpesticide.

We shall now attempt an explanation of the diverse responses toPhytophthora cactorum in the strawberry, as recorded by Molot andNourrisseau(op.cit.),accordingtothedifferentgrowthsubstancesthatweretested.

WeshallfirsttakethecaseofabscisicacidorABA,whichataconcentrationof10-7 increasesthedamage.Theeffectsofthissubstancearewellknown:theyactessentiallyasinhibitorsofthesynthesisofRNA.Theoutcomeisaconsiderablereductionofthelevelofribosomes.Now,asweknow,ribosomesaredirectlyinvolvedinthesynthesisofproteins.ABAblocksthesynthesisofproteins,apparentlybyactingon themessengerRNA.Thisproducesacorrespondingincreaseinthelevelsofsolublesubstancesintheplanttissues.This favourablenutritionaleffectonthepathogenexplains the increase indamagebytheparasiticfungus.

Thereisgoodreasontoaskwhetherasimilarprocessmightnotbeinvolvedwhensusceptibilitytothediseaseincreasesaftertheplantsaretreatedwithgibberellicacid,naphthylaceticacid,andindolaceticacid.

Likewise,weneedtostudytheindirectmodeofactionoftri-iodo-benzoicacid.Incontrasttoothersubstances,itreinforcesresistance.However,foreachsubstancewemustineachcasetakeintoaccountthephysiologicalstateoftheplant.Forexample,astrawberryplantthathasbeeninarefrigeratorforaconsiderableperiodoftimehastoallappearancesaslowmetabolism,tosomeextentresemblingasomewhatsenescentplant.Underthesecondi-tions,therefore,tri-iodo-benzoicacidmayshowapositiveeffectonproteinsynthesisandthusourconceptionofresistanceAlltheothersubstances,bycontrast,yieldednegativeresults.


Wethereforecanexplaintheoftendiametricallyopposedrepercussionsofthesubstancesthathavebeensystematicallytested-bytheirbiochemicalandnutritionaleffects,nottheirtoxicitytothepathogenicagent.

Withregardtogibberellin,VanOverbeck(1966)notedthatopinionwasmovingtotheideathatplanthormonesactonthesystemofnucleicacidssomewherebetweentheDNAandthemessengerRNA.Suchaninfluencewould therefore control enzyme formation and, as a consequence, thebiochemistryandthephysiologyoftheplant.

Gibberellinwouldtherefore,byitsactiononthesynthesisofmessengerRNA,stimulateamylaseinaccordancewiththefollowingdiagram:

Actionofthegibberellicacid

DNA messengerRNA aamylase.

Throughitsactionontheproteolyticenzymes,gibberellincancausetheformationoftryptophan,theprecursortoIAA.Auxinandgibberellincanactsynergistically.Ontheotherhand,weknowthatthefunctionsofhormonesoverlap.Itis,however,theinitialstateoftheplantthatappearsabovealltodeterminethenatureoftheeffectsofaspecificgrowthsubstance.

Gibberellin, for example, stimulates the formation of reducing sugarsin potatoes in a dormant state, according to VanOverbeck. This processpromotesproteinbreakdown.Wecanthereforeposethequestion:towhatextentmightthissamesubstanceactsimilarlyontherefrigeratedstrawberryplant, whosemetabolism has been inhibited by the cold? Could it bringaboutan increase in the soluble substanceswhichnutritionally sensitiseaplanttoPhytophthora?

If,ontheotherhand,gibberellinhaspositiveeffectsonproteinsynthesis,dependingontheinitialstateoftheplant,thesameistruefordiseaseresist-ance.Inthisway,RodriguezandCampbell(1961)wereabletodemonstratethat applyinggibberellin to theapple tree, thebeanplant, and thecottonplantbothstimulatedthegrowthoftheplantandalsoreducedpopulationsofTetranychus telarius.

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Applyingdosesof10ppmofgibberellintoappletreesincreasednumbersofPanonychus ulmi,whilehigherdoseshadtheoppositeeffect,decreasingnumbers.Thesedifferentpopulationlevelsshowsignificantcorrelationswiththelevelsoftotalsugarsintheleaves.

Populationsofthetwospecies,moreover,showapositivecorrelationwiththenitrogencontentoftheleaves,whichisinturndependentupontheactionofgibberellinatagivendose.

Likewise,RodriguezandCampbellsuggestthat,generallyspeaking,thereis an optimum level of reducing sugars for the development of parasites,when it come to a plant’s susceptibility to attacks by disease andnoxiousinsects.This situationcanbe slightlymodifiedby taking intoaccount thelevelofnitrogenandthe interactionof thesetwonutritionalsubstances,apointthatwasmentionedaboveandwhichwewilldiscussindetaillater.

Hukusima(1963),lookingattheproliferationoftheaphidMyzus malis-inctusonappletreestreatedwithvaryingdosesofgibberellin,cametothesameconclusion.Whilethemaximumproliferationresultedfromadosageof50ppm,aconsiderablereductioninfecunditywasregisteredwithadoseof100ppm.Thisledtheauthortoconcludethatthereisprobablyanoptimumlevelofreducingsugarsandtotalsugarsforthedevelopmentofaphids,aswellasofmites.Weshallreturntothissubjectofaphidproliferationoncerealcropsandthedevelopmentofviraldiseases.Forthemoment,however,weshallexamineinsectproliferationbroughtaboutbygrowthsubstancesasaresultoftheireffectsonplantbiochemistry.Wewilllookparticularlyatthemostwidelyusedsyntheticgrowthhormone,2,4-D,and itsclose relative,2,4,5-T.

Repercussions of 2,4-D and 2,4,5-T.

Withregardtothedevelopmentofdisease,ithasbeenfoundthat2,4-Dhascontradictoryeffects.Afterallthatwehaveseenabove,thisshouldnotsurpriseus,sincetheseeffectsdependupontheinitialstateoftheplantanditsultimatebiochemicalstate.Theyalsodependuponecologicalconditions,theplant’snutrition,andthenutritionalrequirementsofthespecificparasite.


Ithasbeenshownthattreatingwheatwith2,4-Dpredisposesittoseriousattacks of Helminthosporium sativum. In contrast, thanks to the sametreatment of 2,4-D on the broad bean plant, Mostafa and Gayed (1965)obtainedanetanticryptogamiceffectagainstBotrytis fabae.Itseemsclearthatthis‘fungostatic’effecthasitsoriginintheactionofthechemicalontheplant’smetabolism.Analysesoftissuesamplesfromtreatedplants, infact,showedthat2,4-Dhadconsiderablyreducedthesugarlevelsoftheleaves.TheauthorsconcludedthatthisprocessseemedtointerferewiththenormaldevelopmentandpotencyoftheBotrytis.

Wewouldaddthatthistoohasanutritionalcause,giventhatthefungusin‘greymould’hasparticularlyhighnutritionalrequirementsforsugars.Thisexplains,besides, the inverseeffects:dithiocarbamatessuchasmanebandzineb, which are well-known for promoting the development ofBotrytis,particularlyonthegrapevine,produceanincreaseinthelevelsofsugarsintheleaftissues.

Theexplanationfortheseconvergentphenomenaliesinthefactthatbothdithiocarbamatesand2,4-D,appliedrepeatedlyoratspecifictimes,inhibitproteinsynthesis.Thiscausesanincreaseofsolublesubstancesinthetissues,whichmaketheplantnutritionallysusceptibletoparasiticfungi.

The same processes may equally apply to proliferation of insect pests.MaxwellandHarwood(1960)wereabletoshowthattreatingbroadbeanswith 2,4-D produced a clearly elevated rate of reproduction in the aphidMacrosiphum pisum. This fact appears to be related to an increase in thesapof various freeaminoacids suchasalanine, aspartic acid, serine, andglutathione. In this case too, reducing sugarsappear toplaya role in theaphid’sfecundity.(Weshallreturntothispointlater.)

However,parallelsappearbetweentherepercussionsofcertainpesticides.

Smirnova (1965) found that the reproduction ofAphis fabae on flowerstalks treatedwithDDTwasat itsgreatestbetweeneightandfifteendaysaftertheapplicationofthepesticide.Accordingtotheauthor,thisincreaseinegglayingcorrespondedwithanincreaseinnon-proteinnitrogeninthetreatedplants.Furthermore,theflowerstalkstreatedwithDDTshowedanincreaseinsugarscomparedwiththecontrolplants.

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Theaphidlarvaefeedattheplant’sexpensewherethesaphashighlevelsof soluble substances (nitrogen and sugars), thus showing a balance thatincreasestheir fecundity.Inotherwords, inthiscase(as inallothercaseswheretheplant’sresistance isundermined)theparasiteproliferateswhereproteinbreakdownpredominatesinthehostplant’smetabolism.

Theharmfulside-effectsofpesticidesarenotconfinedtosuckinginsectssuchasaphidsandmites.Theyextendtoothernoxiousinsectsthatdonotspecifically feedoff the sap. Ishii andHirano (1963) showed that the riceborer Chilo suppressalis (a lepidopteran) multiplied on rice treated witheither2,4-DorDDT.

Theseresearchersshowedclearlythatthiswasduetoindirectnutritionaleffects.Treatedplantsincreasedtheirbioticpotentialbyofferingthelarvaeabetterdiet,through a higher level of nitrogenous elements.

Interestingresearchhasbeendoneontherelatedchemical2,4,5-T(2,4,5trichlorophenoxyaceticacid).Thegoalwastoascertaintheoptimumdosage,in the lightof the increase in yield it produces.The researchunderscoresclearlythegreatimportanceoftheeffectsthataplant’snutritionhasonitsmetabolismandthusonitsresistance.Yurkevitch(1963)demonstratedthat2,4,5-T,appliedtothetomatoplant,reducedleaflossandacceleratedgrowthofthefruit.Thesebeneficialeffects,however,arisewhenthereisoptimumfertilisation.Thebestresultsareobtainedbyaddingcertaintraceelements,suchasboronormanganese,tothegrowthsubstance.Notonlyisthereanincreaseinyield;inaddition,treatingtheplantwithamixtureof2,4,5-Tandtraceelements suchasmolybdenumbringsan increase indrymatterandvitaminCcontentinthefruit.Inthisway,animprovementisalsoachievedinthequalityoftheharvest.

The author insists on achieving an optimum balance of the fertiliser inrelation to the stimulating effect of the growth substance. While tomatoplantstreatedwithamixtureof2,4,5-Tandboronproducedahigheryieldand better quality fruits, a concentrated treatment with just one of themsuppressedthegrowthoftheplants.Wewillhavetoreturntothissubjectof trace elements. Suffice it to say at this point that they formpart of thecomposition of enzymes and, because of this, they affect the direction ofoxidative-reductiveprocesses,promotingthetransportofcarbohydratesandactingontherespirationrate.


Weshouldnotbesurprisedifweencountersimilarphenomena,whetherbeneficialorharmful(as ismostoftenthecase),accompanyingtheuseofvariousphytosanitarychemicalssuchasinsecticidesandantifungals.Untilnow, little thoughthasbeengiventotheireffectsonthephysiologyof theplant,aslinkedtoitsresistance.

c) The effects of maleic hydrazide

Drawing up a balance sheet of the effects of maleic hydrazide on thebiochemistryofthetreatedplant,Wort(1962)statesthatwhenincorporatedintothesandinwhichbarleyandwheataregrown,maleichydrazideleadstoaconsiderableincreaseinlevelsoffreeaminoacids,particularlyglutamine,intheleaves.Fivedaysaftertheapplication,thetreatedleavescontainfivetimesmorefreeaminoacidsthanthecontrolplants,andafterfifteendays,fifteentimesmore.

Similar changes occur with sugars. When applied to maize, maleichydrazidereducesthelevelsofglucose,butitcanincreaselevelsofsaccha-rosebyasmuchasthirteentimes,comparedtocontrols.

Insummary,althoughtheserepercussionsofmaleichydrazidedepend,aswithallchemicals,ontheinitialstateoftheplant,theycanbeexplainedbyadualphenomenon:• stimulationofphotosynthesis,ontheonehand;• inhibitionofproteinsynthesis,ontheother.

Certaintherapeuticeffectshavealsobeenattributedtothesebiochemicaleffects.Horsfall andDimond (1957), reasoning from the fact thatmaleichydrazideincreasesthesugarlevelsoftheleaves,concludedthatthischem-icalshould increasediseasesrequiringhighsugar levels,suchasrustsandOïdium,anddecreasethosethattoleratelowlevelsofsugars.

Maleic hydrazide does in fact decrease the susceptibility of the tomatoplanttoAlternaria.Thesameauthorsthinkthat,inprinciple,itshouldalsorenderthefoliagelesssusceptibletoHelminthosporium sativum.

In addition, Sprau (1970) showed that applying maleic hydrazide topotatoes inhibits thedevelopmentof tumoursproducedbyAgrobacterium tumefaciensandSynchrytium endobioticum.Spraustressestheimportanceofstudyingtherelationsbetweenhostandparasite.Withregardtotheupsurgeofbacterialdisease,weshallseepreciselywhatistheroleplayedbythenewchemical products in the harmful phenomena that occur after the use oftheseproducts.

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Here,too,weshallfindaconfirmationoftherelation:proteinsynthesisresistance,whileproteinbreakdownsusceptibilitytoattackfrombacteria.

This is theprocess,nutritional innature, that enablesus toexplain theresults of Molot and Nourrisseau (op. cit.), obtained from Phytopthora cactorum,var.fragariae,usingvariousgrowthhormones.

Insum,theseresultsconfirmthat:

• theplant-parasiteinteractionisnutritionalinnature;• repercussionsfromthesamepesticidewillvaryaccordingtotheinitial

stateoftheplant.

Thereisaninevitableinterference,infact,betweentheartificialgrowthhormones and the natural hormones that govern the plant’smetabolism.Thismakesitvitaltotakeintoconsiderationtwoimportantfactorsrelatingtoselectionofthebesttherapy:

• thecriticalstagesofmetabolism,particularlythefloweringperiod;• theplant’snutrition,whichdependsnotonlyongenetic factorsbut

alsoontheclimateandartificialfactors,suchasfertilisation.Thiscanbemineralororganic,andmusttakeaccountofthe‘availability’ofthetraceelements.

Itistheimportanceofthesedifferentfactors,whichhaslargelygoneunno-ticed, thathasmade the effectsof the various commonly employedpesti-cidesincomprehensiblehitherto.Hereweintendtobeginthisinvestigation,commencingwithchlorinatedchemicals.

IV. The effects of chlorinated chemicals, especially DDT

Because of their persistence and their transmission through the foodchain, these chemicals are now banned from agricultural use inmany oftheindustrializedcountries..2However,likethegrowthsubstanceswehavejust examined, they remain interestingbecauseof their impactsonplantbiochemistryandphysiology,andthusonresistancetodisease.Theirimpactonbothisusuallynegative.

Basedonstudiescarriedout,itappearsthatDDTinparticularactsasagrowthsubstanceforplants,comparabletonaturalgrowthhormones.


ChapmanandAllen(1949)madeuseofthiscomparisontocharacterisetheeffectsofDDTonthevariousplantstheytested.Theseeffectsvary,ofcourse,according to thebotanicalnatureof thespecificplant,andalsoaccordingtothedosageapplied.Highconcentrationshavephytotoxiceffects,suchasstunting,deformities,chlorosis,andnecrosis,whileat lowdosessuchsideeffectscandisappear,tobereplacedbygrowthstimulation.

Phenomenaof‘remote’effectsarealsoobserved,althoughthesemustnotbeconfusedwith‘systemic’effects(thetransportationofthepesticidethroughthetissuesoftheplant).ChapmanandAllenobservedthatapplyingDDTtotherootsandlowerleavesofaplantresultedinstimulationofthehigherpartoftheplant.Fromtheirobservations,theauthorsconcludedthattheeffectsofDDTonplantscloselyresembledthoseofcertainplanthormones.

Thisexplainswhy,withregard tobothdiseaseand insectattacks,DDTcanhaveeitherpositiveeffectsor,moreoften,negativeones.InthecourseofthepreviouschapterwenotedthatDDTrenderskhapliwheatmorepronetorust(Johnson,1946).TheexplanationforthiswasgivenlaterbyForsyth(1954): ‘DDTalters thewheat’smetabolisminsuchawayas tomakefreeaminoacidsandsimplesugarsaccumulateintheleaves.Thisphenomenonappearstobeduetoaninhibitionofsynthesisofproteinsandcarbohydrates.’(Johnson,op. cit.)

Thiswould appear to explain the swarmsof various insect pests in thewake of treatment of crops with DDT or similar chlorinated chemicals.Theseoutbreaksarenotdue,asthe‘classic’viewstillholds,todestructionoftheinsects’naturalpredators.

Forexample,HuffakerandSpitzer(1950)investigatedthevalidityofthislasthypothesis.Theoutcomeoftheirstudieswasthat,onthepeartree,thenaturalpredatorsprovedmoreabundantontreestreatedwithDDTthanonthecontrols.

Infact,astheyconcluded:‘TheincreasedpopulationlevelsbroughtaboutbyDDTdemonstrate thatDDTcan lead to an increase in thenumberofPanonychus ulmigreaterthanthatonthecontrols.Althoughthereasonsforthisareunknown,itcannotbeexplainedonthebasisofnaturalpredators.’(Incertainexperiments, thepopulationofP. ulmionpear trees increasedtwelvefold.)

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Forhispart,Fleschner (1952) confirmed thefindingsofChapmanandAllen.He found thatDDTapplied to citrus causedchanges in the leaves,makingthemlessresistanttoattacksbymites.Thisstageofreducedresist-ancepersistedintheleavesforaperiodofmorethansevenmonths.

Moreover, Fleschner also showed that this reduced resistance is ‘trans-mitted’fromthelower,treatedleavestotheupper,youngerones.Attheendof46days the leavesabove those treatedwithDDTcarriedasignificantlylargernumberofeggsthanthelowerones.

Thissuggeststhatinthesecircumstances,DDTbehaveslikeahormone.Itseemstohavehormone-likeeffectssimilartothoseobservedbyForsythinwheat. It inhibits protein synthesis, leading to an accumulation of freeaminoacidsandreducingsugarsintheplanttissues.Thisphenomenon,byitsnutritionaleffect,permitsthemitestogrowinnumber.

Similar resultswere obtained by Saini andCutkomp (1956) in relationtoproliferationofTetranychus telariuswhentreatingtherunnerbeanwithDDT.Theauthorsconcludethatthisstimulationisindirectinnature,‘arisingfromaphysiologicalchangeinthehost-plant.’Theincreasesinreproductionareproducedwhenthereisacertainbalanceofnitrogenoussubstancesandsaccharose.

We should recall that, for bothPanonychus ulmi on the grapevine andTetranychus urticaeonthebean,wehaveshownthatDDT,alongwithotherpesticidessuchascarbarylandcertainphosphoricesters,hasthenutritionaleffect of increasing the mite’s biotic potential. It increases fecundity andlongevity,shortenstheevolutionarycycle,anddistortsthesexratioinfavouroffemales(Chaboussou,1969).

However,wedonotwishtoendthissectiononDDTwithoutmentioningthecaseofsoiltreatmentsandtheirunforeseenside-effects.KlostermeyerandRasmussen(1953)treatedsoilwithvariouschemicals(DDT,lindane,HCH,chlordane,andaldrin)invaryingdoses.Whentheylaterplantedpotatoes,they found thatplants growing in the soils thathad received theheaviestdoseswerefiercely attackedbyTetranychus bimaculatus. In the end theseplantswerealmostcompletelydestroyed.Afterpointingoutthatthemites’predatorswerefewinnumber,theauthorsconcluded:‘Itislikelythatthesedifferences innumbersofmitepopulations,duetotheuseof insecticides,hadtheirsourceinthenutritionandcompositionoftheplant.’


WithregardtothephysiologicalconsequencesofDDT,wenotealsothatKamal(1960)hasshownhowDDT,like2,4-D,actsonthedifferentformsofnitrogen(nitrogenammoniacandaminonitrogen),accordingtotheageoftheleaf.Thisjustifiesthehypothesis,saysKamal,‘thatusinginsecticidesandfungicidesonthemetabolicactivitiesofthetissuesofthehostplantcanaffecttheresistanceoftheplant.Itisalsooneofthepossiblecausesoftheoutbreakof‘peardecline,’rampantatonepointintheUSstateofWashington.’ThisdeclineisnowbeingdiscussedinFranceinrelationtoproliferationofpsyllids,whichobserversareunabletoexplain(KamalandWoodbridge,1960).Weshallreturntothesubjectoftheeffectsofsyntheticpesticidesinthechapterdedicatedtoso-called‘intensive’cultivationofgrapevinesandfruittrees.

Nowweshallturntotheimpactsoforgano-phosphates.

V. Side effects of organophosphates

Sincephosphatepesticideswerefirstputtouse,variousresearchershavenoted,apartfromthephenomenonofburning,diverseimpactsofaphysio-logicalnatureontreatedplants.Someoftherepercussionsarebeneficial,forinstanceincreasesinyield.Inthecaseofcotton,yieldincreaseshavebeenrecordedasaresultofweeklyapplicationsofamixtureofToxapheneandDDT.However,theinterestingpointtonotehere(becauseitconfirmsafactmentionedabove)isthatsuchpositiveeffectsonproductiononlyoccurifthetreatmentbeginswiththeappearanceofthefirstflowers,butnolater.Thisunderlinesoncemorethemajorimportanceoftheinitialphysiologicalstateoftheplantforthefinaleffectsofthechemicalapplied,asaresultabovealloftheauxinlevelsofthetissues.

In fact, as with growth substances and chlorinated pesticides, thebio-chemicalrepercussionsoforgano-phosphateproductshavetheirorigininthewaytheyinterferewithplantenzymes.Hascoet(1957)citestheworkoftwoJapaneseresearcherswhodescribethephysiologicaleffectsofcertainorgano-phosphateinsecticides,whichintheirviewarepreciselycomparabletothoseof2,4-D.

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Just as with growth hormones or chlorinated pesticides, tissue analysisrevealseffectsontheprocessofproteinsynthesis,whichcanbeeithernegativeorpositive,dependingonthecircumstances.Forthebeanplant,forinstance,Bogdanov(1963)notesthatparathionandthiometonbringaboutincreasesinfreeandboundaminoacidsintheleaves.Thelevelsofmethionine,valine,and phenylalanine are significantly increased, as are those of tryptophan,whoseimportancetoplantmetabolismscarcelyneedsmentioning.

Pickettet al.(1951)foundsomenegativeeffectsofparathiononthepeachtree,where it slowed downphotosynthesis in comparison to the controlsSimilar resultswere foundwhen treatingapple trees (RedDelicious)withethionanddiazinon.Theseorgano-phosphatesreducedthephotosyntheticpotential(thenetassimilationrate,orNAR).

Sucheffectsmaybecomparedwith theresultsobtainedbyNandraandChopra(1969),regardingtheeffectsofthiometonon‘groundnut’or‘groundpistachio.’Theoveralleffectofthiometonwastoincreasenitrogenlevelsintheleavesofthetreatedplants,bycomparisonwithcontrols.(Notethatthisincreaseinnitrogenlevelsisgenerallyfoundwithchemicalproducts,particu-larlyfungicides-orrather,anticryptogamics-andthatthisphenomenonliesattherootofaplant’ssensitisationtoitsvariousparasites,aswehavealreadypointedoutabove.)Inthesameway,andparalleltothisinhibitionofproteinsynthesis,thiometonincreasesthelevelsofreducingsugars.

This explains theapparentlyparadoxicalproliferationofmites,broughtaboutbywhat couldbe called a ‘boomerang effect’ of acaricideproducts.Several examples of this have been demonstrated in field and laboratoryexperiments.Forexample,Wafaet al.(1969)experimentedoncitruswithvarious acaricides (Thiocron, anthio, metasystemox), used alone, in amixture,oralternatingbetweenthetwo.Thesebroughtaboutincreasesinthenumbers of themiteEutetranychus orientalis, an effect that lasted forlongperiods.Theauthorsadd:

‘The harmful effect of the use of phosphorous acaricides, alone and inrepeatedapplications,canbeattributedtotheeffectthesechemicalshaveonthecompositionoftheplant.’


As for the biochemical mechanism of this phenomenon, the authorsconsiderittobelinkedtothefollowingfact:

‘In plants treated with these organo-phosphate acaricides - Thiocron,anthio,andmetasystemoxR-therewas,incomparisonwiththecontrols,bothanincreaseinsolublesugarsandadecreaseinpolysaccharidesintheleavesandstems.’

Onceagain,weseethattheplantismadesusceptibletomitesbyacaricidesthat inhibit the plant’s protein synthesis. We have stressed in our book,Plants Made Sick by Pesticides (Les Plantes Malades Des Pesticides),thefullimportanceoftherepercussionsofthevariousacaricidesusedtotreatfruittrees, as studied by Blagonravora (1974). Themost effective products, asonemightexpect,werethosewiththemostlong-lastingpositiveeffectsonproteinsynthesis,suchasdicofolandphosalone.

Inthecaseofthegrapevine,wehaveourselvesfoundthatparathion,whichbrings about a reduction in proteic nitrogen and an increase in reducingsugars,provokesthroughatrophiceffecttheproliferationof‘yellowspider’(Eotetyranychus carpini vitis)attheendoftheseason(Chaboussou,1969).

Allthesestudiesshowthatnumerousorgano-phosphatesinhibitproteinsynthesis, especially since they are used in repeated applications and atsensitivestagesintheplant’sgrowingcycle.Thisisthecauseoftheplant’sincreasedsusceptibility,notonlytosuckinginsectssuchasmites,aphids,aleurodes,and(soitseems)psyllidsbutalsotodiseases,fungalandother-wise,asweshallseebelow.Besides,thesenegativeeffectscouldalsoresultfromtheuseof‘fungicides,’aswillnowseedemonstratedthroughastudyoftheeffectsofdithiocarbamates.

VI. The effects of carbamates and dithiocarbamates

Carbamates,derivedfromcarbamicacid,anddithiocarbamates,derivedfrom dithiocarbamic acid, constitute a large group of artificial organicsubstances. Among these are ‘fungicides,’ including carbamates (benomyl,carbendazeme, thiobendazole) and dithiocarbamates (zineb, maneb,mancozeb),tonamebutafew,aswellas‘herbicides,’includingcarbamates(propham,chlorprophametc)anddithiocarbamates(nabam,for instance,whichisalsoafungicide).

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Aswiththecategoriesofpesticidesalreadyexamined,setbackshavebeenrecorded. Polyakov (1966) - who was perhaps the first to make the linkbetween theplant’smetabolism,whenalteredbypesticides, and suscepti-bilitytopests,notedthatusingzinebtoprotectpotatoplantsagainstmildewledtothedevelopmentofotherdiseases,particularlyviralones.Thissamecarbamate,whenusedonapplesagainstscab,stimulatesthedevelopmentofOïdium.Wehaveexperimentallydemonstratedthisresultonthegrapevine(Chaboussou, 1968). It has also been observed on apple trees on severaloccasionsinFrance,andwassubsequentlyconfirmedinBulgariabyVanevandCelebiev(1974).Thesetests,conductedwithcontrols,showclearlythatitwasaquestionofproliferationofthepathogenicfungus,notitsresistanceortheeffectivenessofthepesticide.Thisisafundamentalpointtowhichwewillbeobligedtoreturn.

Polyakovhasalsoshownthatasingletreatmentofacerealplantagainstrust(Puccina graminis tritici)couldinducea‘pseudo-resistance.’AsPolyakovconcluded,‘Oneoftheprincipalfactorsdeterminingaplant’sresistancetocryptogamicdiseaseisitsphysiologicalstate.’

Similarly, dithiocarbamates such as nabam applied to tomatoes lead tothedevelopmentof ‘greymould’orBotrytis,asdoesmanebalso(CoxandHayslip,1956).This‘unexpected’result,astheauthorscalledit,alsooccurswith strawberries.When these are treatedwith zineb orwith nabam-zincsulphate,muchmoreBotrytisdevelopsthanonthecontrolplants.Thisledtheauthorstoconcentratemoreonthissideeffectofdithiocarbamates:thatis,ontheincreaseintheplants’susceptibilitytoBotrytis.

Analysisof the leaveshas shown that somebuild-upof zinc is theonlyappreciable change in the compositionof the leaves. Inolder leaves, aftertreatment, thezinccontent is13 timeshigher thannormal, and inyoungleaves,3.5timeshigher.Astheauthors(CoxandWainfree,1957)pointout,itiswellknownthatanexcessoftraceelementscancauseimbalancesinplantmetabolism. In a precise comparison with the control plants, significantdifferencesinproteincontentswerenoted:plantstreatedwitheitherzineborwithamixtureofnabamandzincsulphatehadalowproteinlevelcomparedwithcontrols(Table3).


Table 3: Levels of protein nitrogen in strawberry leaves following various treatments, in ppm

Controls Zineb Nabam + zinc sulphate

3.18 3.08 3.06

Inotherwords,thehigherrateofproliferationofBotrytisonstrawberriestreatedwithzinebandnabamisduetoadecreaseinproteinsynthesis.Thisoffersyetanotherconfirmationofourtheory.

Such effects were also confirmed by Baets (1962). He found that eventhoughdithiocarbamates suchaszinebandmanebhadpositiveeffectsonyields of tobacco, they lowered the levels of proteins. It is logical to ask,therefore, to what extent such biochemical effectsmight be linked to thedevelopmentofcertainparasitic infectionsof tobacco, thathavealsobeenrecurringincertainyears.

Thorn and Ludwig (1962), likewise, have assessed the repercussionsof dithiocarbamates onhost plants.They found that, in comparisonwithcontrols,treatedbeetrootleavesshowedsignificantincreasesinglutamine,valineandleucine,alongwiththepresenceoftyrosine,whichdidnotexistinthecontrolplants.Inshort,weseehereaninhibitionofproteinsynthesis,whichistheoverallprocessthatexplainshowcarbamatesanddithiocarba-matesincreasethesusceptibilityofplants.

VII. The effects of other pesticides: new fungicides and herbicides

Wewill look ingreaterdetail at these repercussions,whichhave justasmuchimportanceforthehostplant,whenwestudytheparticulartypesofcultivation,suchasfruitarboricultureandcerealcrop-growing.

Theseeffectsappeartobenolessdrasticthanthoseofthechemicalswehavesofarstudied.Totakeonlythecaseofherbicides,itisperfectlyclearthat‘Selectivityisfarfromperfect.’Collectif(1979)hasmadethesamepoint:‘Onthewhole,onecansaythatallherbicidesaretoxicforallplants.’

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Suchtoxicitygenerallymanifestsitselfbyaninhibitionofproteinsynthesisleading to susceptibility to various attacks of parasites. This is the logicalconclusionofourexaminationoftheeffectsofthevariouspesticidesstudiedinthepresentchapter,whoseresultsweshallnowsummarise.

VIII. Conclusions

Aswecansee,theconclusionswehavedrawnfromthepresentchapterreinforcethoseofthepreviousones.Theseare:

1) Confirmation of the nature of the relations, nutritional in kind,betweenplantsandtheirparasites.

2) Confirmation that maximum protein synthesis correlates withmaximumresistance,andthataplant’ssusceptibilityislinkedwithaphysiologicalstateinwhichproteinbreakdownpredominates.

3) Confirmationoftheconceptofa‘parasiticcomplex’thatleads,inaplantwith inhibitedproteinsynthesis, toanoutbreakofparasitismthatmayeventuallybecome‘multiple.’

4) Impactsofhormonalsubstances,aswellasofvariouspesticides,onthe plant’s condition and resistance confirm the great importanceof theplant’s nutrition, especially thebalanceof the variousmajorelementsandtraceelements.

5) These results show the relation between the physiological condi-tioningof theplantbypesticides and its susceptibility toparasites.Theyclearlyshowtheconfusionthatcanbemadebetweenparasiteproliferation,duetopositiveeffectsontheparasite’sbioticpotential,andthesupposed‘resistance’ofthepathogenicagenttothepesticide.Thisconfusionoccursaboveall,ifthesupposed‘resistance’manifestsitself only under field conditions. In reality, what we then observeis only the phenomenon of inefficacy. We will return later to thisextremelyimportantpoint.

6) Theseimpactsofdifferentpesticides,whichbynowarewellattested,inevitablyraisenewquestions.Forexample:

• thedelayedeffectsofpesticides:itappearsthatthesesideeffectsareonlynoticedattheendofacertainperiod.Thismakesitdifficulttoassesstherelationship:pesticideseffectsontheplant’sphysi-ologysusceptibilitytoparasiteattack.

•


• inthesamecategory,theprobableexistenceofcumulativeeffectsofpesticides,especiallyinperennialplantssuchasfruittreesandgrapevines.Thiscouldexplaintheapparent‘suddenness’ofcertainoutbreaksofdiseaseorinsectpests.

7) Tosumup,theresultsobtainedinthischapterleadtothefollowing,almost self-evident conclusion: ‘The toxic effects of a pesticide on the parasite whose destruction is sought will also affect the host plant, making it more rather than less susceptible.’

Theseare thedifficulties encounteredwhen the soleperspectiveofpestcontrolisachemicalwartodestroytheparasite-thatistosay,thechemicalwarascurrentlypracticed.

Notes

1 Theplantshavebeenpreviouslyplacedintherefrigerator.

2 ItshouldbenotedthatalthoughDDTandotherchlorine-basedinsecticidesarebannedinFrancebecauseoftheirpersistenceinthefoodchain,numerouschemicalfungicidescontainchlorine.Ithasbeenshownthatchlorinereducesthesynthesisofaminoacidsandpromotesthedecompositionofproteins.

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61 The Failure of Chemical Pesticides in Arboriculture and Viticulture: Bacterial

Disease and Plant Physiology

PART TWO

Deficiencies and Parasitic Disease

Behind the appearance of epidemics, which intervene like additionalagentsofdestruction,liehiddendeficiencies.Suchdeficienciesalsocreateindividuals less resistant toparasites,predators, climaticvariations, andthepressuresofmigration.

MauriceRoseandP.Jored’Arces(Évolution et Nutrition,Paris,1957)

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Chapter 4

The Failures of Chemical Pesticides in Arboriculture and Viticulture:

Bacterial Disease and Plant Physiology

I. Similarity of phytosanitary problems in arboriculture and viticulture

Fromthispointonweshalllook(fromaratherdifferentperspective)attherepeatedfailureofchemicalpesticidestoprotectfruittreesandgrapevines.

Withanunderstandingoftheprovenimpactofpesticidesonthephysi-ologyandresistanceofplants,andthenutritionalrelationshipbetweentheplantandtheparasite,wecanseethatafailureofonepesticideoranotherindicatesmorethanjustineffectiveness.Italsoinvolvesnutritionalstimula-tionofthevirulenceoftheparasitethroughmodifyingthebiochemistryofthehostplant.Thisisnotso-called‘resistance’tothespecificpesticide.

This phenomenon has been demonstrated in the case of the spidermite.However,asweshall see, thesameholds true foraphids.Pearphyl-loxera,which thrives after treatments based on various pesticides such asdemeton-methyl, azinphos-methyl, vamidothion, and omethoate, offers aparticularlysignificantdemonstrationofthis.Thecaseofthepsyllids(leafsuckers)probablyarisesfromsimilarfactors.

Weshouldalsonotethedifficultyofcontrollingtheseinfectionsif,whileweseektodestroythevectors,theaphicidescausethemtomultiply.Wewillseethisdemonstratedlater,inaspecialchapteronthecontrolofviraldiseases.Inshort,wemustavoidaggravatingthe ‘parasiticcomplex’–(plant,virus,andvector)throughchemicalinterventionthathasanegativeinfluenceonthephysiologyoftheplant.

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The term ‘parasitic complexes’ signifies the simultaneous existence onthe plant of several different parasites that can combine against it. Theseincludebothplantandanimalpathogenicagents:bacterial,fungal,orviraldiseasesandinsectpests.Oneexample,justdescribed,isthecoexistenceofviraldiseasesandvectoraphids.Othersthatwewilldiscussinthefollowingchapter,involveviraldiseases,cryptogamicdiseases,andinsectpests.

These ‘parasiticcomplexes’ compelus toquestion their commoncauseandeventheveryconceptof‘disease.’Wewillbebetterabletoaddressthisissuewhenwehaveaccumulatedandexaminedtheexperimentaldataandhavediscussedthevalidityofthevarioushypotheses.

II. The exacerbation of parasite activity: ‘resistance’ or multiplication?

The exacerbation of virulence is similar in grapevines and fruit trees,attacked by the same parasites. Similar problems are encountered withincreasesofOidium, Botrytis, andproliferationof spidermites.There areincreases, likewise, inthe ‘resistance’ofaphidstopesticides.Bacterialandviraldiseasesarecontinuallyincreasingand,accordingtosomeresearchers,willbecomethe‘diseasesofthefuture.’

Wehope to show that thesedevelopmentsarise fromacommoncause,namely the modification of the susceptibility of the plant in response tochemicalproducts.

With regard to grapevines, the incidence of pesticide failure, usuallyreferredtobypathologistsas‘resistance,’iscommontoanumberofinfec-tionsincludingOidiumandBotrytisandmildew:theyhaveallincreasedincertainregions.Thisprocess,familiarfromotherdiseases,hasbeencalledthe‘boomerangeffect’.

Inthecontextof ‘parasiticcomplexes,’acariosis,black-rot,Brenner(firedisease)andbacterialnecrosishaveincreasedinvirulenceandanewdisease,eutypiosishasappeared.

Ifthesewereallcasesof‘resistance’,wewouldobservethesephenomenaof ‘resistance’ in abandoned grapevines which had not been treated withthespecificchemical.Moreover,‘ineffectiveness’isfoundintheabsenceoftreatment formore thanthreeyears.Finally, ‘resistance’manifests itself insomeareasbeforepesticideshavebeenapplied.



Certainobservers,havethereforehypothesisedforexamplethatresistantroot-stockmayalreadyexistandmayhavebeentransferredfromonefieldtoanotherandalsofromoneregiontoanother!

We think itmore likely, that thepesticideorpesticides,byaffecting thephysiologyoftheplant,sensitiseitnutritionallytotheparasite,whichthenbecomesvirulent.WehaveclearlydemonstratedthisforOidium,Botrytis,andspidermites.

This pseudo-resistance occurs with ‘fungicidal’ chemicals that inhibitprotein synthesis.Theyhave just asmuch impacton thehostplant asonthepathogenic fungus.Wewill return to thispoint later in the contextofcontrollingfruitscab.

Thismodificationofthe‘site’oftheactioninresistantroot-stocksconsistsinadisruptionoftheplant’smetabolism,thatmakesitmoresusceptibletoattack.

Thiswouldalsoexplainwhytheeffectsoftreatmentsbecomemuchmoreharmfulwhentheyarerepeated,sincetheireffectsaccumulateinthecourseofapplicationsfromoneyeartothenext.

Of course, the harmful effects of synthetic pesticides combine with anumberoffactors,outlinedinthefirstchapter.

III. Bacterial disease and the physiology of the plant

a) The repercussions of pesticide treatment in relation to bacterial diseases. The influence of disturbing changes in the nature of phytosanitary chemicals.

Morethantwentyyearsago,aspecialistonbacterialdiseasescouldalreadydrawtheconclusion:‘Currentconditionsofarboriculturehaveofferedbacte-rialdiseasesacombinationofcircumstancesthatencouragetheirdevelop-ment’(Ride,1962).

What are these conditions? The author refers specifically to so-called‘intensive’arboriculture.Headds:

‘The abandonment of copper in certain operations over the course ofthelastdecadeinfavourofvarioussyntheticchemicalshasledtorenewedoutbreaksofPseudomonas syringae.(Ride,1962).

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He adds: ‘Several aspects of the bacterial diseaseP. syringae have beenconfusedwithdamagecausedbyfungiorwithdisordersbroughtaboutbydeficiencydiseases.’

Theauthorthusdrawsaconnectionbetweensymptomsofdeficiencyandthoseofbacterialdiseases.Wewillencounterthesameobservationinrelationtootherdiseases,bothviralandfungal.Toquotethesameauthoragain:‘Bac-terialdiseasesoccurmostoften inorchardswhere copper saltshavebeenentirelyreplacedbychemicalorgano-fungicides.’Andfinally:‘Onlycoppersalts (and, in theparticular caseof infectionbyXanthomonas pruni, zincsulphate)stillcommandrespectincontrollingbacterialdisease.’

Thissumsup,inageneralway,thecausesofthegrowthofdisease,asaresultofchangesinchemicalpesticides.

Whatisinvolvedhereisanindirectprocess,nutritionalinnature,bywhichvarious chemical pesticides cause proliferation of spidermites. The samethinghappenswithaphids.Moreover,variousdithiocarbamatesdrasticallyaggravate thedevelopmentofOidiumongrapevines, in comparisonwithcupricproductsandevenpurewater(Chaboussouetal.,1968)

Similar harmful effects of chemical pesticides were also recorded withbacterialdiseases.AsDavetpointedout:

‘Thebiologicalimbalancecanspreadjustaseasilytobacteria.DeepandYoung (1965) note a recurrence of crown gall (Agrobacterium tumefa-ciens) in cherry trees treatedwith captananddichlone toprotect themagainstChaloropsisandThislaviopeis.Theybelievethiseffectshouldbeattributedtothesuppressionoffungithatwereantagonistsofthebacteria’(Davet,1981).

Wemust therefore consider thepossibility that,with the appearanceofchemicalpesticides, twoprocesseshaveplayed a role leading to the sameresult-increasingsusceptibilityoffruittreestodisease.Theseprocessesare:

• theabandoningofuseofmineralssuchascopper,whoseactiononthemetabolismoftheplantcouldbebeneficial;

• repeateduseofsyntheticpesticides,whichhaveharmfuleffectsonthephysiologyoftheplant(becauseproteinsynthesisisdisrupted).



If these effects are cumulative, and if such effects accumulate year afteryearinperennialplants,thiswouldexplaintheirincreasedsusceptibilitytodisease,aswellastheapparentlysuddenonsetofdisease.

Weshallnowturnourattentiontoanexaminationoftheeffectsofgrowthhormonesinrelationtodevelopmentof ‘fireblight.’Thisexamplelikewiseseems to confirm that it is above all the physiological state of the plant,broughtaboutby the indirectand insidious influenceofpesticides,whichpromotesthedevelopmentofthedisease.

b) The effects of growth substances and new farming techniques

Inregardtofireblightinpeartrees,researchershavenoted:‘Thegrowthhormonesused,especiallytosettheflowers,haveincreasedthetendencytoasecondfloweringperiod.Thistechniqueshouldbeeitherbettercontrolledorabandoned’.1

Thisconfirmsthatinfectionofthepeartreebybacteriaarisesprimarilythroughtheflowersandonlysecondarilythroughthegreenshoots.Thatistosay,itattacksthosepartsoftheplantwherebreakdownofproteinpredom-inates.Suchaconditioncouldbeaggravatedbycertainchemicalpesticidesandparticularlybygrowthhormones,asweshallnowsee.

Letus look, for example, at the repercussionsof 2,4-Dasdescribedbysomephysiologists.Theywrite:

‘As an example, we shall take treatment by the well-known syntheticphytohormone, 2,4-D (2.4 dichlorophenoxyacetic acid). A fewminutesafter application, the cells of the leaf stalks touched by the substancegrow longer, triggeringavisible change in thepositionof the leaves. Inhotweatherblightmayappear,notspecifically throughtheeffectof thephytohormone. After a few hours the 2,4-D has spread throughout thewholeplant,andstimulationof ‘growth,’ togetherwithdeformities,willbecomeevidentoverthesucceedingdays.Proliferationofcellstakesplaceinthedifferenttissues-inthecambium,thecortex,andthephloem-inamannersimilartothecallusesthatdevelopatthebaseofcuttings.Theseproliferationsresultincompressionofthesoftesttissuesandobliterationofthewoodyvesselsandriddledxylemvessels.Deathoccursatthisstage,accompaniedbybacterialorfungalinvasionswhichdestroythesofttissues,thatarerichinnutritionalsubstances’(Collectif,1979).

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Such is the picture of the herbicidal effect of a growth hormone.Notethe nutritional nature of the relation between development of bacteria orpathogenicfungiandthebiochemicalconditionoftheplant,followingthephysiologicaldisruptionscausedbythehormone.Ofcourseherethedeathoftheweedisintentional.However,similarthoughlessdrasticrepercussionsoccuron thecrop itself.Thismeans that2,4-D(‘agoodexample,’ say thesameauthors,‘ofthecomplexactionwhichwestillonlypartiallyunderstand,inspiteofmanydecadesofwork’)cancausedisordersincultivatedplants,particularly if it has been applied in a carefully consideredmanner, as intreatmentsoffruittrees.Thisiswhyitwouldnotbesurprisingif(througha nutritional effect, arising from an inhibition of protein synthesis) thehormonescould in thiswaypromote theproliferationofparasitessuchasbacteriainthecaseweareconsidering.

Wecouldevensaythatgrowthhormonesactinthiscaseas‘indicators’or‘demonstrators’oftheimportanceofthephysiologicalstateoftheplantinrelationtoitsresistancetovariousparasites,bothplantandanimal.

As we have seen, disruption of the physiology of the plant, especiallyof fruit treesorgrapevines, canbe causedbothbygrowthhormonesandnumerouspesticides,especiallychemicalones.

ItisundoubtedlynoaccidentthatCollectif(1979)couldmakethefollowingobservation: ‘As a consequence, perhaps, of overly intensive agriculture,bacterialdiseasesareparticularlydifficulttocontrol’.

Webelieveitisessentialtoconsidertwobasicintensivefarmingprocedures:

(1)theuseofnewchemicalpesticides(withmoreappearingeveryyear),ofteninmultipleapplications,withoutaseriousexaminationoftheireffectsonthephysiologyandresistanceoftheplantthatthechemicalsaredesignedtoprotect.

(2)excessiveuseofchemicalfertilisers,mostespeciallynitratefertilisers.We know that they generally have the effect of enriching the tissueswithsolublenitrogen,whichmakes theplant susceptible tobacteria,aswellasotherdiseases.Wewillnowsee this confirmedbyadetailed studyof thisprocess.



IV. The mechanism of effects of different environmental factors on the development of bacterial diseases. Importance

of levels of soluble nitrogen in tissues

a) The role of nitrogen in proliferation of bacteria

McNewandSpencer (1939), experimentingonsweetcorncultivated innutrientsolution,haveshownthatnitrogenprovidedtoyoungplantsistakeninto thexylemvesselsby thebacteriumPseudomonasstewarti.Therefore,it is thequantityofnitrogen in the sap thatdetermines its suitability as agrowthmedium.

Thesameauthorshavealsoshownthegreatimportanceofnitrogennutri-tionforthevirulenceofdifferentbacterialstrains.Ifsomeoftheseturnouttobelessvirulent,thisisduetotheirinabilitytomakeuseofinorganicnitrogen.Inotherwords, the virulenceof a strainofP. stewarti is closely linked toits ability to assimilate inorganic nitrogen. ‘This bacterium,’ the authorsconclude,‘dependsoninorganicnitrogenforitsexistenceasaparasite.’

Inaddition,McNewandSpencer(op. cit.)referredtoNightingale’sstate-ment:‘TheinvasionofthecorticaltissuesinappleshootsbyErwiniaamylo-vora-thefireblightbacterium–iscorrelatedwiththequantityoforganicnitrogen present. This organic nitrogen,moreover,may be related to thequantityofinorganicnitrogenfurnishedtothetreeintheformoffertilisers’

Similarly,GalleryandWalker(1940)experimentedonthetomatobacteriaPseudomonas solanacearum, which grows in the xylem. Cultivating thebacteria in anutrient solution, they showed thatwhile thebacteria growsmorequickly inanenvironmentcontaining2%dextrose rather thanonly1%,theymultiplyevenmorerapidlyinasolutioncontainingpeptonethaninanenvironmentdevoidoforganicnitrogen.

Finally,wealsolookattwoseriesofstudiesoftheresistanceofcottontoproliferationofXanthomonasmalvacearum.Thesestudieshaveshownthegreatimportanceofthenutritionofthehostplantforthevirulenceofthebacteria.

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Throughastudyoftheeffectsof28compoundswhichreactedpositivelytoninhydrin(theNHPC’s),Lipke(1968)showedthatanaline,amino-bu-tyricacid,andpotassiumwereassociatedwiththedegreeofseverityofthebacteria.Potassiumprobablyintervenesbecauseofitswell-knowninfluenceon the protein synthesis process. A deficiency of potassium results in anincreaseof solublenitrogen compounds, providing anutritional substratethatallowsthebacteriatomultiply.Inotherwords,thecottonissensitisedbecauseitstissuesarepredominantlyinastateofproteolysis.Thisfactagreeswellwiththeprocesspostulatedbythetheoryoftrophobiosis.

Similarly,workingonthesameissueinregardtovarioustypesofcotton,VernaandSingh(1974)concluded: ‘Thesusceptibilityofacottoncultivardependson severalnutritional factors.While theredoesnot seem tobeadirectcorrelationbetweenthesugarcontentandthedegreeofsusceptibilityofthecultivar,itseemsquitelikelythatthesourcesofnitrogenwouldbethelimitingfactor,playingagreaterrolethanthesourcesofcarbonincontrollingthegrowthofthepathogen.’

It is also interesting to note that while alanine and glutamic acid areshownbyotherauthors tobeessential for thenutritionof X.vesicatoria,theirutilisationbythebacteriacouldbehinderedincertaincases,andthepathogencandieofstarvationinresistantcultivars.Thisoccursasaresultofthepresenceofcertainaminoacidssuchasserine.Thisaminoacidisinfactknown tohinder thegrowthofX.malvacearum, since itopposes theutilisationofglutamicacidbythebacteria.Inthiscasetoo,whatwefindisresistancebytheplanttotheparasite,duetonutritionaldeficiency.

b) The role of the balance of cationic elements in the nutrient solution

Aswesawinthecourseofthesecondchapter,whiletheroleofpotassiumisimportant,it isquiteclearthatitactsonthemetabolismoftheplantinbalancewiththeotherelements,especiallycalcium.WerecallthatthebalancebetweenproteinsynthesisandproteolysisdependsparticularlyontheK/Caratio.Thisisconfirmedbytherelationshipbetweenbacteriaandtheplant.

ExperimentingwithbeanplantsinfectedwithErwiniacarotovora,Tejerinaetal.(1978)cultivatedbeansinvariousnutrientsolutions.



Theykeptthenitrogencontentidentical,butvariedthebalancebetweenK,Ca,andMg.Theywereabletodemonstrateaninteractionofeffectsbetweenthehostplantandthepathogen.CertaincombinationsofN,K,Ca,andMgwereabletorenderthebeancompletelyresistanttothebacteria.

Aboveall,asthesameauthorsstressed,‘Theabsenceofbacterialgrowthwhen plants were treated with 1.5% Camight be due to changes in thesubstrate,leadingtoasystematicimbalanceofenzymeactivity.’

Theyalsoadded:‘AhighlevelofCaisabletocounterbalancetheeffectofnitrogen,sincetreatmentwith2%N,1%K,1.5%Caand1%Mgdoesnotleadtovirulenceininoculatedbeanswhicharegrowingnormally.’

Thus,asForsterandEchaldi(1975)haveshownintheirexperimentsontheresistanceoftomatoestoCorynebacteriummichiganense,asupplementofCainthenutrientsolutioninfluencesthecontentofothercationsaswellasofcalciumitself.MoreoverthisisthereasonwhytheratioCa+Mg/K+Nabetterexpressesthenegativecorrelationofthelevelofdiseaseintheplants,takenindividually,thandoesthecalciumcontentalone.Asaroughapprox-imation,one coulduse the inverse ratioK/Na,whichwehavepreviouslymentioned.Thisisoftentakenbyphysiologistsasthemetaboliccriteriontocharacterisethecationicbalanceofplanttissues(CraneandStewart,1962)(Fig.1).

c) The role of the photoperiod

Aswesawabove,theeffectsofthephotoperiodsuperimposethemselvesupontheeffectsofthebalanceofcationicelements.Bothoftheseinfluencethephysiologyandthereforetheresistanceoftheplant.Aswelikewiseshowedinthecourseofthesecondchapter,bacterialdiseasesarenoexceptiontothisrule.Concerningbacterialdiseases,GalleryandWalker(1950)notethat:

• onlongdayssugarsandstarchincrease,asdoesinsolublenitrogen(inotherwords,ametabolismwhereproteinsynthesispredominates)

• onshortdaysthereisadecreaseincarbohydratecontentandanaccu-mulationofsolublenitrogen(inotherwords,astatewhereproteolysispredominatesoverproteinsynthesis).

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Thesevariationsinthevirulenceofbacteriaaccordingtothetimeofyearare explained perfectly by Gallery andWalker (op. cit.) in the followingway:‘Onshortdaystheplantscontainbothsolublenitrogenandcarbohy-drates,whichareavailable to thepathogen.Theplantsarecomparable toanenvironmentcomposedofminerals,dextrose,andpeptone.’Theyadd:‘This iswhyon shortdayswecanexpectan increase in thedevelopmentof thedisease.’ (We recall thatwhat is involved is the bacterial disease oftomatoesbroughtaboutbyPseudomonassolanacearumproliferatinginthexylem.)

d) The influence of the nature of the stock

Thefactthatthestockexertsaclearinfluenceonthesusceptibilityofthegrafttobacterialdiseasesunderlinesthegreatimportanceoftheplant’sphys-iologytoitssusceptibility-orifyouprefer,itsresistance-tothesediseases.Ride(1973), for instance,notes thatBartlett stock is ‘sensitive,’whileOldHomeismoderately‘resistant.’

However,weshouldpointoutthatsuchawayofspeakingcouldleadtoconfusion.Ifinfactastockisreputedtobe‘sensitive,’thismeansinrealitythat itmakes thegraft susceptible to thedisease.Theopposite is thecasewhenitconfers‘resistance’onthegraft.

Thisis,moreover,ageneralphenomenon,onethatweshallstudyinthechapter on the influenceof the stockon the graft’s resistance.This sensi-tisingofthepeartreeto ‘fireblight’byBartlettstockisreminiscentofthe‘sensitising’effectofBramptonstockonapricottreesandcertainvarietiesofplumtowardtheviraldiseaseSharka.Inthiscasetootheparasite’snutritiondetermines itsproliferation.Asweshallsee in thecourseof the followingchapter,thisconfirmstheoverallimportanceofthenutritionalrelationshipbetweenplantandparasite,regardlessofthetypeofparasiteinvolved.

Onthesamesubjectofbacterialdiseases,DuquesneandGall(1975)write:

‘Considering recent publications on the relation betweennutrition andsusceptibility of trees to bacterial diseases (studies by the American, H.English), it ismorereasonable to suppose that the stockaffects thenutri-tionofthegraftbycausingittobemoresusceptiblewhenthenutritionisdefective.’



According toourconceptof trophobiosis, theonlycauseof suchdefec-tivenutritionisadeficiencyinproteinsynthesis.Proteinsynthesisinturn,aswehave justnoted, is linked to thebalanceof cationic elements in thetissues.Specificallywiththepeartree,Blanc-AicardandBrossier(1962)haveshownthatthisbalanceinthegraft,particularlytheratioofdivalentionstomonovalentions, isdeterminedbythenatureofthestock.Suchabalancecouldalsoserveinthiscaseasacriterionforthemetabolismofthegraft.Itcorrespondsaboveallwiththelevelofsolublenitrogen,whichconfirmsthegreatimportanceofnitrogenforsusceptibilityofplantstodisease.

ThePasse-Crassanevariety isnotoriously sensitive toblight.Might thisnotbeduetothefactthat,apartfromapossibleintrinsicsusceptibilityofthevariety,itisusuallygraftedontoCognassier,aweakeningstock?

Toconclude:bacterialdiseasesarenoexceptiontotherulethatsuscep-tibility is linked toametabolismwhereproteolysispredominates,offeringanabundanceofsolublenutritionalsubstances,especiallysolublenitrogen.Howthencanweexplaintheparticularlyharmfuleffectsofchemicalpesti-cides?Thisistheissuewewillnowaddress.

V. Control of bacterial diseases involves taking into account the nutritional relationships between bacteria and the host

plant. Development of bacterial diseases and the nature of the relations between plant and bacteria

Wehaveshownthatbacterialdiseasealsodemonstratesthatsusceptibilityis linked to an excessofproteolysis,where soluble substances accumulatethatpromotethenutritionofbacteria.Tejerinetal.(1978)alreadyarrivedatsuchatheoryinthelightoftheirstudiesofbacterialdiseaseincarrots.Astheseauthorsthemselvesnoted:

‘Notonlygeneticfactorsbutalsoecologicalfactorsarecapableofcontrollingthepathogenesisofmicroorganisms.Inthisway,somefertilisersappliedtothesoilcaninfluencetheestablishmentofmicroorganismsintheirhost,becauseofphysiological and anatomical changesproduced in theplanttissues.

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Thevalueforthebacteriaofthesenutritionalelementsproceedingfromthetissuescouldbeanimportantparametercontrollinghowtheydevelopandbecomeestablishedintheplant,sincetherelationsbetweenpathogenandhostplantarecharacterisedbyanexchangeofchemicalsubstances.’

We now intend to study the extent to which treatments with chemicalpesticidesareresponsiblefortheexacerbationofsusceptibilitytobacterialdiseases.

VI. The effects of chemical pesticides in the plant-parasite relationship

a) Effects of cupric chemicals: the copper-nitrogen balance

Webeginbylookingatthecaseofcopper,whichstandsoutinacertainfashionbyitsclearbutstillmysteriousactiononbacterialdiseases.

Demolon (1946), in discussing the progress made in control of fungaldisordersbytheuseofBordeauxMixture,stated:

‘Ifprogresshasbeenmade(againstmildew)inregardtothetimingandmeansofapplication, this isstillnotenoughtoexplainthespecificrolethat copper seems toplay.Once researchhas explained themechanismofthebehaviourofcopper,thismightopennewpathsthatcouldtakeusfurtherandimproveasituationwhich,howeversatisfactoryitmaybe,issocostlyforviticulture.’(Demolon,1946).

In regard to the process of the anticryptogamic action of copper orBordeauxmixture,canweclaimthatwearemuchfurtheralongtodaythanforty years ago? How can we explain, for example, the fact that copperproducts,althoughineffectiveagainstbacteria,displayafarfromnegligible‘prolongedpositiveeffect’againstbacterialdiseases?(FromanINVUFLECbrochureonwitheringofthepeachtree.)

Ifcopperseemstolacktoxicitytothebacteria,isitperhapsfunctioninginanotherway?Logically,therecanonlybeoneway:anindirectaction,whichcanonlyconsistofabeneficialinfluenceonthemetabolismoftheplant,bystimulatingitsresistance.



Does themicronutrient copper have the effect of causing a decrease insoluble nitrogen in the tissues? This would perhaps hold true for otherelementsfoundinBordeauxmixture,suchassulphurandcalcium.

Infact,thereisa‘delicate’equilibriumbetweenNandthemicronutrientCuwhichhasbeendemonstratedbyauthorssuchasPrimavesietal.(1972).InstudyingtheconditionsforthedevelopmentofPiriculariainrice,theseauthors found that copperdeficiency creates an excessofnitrogen,whichunleashesthedisease.TheratioN/Cuchangesfrom35.0inhealthyriceto54.7indiseasedrice,throughadeficiencyincopper.

Primavesiet al.thinkitis‘themineralimbalancewhichmakestheplantsusceptibletoattack’(op. cit.).Astheyconcludeintheiressay,‘Itisevidentthatcontaminationofseed,soilandwaterwith‘Blast’sporeshasnoeffecton the health of the plant if there is a good nutritional balance. Even insusceptiblevarietiesthediseasecannotsurvive.’Theyspecificallystate:‘Onemustneverthelessadmitthatlevelsof18ppmofMnand2ppmofcopperaresufficientinthesoilsstudied.’

Weshouldnotethat,concerningtheprocessofcontaminationandviru-lence,theinoculumisthoughttoplayasecondaryrole.Onlythephysiolog-icalconditionoftheplantprovestobeimportant.Inourviewtheeffectofcopperandmanganese(anothermicronutrient towhichwehavealluded)wouldbetostimulateproteinsynthesis.Thisispreciselywhatthesevariousanalysesseemtoconfirm.Ontheotherhand,asweshallnowsee,chemicalpesticidespresentaverydifferentpicture.

b) Effects of chemical fertilisers and fungicides: interference with micronutrients

W.E.Ripper(7thBritishWeedControlConference)hascommented:‘Aslightincreaseinnitrogencontentinplantsincreasesparasiteattacks.’

Thesameauthorhasnotedthatplantstreatedwithcarbamatesandchem-icalinsecticidesandherbicidesshowanincreaseinthelevelofnitrogenintheirtissues.

Thesameconclusionwasreachedatasymposiumonintegratedcontrolinorchards(Bologna,1972).Thereitwasclearlystated:‘Totalnitrogenlevelsincreaseafteranytreatmentwithchemicalfungicides.’

These findings seem to explain clearly why diseases, both viral andbacterial,areunleashedwheneverchemicalpesticidesinterferewithproteinsynthesis.

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However,onemayperhapsgoonestepfurther,byrecallingtheprocessesofinterferencetheyprovoke.

Ithasbeenclearlyproventhatfertilisers,aboveallchemicalnitrogenousones, such as are oftenused inhighdoses to increase yields, cause inter-ferencewith certainmicronutrients, especially copper. (This is the sourceof the hypoglycaemia and dramatic drop in fertility in animals fed oncopperdeficientfodder.)Thisseemstodemonstratetheimportanceofthecopper-nitrogenbalanceinthemetabolismoftheplant.However,coulditbethatotherbalancesalsoplayaroleandaredisruptedbychemicalfertilisersorpesticides?

One of the principal characteristics of chemical pesticides, given theirorigin, is that they all contain nitrogen, and many are also chlorinated.Chlorinecompoundsarewellknowntoreducesynthesisofproteinsandtopromotetheirdecomposition.Thiswouldseemtoexplainhowapplicationsofthesechemicalscauseincreasesinsolublenitrogenandthesusceptibilityofplantstoparasites.However,mightnottheinhibitionofproteinsynthesisresultfromthecreationofcertaindeficiencies,suchascopperorboron?

Mrs.Huguet(personalcorrespondence)wasabletoshowthatapplicationsofnitrogentothesoilinincreasingdosesleadtoadecreaseinboronintheleavesofcherrytrees(Table4).

Table 4: The relation between applications of nitrogen fertilisers to the soil and levels of boron in leaves ( of cherry trees)

Applications of N (kg/ha) Levels of boron (ppm) in cherry leaves

0100200300

24141615

Inconclusion,Mrs.Huguetwrites:‘Thedecreaseinlevelsofborongrowsmorepronouncedoverthecourseofyears,themorenitrogenisfedtothetree...Weseemtohavereachedalevelofboronwhichisnolongeroptimalforthecherrytree.However,thisdoesnotyetattainthethresholdofatruedeficiency.’



It is hardly surprising, therefore, that treatments with chemical nitratepesticides(thatis,nearlyallfungicidesandinsecticides),repeatednumeroustimeseachyear,canalsoandperhapsmoredrasticallythroughacumulativeeffect (of thekindobservedbyMrs.Huguet in fertilisers) result inborondeficienciesafterseveralyears.Thiswouldexplaintheseoutbreaksnotonlyofbacterialdiseasesbutalsoofviralones,whichcontinuetomystifyplantpathologistsandfarmers.

It is clear, then, why many observers are concerned about possible‘confusion’betweenthesymptomsofdisease,especiallybacterialandviraldisease,andthosesymptomsthatcanbecausedbydeficiencies,especiallyofmicronutrients. As an agronomist specialising inmicronutrients wrotetwentyyearsago:

‘It is not impossible that a relationship exists between deficiencies andcertaindiseases,especiallybacterialandviraldiseases.Eitherthesediseasespromote thesymptomsofdeficienciesor thesedeficienciespromote thesymptoms of disease. For example, treeswith boron or zinc deficiencycouldbemoresusceptibletoviralorbacterialdiseases’(Trocmé,1964).

Accordingtoourtrophobiosistheory,thisdeficiencyfollowsthesequence:

Deficiency inhibitionofproteinsynthesisaccumulationofsolublesubstances(especiallynitrogenous)then,throughanutritionaleffectincreaseofthebioticpotentialandproliferationofvariousparasites(notablybacteria,andalsovirusesasweshallseeinthecourseofthenextchapter).

c) How anticryptogamics and antibacterials function. New perspectives on control, by acting on the physiology of the host plant.

Wehaveintentionallybegunbyfocusingonbacterialdiseases.Wedidthispartlybecause theyarenotoriouslydifficult tocontrol,andpartlybecauseoftheexistenceofanenigma. Thisenigmaistheeffectivenessofaclassicproduct, copper (particularly in Bordeaux Mixture). Does this pesticideindeed act ‘on the surface,’ as the classic conceptionhas it?Thebacterialdiseases themselves proliferate deep within the tissues. What then is thesourceofthiseffectiveness?Thisisthequestionwehaveposed,andwhichweanswerbycitingthebeneficialactionofcopperonthemetabolismoftheplant.

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Severalfacts,moreover,wouldseemtoconfirmtheseindirecteffects.Inparticular,some ‘fungicides’knowntobeeffectivein vitro againstErwinia amylovoraturnouttobe,incontrast,whollyineffectiveagainst‘fireblight’inorchards(Ride,1973).

Such facts seem to raise a question about how anticryptogamics work.Aretheyreallycapableofactingonthesurface?Doesitevenmakesensetotrytoachievethis?Variousinvestigatorshavedoubtedthismodeofaction.Primavesi et al. (1972) emphasise the ineffectiveness of fungicides againstPiriculariainrice.Parmentier(1959),forhispart,conteststheeffectivenessoffungicidesagainstOidiumincereals.Finally,Soenen(1975),asaresultoflongyearsofexperimentsonfungicidesinfruitcultivation,emphasises:‘Themost recently developed anticryptogamics are not necessarily fungicides,yet they interfere inonewayoranotherwiththebiochemicalrelationshipbetweenthefungusanditshost.’

Likewise, we note that such conclusions seem to agreewell with thoserelatingtothemodeofactionofcertainnewfungicides.Forexample,astudyof the action of fosetyl Al (aluminium tris(ethyl phosphonate)) leads theauthortoraisequestionsaboutthereactionoftheplant.Hewrites:

‘Allthesefactsobviouslysuggestthatthereisamechanismofactionlocatedattheinterfacebetweenhostandparasite,andnotadirectaction(ofthepesticide)ontheparasitesthemselves’(Bompeix,1981).

Suchconclusions,alreadysuggestedinourpreviouswork(Chaboussou,1980),alsoagreewiththoserelatingtocontrolofbacterialdiseases,sincethebacteriacannotbereachedfromthesurfaceoftheplant.Theaimisnolongertotrytodestroytheparasite-inthiscase,bacteria-butrathertopreventit from attacking andmultiplying. If it turns out that such a treatment iseffective,thisis-aswithfosetylAl,thesubjectofspecialstudy-becauseitinvolves ‘theparticipationof themetabolismof theplant’ (Clerjeauet al.,1981).Whatwewanttoknowiswhetherthisarisesthroughapositiveeffectonproteinsynthesis,inaccordancewithourtheory.



Notonlydoallthepreviousfindingsseemtoconfirmthis,butsodosomeresultsobtainedbymeansofcertainspecialtreatments.Onesuchisprotec-tionbyinoculationwithhypo-virulentstrains.Ahletal.(1980)performeda preliminary treatment on tobacco by injecting the roots with live butincompatible saprophytic bacteria, or even dead ones.They succeeded inprotectingnotonlyagainstasecondbacterialattackbutalsoagainstpossibleinfectionwith tobaccomosaicvirus (TMV).Thisunderlines the ideaofa‘parasiticcomplex’whichweshalldiscussfurther,andwhichiscloselylinkedtothephysiologicalconditionoftheplant.

Moreover,thisshowsthatthisresistancebroughtaboutbycontaminationwithhypo-virulentstrainsisaccompaniedbythesynthesisofnewproteins.Thequantityofproteinsisproportionate,toahighdegree,toresistancetoTMV,justasitistoasecondbacterialattack.

Similarly,Staronet al.(1970)showedthattherapidrecoveryofpeppersand tobaccoaffectedbyStolbur,when treatedwith tetracyclinesand theirderivatives, isaccompaniedbyan increaseofproteins in the tissues.Suchhealingas in the foregoingcase, through stimulationofprotein synthesis,seemsclearlyconfirmedbythefactthatlevelsofproteinsindiseasedplantsdroppedbymorethan50%attheleafblades.

Finally,itisimportanttofindoutwhether,bycertainmethodsandprecau-tions, itmight be possible to stimulate protein synthesiswithout harmfuleffects,especiallyatparticularlysensitiveperiodsoftheannualcycleoftheplant.Thiswouldresultinwhatwecouldcallanutritionaltypeof‘deterrent’totheparasite.

VII. Conclusions: new prospects of control

Generally speaking, the failure of pesticides confirms once again thenutritionalrelationshipsbetweentheplantanditsparasites.Thishasbeenconfirmedbydetailedanalysisoftherelationsbetweenbacterialdiseasesandthehostplant.Thisanalysisalsoshowsthatsusceptibilitytodiseaseislinkedtoproteolysisand,inparticular,tothesolublenitrogencontentofthetissues.

Thisalsoshowsthatthegreatmajorityofchemicalpesticides,especiallywithmultipleapplications,actasinhibitorsofproteinsynthesis.Theyrendercrops susceptible to various parasites, with viruses and bacterial diseasesformingnoexceptiontotherule.

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Toanoverwhelmingdegree,chemicalpesticidesarebasedonnitrogen,fromwhich theyare synthesised.Theyarealsochlorinated.This explainswhytheyinterferewithcertainmicronutrients,suchascopperandboron.

Thisperspectiveisbasedondatafromfieldtrials:forinstance,interfer-encewithcopperbynitratefertilisers.Thereisalsothefactthat,accordingtoourtheoryoftrophobiosis,theanalogybetweensymptomsofdeficiencyandsymptomsofdisease,especiallybacterialandviraldisease,canbeexplainedsimplyascauseandeffect.

Weshallreturntothisimportantquestionabouttherelationshipbetweendiseaseanddeficiencies,particularlymicronutrientdeficiencies.Inthefirstplace,thereistheproblemofassessinghowpesticidesandespeciallyfungi-cidesactuallyfunction.Inouropinion,forexample,theeffectsofmineralproductssuchascopperorzinconbacterialdiseases,aswellascertainotherdiseases,canbeexplainedbythereactionofthehostplant.Inotherwords,thiswouldapparentlyinvolveapositiveeffectonproteinsynthesis.

This leadsus to ask towhat extent thisprocessof effectivenessmaybea general one, on the assumption that it occurs through a stimulation ofproteinsynthesis.

Inanycase,inthepresentstateofourknowledgeoftheplant-parasiteandplant-pesticiderelationships,weareabletomaketwopoints(takingaccountoftheprecedingfindings,andfromtheperspectiveofsensiblecontrol):

1)Theveryobjectivesofcontroleffortsarequestionable.Itisuselesstotry todestroybacteria through toxicprocedures.The toxicity of chemicalpesticidesaffectstheplantitself.

Such instancesof ‘poisoning’, someofwhichappear tobebenign,havethephysiological effectof inhibitingprotein synthesis.Thefirst stagemaybeinterferencewithelementssuchascopperandboron.Thefailureofthesenewchemicalfungicides(anilidsandothers)canbeexplainedbyaninitialstepinmetabolismthatrelatestodeficiencies.Thiswouldalsoexplain,atthesametime,thesimilaritybetweenthesymptomsofdeficienciesandthoseofdisease.

Thefirstmeasurethatshouldbetakenistoprohibittheuseofallchemicalpesticides(fungicides,insecticides,acaricides,andgrowthhormones)wherethepossiblyharmfuleffectsoftheirnitrogenandchlorinecontentsarenotknown.



This includes, in fact, all synthetic chemical pesticides, all the more sobecausewedonotknowthecumulativeeffectofthesepesticideswhenusedin multiple treatments throughout the season, particularly for perennialplants.

2)Ifthereisafairlydirectrelationshipbetweenthediseaseandoneortwodeficiencies,weshouldbeabletodetectpossibledeficiencies inordertocorrectthem.Thiscanbeachievedbyappropriateanalyses,carriedoutespeciallyduringsusceptibleperiodsintheannualevolutionarycycle,suchasthefloweringperiod.

On this subject, we have some reliable figures on which to base ourhypothesis.Theserelateespeciallytomicronutrientssuchasboron,whosegreatimportancewehaveseen,aboveallinitsrelationtonitrogen.Justasthedeficiencycancomefromthesoil’soriginalcomposition,itcanalsoarisefromlackofavailabilityduetothephenomenaofinterferencebynitrogenousfertilisers,orthroughadeficiencyinorganicmatter.

Apartfrommicronutrientdeficiencies,weshouldalsoconsiderthebalanceofcationicelements,whichaswehaveseenarealsoquiteimportant.OnecriterionthatseemsfundamentalistheK/Caratio.Itiswellknownthattherelationshipofcalciumtoothermicronutrientsisveryclose.Boronisknowntokeepcalciuminasolubleform,whichiseasilyassimilatedandthereforephysiologicallyactive.

Ontheotherhand,justaswithcationicelements,wecangrasptherela-tionsbetweentheelementsthemselves.AsD.Bertrandpointedout,boronisonlyactiveincombinationwithmagnesium,manganese,andmolybdenum.This appears to explain the attraction and effectiveness of the ‘micronu-trientcomplexes’advancedbysomecompaniesthatproducephytosanitaryproducts.

Ingrapevineswithaborondeficiency,forinstance,thepracticeofusingfoliarsprayswithamicronutrientbasehasled,intwoyears,toanincreaseintheratioofB/Znfrom11to47,alongwithdisappearanceofthephenomenonoffailuretosetfruit.

Moreover, it isnormal tofind (whetherwith sunflowersorwithgrape-vines)thatthebeneficialeffectsofboronbeginatthefloweringstage.Thisisinfact,aswehaveseen,thesensitiveperiodofthecyclewhereproteolysispredominates.Thisproteolysiscantoadegreebearrestedbyapplicationsofborontothetissues.2

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Inthesameway,thiscouldexplainthebeneficialeffectsofcupricspraysinlateautumnagainstvariouscryptogramicaswellasbacterialdiseases.

Finally, it seems that the results of research into correctionof deficien-cies,withtheaimofstimulatingproteinsynthesisandobtainingmaximumresistance to variousparasites, conformwith abiochemical state that alsocharacterisesvarietalresistance–inotherwords,thegeneticeffect.

Thus,inthecaseofapplescab,WilliamsandBoone(1963)recorded:‘Thevariety called Cortland, which is susceptible to all strains of Venturiainaequalis,containsasparaginelevelsof1.969(anaminoacidnecessaryforthegrowthofpathogenicfungi),whiletheresistantvariety,McIntosh,onlyhaslevelsof0.756.’Thiswouldseemtoconfirmclearlythat,inthiscasetoo,resistanceandahighlevelofproteinsynthesisgotogether.

However, we should also remember the statement: ‘The gene can onlyexpressitselfinrelationtootherfactorsintheenvironment.’Wehaveseenthisconfirmedbyclimate,stock,andthephysiologicalcycleoftheplant,aswellaswiththesoil,fertilisation(whichweshallreturntolater),andfinallytheeffectsofpesticides.Thatistosay,geneticfactorsareonlyoneelementandtheiractioncanbethwartedbyawholeseriesofothers,most impor-tantlybytheeffectsofchemicalpesticides.

It isconceivable thatsuch factors,especiallychemical treatments,couldcounteractvarietalresistance,quiteapartfromeffectsontheplant’sphysi-ology.Incontrast,controlbasedonadequate‘nutritionalconditioning’canonlybeadvantageous.Throughit,onewouldattempttorecreatea‘natural’state of physiological resistance.Results achieved in antifungal control bymeansof‘nutritionalsprays’furtherencourageustocontinuewiththislineof study for controlling bacterial and viral diseases. It becomesmore andmoreclearthatthisistheonlycourseofconductthatmakessense.

Notes1 Chaboussoudoesnotgiveasourceforthisquotation

2 F.Chaboussouunpublishedresults

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Chapter 5

Plants and Viral Diseases

I. Environmental factors and viral diseases

Likebacterialandfungaldiseases,viraldiseasesareagainontheincrease.Marrou (1970), for instance, wrote of diseases of market garden plants:‘Sincemarketgardenershavebecome familiarwith themaincryptogamicparasites andhow to control themwith effective fungicides, viraldiseaseshavetakenonamoreimportantrole.Thesediseasesarefearedbecausetheiroriginseemsmysteriousandtheirdevelopmentinsidious.’

Inthelightofeverythingsaidsofar,wemayjustifiablyhavecertainreser-vationsabouttheimpactsofthenewsyntheticfungicides.Tociteonlyoneexample,morethanten inorganicchemicalanticryptogamicshaveprovenineffective against Phytophthora cactorum in strawberries (Nourrisseau,1970).Aswehaveseenabove,thisraisesthequestionofthecausalmech-anismbehindthesefailures.Inotherwords,whataretherelationsbetweenplant,pesticide,andparasite?Attheendofthechapterweshalldealspecif-icallywiththeissueoftherelationshipbetweenplantandpesticide.Aswehaveseenabove, this isextremely important,althoughclassicalphytologyhashardlyevenlookedatit.

Furthermore,ithasalsobeenclaimedasacharacteristicofviraldiseasesthat theyaregeneralised, incurable, transmitted through thegrafting,andshowvariations in theexpressionof their symptoms.Finally, it is claimedthatplantshavenodefencemechanismagainstviraldiseases.

Wehavetriedtoshowthattheinhibitionofthepathogenicagenthasitsorigin in the plant’s deficiency in the nutritional elements needed for thepathogen’sgrowthandreproduction.Weshallnowseehow,inthecaseofviral diseases likewise, virologists dispute the presence of phenols in thetissuesasapossiblefactorin‘eliciting’thevirus.

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Weshouldalsopointout thatvariation insymptoms for thesameviraldiseaseclearlyshowsthatthephysiologicalstateoftheplant,andthereforethe nature of the environment, plays a role.With regard to the effects oftechniquesof ‘protection,’ Limasset andCairaschi (1941) could justifiablycomment:

‘Whenastrainofdiseasetriggersoffaprotectivemechanismintheplantagainstthatdisease(Tobaccoringspot)afteraclinicalcure,thisrepresentsanacquiredtoleranceoftheplanttowardthedisease.Theplantiscuredbecause itno longerreacts to the infection.It isnot thepresenceof theviruswhichconstitutesthediseasebuttheviolentreactionoftheinfectedcells.’

Symptoms are the expression of the plant’s reaction. Their variability,therefore,signifiesthataplantcaninfact‘resist’theviralinfectionpartiallyoreventotally,dependingonitsconditioningbyenvironmentalfactors.

Thisjustifiestheideathatintreatingviraldisease,‘Weactuponthehost,andnotagainstthediseaseitself.’Inthecourseofthischapterwewillseenewconfirmationsofthis,whichalsogivehighprioritytotherelationsbetweenplant and virus. Three possible outcomes have been proposed by Lepine(1973):

1)‘themostfrequentlyposedhypothesis:thealiennucleicacidimposesitsownmodeofproductiononthecellsothatthecell,fortheshorttimeitcontinuestolive,onlyproducesviralproteins.

2) ‘the cell, in refusing the alien nucleoprotein, metabolises it for theproductionof itsownnucleoproteins.Itwillsurvive,itrecovers,andthisassimilationofanexogenouselementtriggersofftheimmunityofitstissuesuponwhichtheplant’sacquiredresistanceisbased;

3)‘withoutallowingitselftobeinvadedbythevirus,yetunabletoassimi-latetheelementscompletely,thecellintegratespartofthenucleicacidofthevirusintoitsownstructures.Inthisway,theviralinfectionremainslatentandunperceived,whetherinvegetativeformorintheformofanexogenousadditiontothehereditarymaterialorprovirus.’


Theseconsiderations,applicabletovirusesinanimalsorhumans,canbeperfectlyextrapolatedtovirusesinplants.Theyunderlinethemajorimpor-tanceofthefactorsbehindtheplant’sreceptivenesstothevirus.

Inthecourseofthischapter,weshallencountertheparasiticcomplexestowhichwehavealreadyalluded:thatis,the ‘association’ofbothfungalandviraldiseaseson the sameplant.Whatdetermines the ‘sequence’ of theseinfections?Isitfirstaviraldisease,thenafungalone?Orcouldtherebeattheoutsetafactorcommontoboth?

Weshouldpointoutherethattheheadingof‘viraldiseases’nowincludesseveraldiseasesrelatedtospecificmicroorganisms.Thankstothelatestinves-tigativemethods (using scanning electronmicroscopes), researchers havebeenabletodiscovervariousorganisms,withnamessuchasmycoplasmas,spiroplasms,rickettsias,andviroids.Wenote,moreover,thattheseenormousmagnificationsalsohavesomedrawbacks.Atsuchalevelofmagnification,someresearcherscomplainofdifficultiesinidentifyingtherealorsupposedpathogenicagent.Fortheagent/diseaserelationshipstillhastobeproven.

Thisiswhatleadsustomakeacloserstudyoftheeffectsofthenutritionofplantsthroughfertilisation(thatis,thecompositionofthesoil)and,likewise,inrelationtothegeneticnatureoftheplant.

II. Inorganic fertilisation and the virulence of the virus

As Bawden andKassanis (1950) note, ‘Viruses seem to be parasites bynature. So one would conclude, therefore, that their ability to reproducemustbeaffectedbychangesproducedinthemetabolismofthehostplantcausedbyvariationsinnutrition.’

Atthetimetheywerewriting,theonlystudytheycouldrefertoaddressedthewayinwhichnitrogentendedtoaffectthevirulenceoftobaccomosaicvirus.

TheseauthorscarriedoutaseriesofexperimentsonthetobaccomosaicvirusandthepotatoXvirus,whichweshallreturntolater.Astheyconcluded,‘Theexperimentsconcerninginorganicnutritioninplantscanhardlyhopetoyieldinformationaboutthemechanismofproliferationofthevirus.’

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Instudyingtheeffectsofbothorganicandinorganicfertilisationonthevirulenceofthevirus,weshallattempttoworkoutthereproductivemecha-nism,whichtheauthorsseemtolinktoocloselytovirulence.

We shall begin by examining the effects of inorganic fertilisers: first,becausethesehavereceivedthemoststudy;second,becausetheyhavemostoftenbeenblamed formakingplants susceptible to viral diseases.This isparticularlytrueofnitrogen.

a) Repercussions of nitrogen fertilisation

Martin(1977)baseshisanalysisoftheeffectsofnitratefertilisationonanumberofdifferentworks,includingthoseofSpencer(1941-1942),BawdenandKassanis(op.cit.),Forster(1957),Cheietal.(1952)andTomaru(1967).

AsMartin(op.cit.)notes,‘Relativelylittleresearchhasbeendoneontheroleofinorganicnutritioninviraldiseases.’Hesuggeststhatthereasonforthis lies in the almost exclusively nucleoproteic nature of these parasites,whichhasledthegreatmajorityofresearcherstoexaminetherelationshipbetween the virus and competitionwith the normal proteins and nucleicacidsofthehostplant.Hestates:

‘Thebiosynthesisof the virusdependson thematerials already synthe-sisedbythehealthycell,withtheaidoftheenzymesofthehostplant.Theimportanceof the roleof themineral elements in thesehealthymecha-nismsbecamesecondaryinthestudyoftheinfectionassuch.’

Wemaynowquerywhetherthisistheproperwaytoposethequestion.Martinnotesapparent contradictions in theeffectsofnitrogen fertilisers,,pointingtothecloserelationshipwhichseemstoexistbetweennutritionandtheappearanceofsymptoms.Thus,intensiveuseofnitrogenfertilisersleadstoanincreaseinthesymptomsoftheYDonionvirus.Yettheoppositeistrueinthecaseofbeetrootyellowsvirusandinpotatoleafroll.Somevarietiesof beetrootdonotdisplay any symptoms in spiteof liberal applicationofnitrogenfertilisers,eventhough100%oftheplantsmaybeinfected.


Theseresultsgiveusanadditionalreasonforcarefullydistinguishingtheproliferationofthevirusfromthefirstevidenceofdamage,inotherwords,thesymptoms.

With nitrogen fertilisers, generally speaking, it would seem that anexcessofnitrogencouldbebeneficialforthegrowthoftheplant,butatthesametimefortheproliferationofthevirus.(Thesameholdstrueforotherdiseases.)Thesymptomsappearwhenthenutritionalcompetitionbetweenvirusandplantbecomesdetrimentaltotheplant.Thisistheperspective,itseems,fromwhichweshouldviewtheideasofCervenka(1966),asreportedbyRasocha(1973):

‘Nutrition has a considerable effect on the state of health of the plant.Nutrition,andparticularlytheratiosofN,PandK,mayaffectnotonlythesymptomsbutalsotheresistanceoftheplanttodisease,theresistancecausedbyage,andinparticularthedistributionofinfectionintheplant.’

Böning(1967)pointsoutthatisolatedandhighinputsofnitrogenfertil-iser serve toprolong thevegetative stageof thepotato,which leads to theappearanceofsymptomsofviraldisease.

Nitrogenandotherformsoffertiliserdonotaffectonlythenutritionoftheplant.Theyalsoindirectlyaffectsthecompositionandlifeofthesoil.Wearereferringheretoeffectsonmicroorganismsandtothephenomenonofinterference,particularlyregardingmicronutrients,towhichweshallreturnlateron.

b) Repercussions of phosphate fertilisers

Incontrasttonitratefertilisers,alkalinephosphatefertilisershaveabene-ficialeffectagainstviraldiseases.Bypromotingmaturity,theybringforwardthestageofresistanceintheplantbroughtaboutbyage.Thisisafactorofresistancethatwehavealreadyencounteredinfungaldiseases.Viraldiseases,therefore,comeunderthegeneralheadingoffactorsofresistance.

Thus,referringtotheresistanceofpotatoestotheXvirus,Scheperset al.(1977)notethatsupplementarydosesofphosphateshowtheoppositeeffectfromthatofnitrogen,whichmakestheplantsusceptibletothevirus.

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TheresultsofRasocha(1973)ontheresistanceofpotatoestotheYvirusseemclearlytoconfirmpreviousresults.Wethinkitworthwhiletoprovidesome details here. These studies on the effects of NPK fertilisation werecarriedoutunderglass.Theyinvolvedeightvarietiesandwerecarriedoutoverthreeyears,from1966to1969.Theirconclusionswerethefollowing:

‘Considerabledifferenceswerenoticedinthestateofhealthoftheplants,whichreceivedvariousnutritionaltreatments.Asanaveragefortheperiod1966-1969, the greatestnumberofhealthyplantswas foundamong thosereceiving the ‘nutrient free’ treatment, or the treatment with extra P2O5(Table5).

Table 5: Percentage of healthy potato plants (virus free), according to type of fertilisation

Treatment Percentage of healthy plants

Nutrient freeSurplus P205K20 deficiency K20 supplement Standard NPK sample N in excess P in excess

40.9%32.2%25.1%23.8%20.7%16.7%16.4%

Rasocha (op. cit.) also confirms that thehealthof thepotato is affectedtoaconsiderabledegreebythetimingoftheinfection.Thelaterthistakesplace,thefewerthetubersaffectedbytheYvirus.Phosphatesactinpropor-tion to thematurityof theplant,andconsequentlyat thestagewhereagerelatedresistance intervenes. It isbecauseof theplant’sbiochemical state(thebalanceofproteicnitrogenandsolublenitrogen)thatexcessivenitrogenfertilisationoraninsufficientamountofphosphatecausesmaximumlevelsofdisease.Strongandisolatedtreatmentswithnitrogenousfertilisers,whichprolong the vegetative period, retard maturity and the resistance that islinkedtotissueage.

In experiments on the potato X virus, Bawden and Kassanis (op. cit.)showedthefollowing:


• Psimultaneouslystimulatesbothplantgrowthandconcentrationofthevirus.

• Kalsoincreasesplantgrowthbut,incontrast,reducesconcentrationofthevirus.

Theseresultsagreewitheachotherasfarasthepotatoisconcerned,ifoneiscarefultodistinguishbetweentheconcentrationofthevirusandthehealthoftheplant.Itseemsthereforeclearlyestablished-andofvitalimportancetoagronomy-thatthelevelofconcentrationoftheviruscannotalwaysbeavalidcriterionofitsvirulence.

Otherstudieswerecarriedoutontobacco.BawdenandKassanis(op.cit.)havestudiedthecombinedeffectsofNPK,sincethesemajornutrientscanonlyworkinbalancewitheachother,andnotontheirown.TheseauthorsalsofoundthatPincreasesbothplantgrowthandtheconcentrationofthevirus in the sap.Furthermore,under theconditionsof theseexperiments,N only stimulates plant growthwhen P is present. Similarly,N increasesconcentrationofthevirusinthesap,butonlyinthepresenceofP.

However, they add: ‘Plant growth and the level of concentrationof thevirus are not in complete accord.While K has a positive effect on plantgrowth,ithasanegativeeffectontheconcentrationofthevirus.’Theirfinalconclusionsareasfollows:

‘Itseemsthatininoculatedleaves,aswellasinthosewhicharesystemati-callyinfected,thevirusmultipliesmorequicklyandextensivelywhenthenutritionofthehostplantisabletoproduceavigorousplantthanwhengrowthisslow.’

Thisraisesthequestionofthephysiologicaldefinitionofvigour.(Weshallreturntothislater.)

Bawden and Kassanis (op. cit.) conclude from their experiments thattheirresultsdonotseemtoconfirmthoseofSpencer(op.cit.).AccordingtoSpencer,nitrogen specifically stimulates themultiplicationof thevirus,anditseffectisindependentofplantgrowth.BawdenandKassanisadmit,moreover,thattheycannotgiveanyexplanationforthesedifferences.Theyobserve,nevertheless,thattheywereexperimentingontobacco(Nicotianaglutinosa),whileSpencerwasworkingonbeans(GoldenClustervariety).

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It ishighly likely, theyremark,thatnitrogenaffectstheinfectioninonehostplantbutnot inanother. It seemsthat themetabolismofnitrogen intobacco(Solanaceae)couldbefundamentallydifferentfromthatinalegumesuchasthebeanonwhichSpencerworked.

The latter suggests,moreover, that the process ofmultiplication of thevirusislinkedmorecloselytothesimpleformsofnitratethantothosewherenitrogenhasalreadybeensynthesisedinthenormalproteins.

Undoubtedlywewillhaveaclearerpictureaswestudytheeffectsofpotas-siummore closely.Wehave alreadypointedout someof its physiologicaleffects,aboveallinrelationtotheothermajorelements.

c) Repercussions of potassium fertilisation

Generally speaking, we can say that nitrogen, especially when appliedexcessively in fertilisation, tends tomake plantsmore susceptible to viraldiseases(justasistrueforfungalandbacterialdiseases).Ontheotherhand,wefindtheoppositeistrueforpotassiumfertilisation.

In the case of tobacco, for example, Dufrenoy (1936) notes a greatersusceptibilityinplantscultivatedinnutrientsolutionswhichwererelativelydeficientinK(Fig.3).

AccordingtoRasocha(op.cit.),whomaintainsthatnutritionofaplanthasaconsiderableeffectonitshealth,theNPKbalanceaffectsatoneandthesametime:

• thesymptomscausedbytheYvirusinpotatoes.• resistancetofungaldiseases.• thespreadofthevirusintheplant.

Looking especially at potassium, Rasocha notes that its effects varyaccordingtotheformofthepotassiumfertiliser.Ineveryway,heseespotas-siumasthemosteffectiveofalltheelementsincontrollingdisease.

Workingonbeetrootyellowsvirus,Warcholowa(1968)studiedtheeffectsofdifferentlevelsofKbothonthediseaseandonthelevelofinfectionbythevectorMyzuspersicae.InthecaseofKdeficiency,thesymptomsofthediseasebothappearearlierandaremoreserious.Theyare,accordingly,attheirweakestinplantsthathavehadthelargestdoseofpotassium.


Effectsonthebiochemicalcompositionofthetissuesareequallysignifi-cant.Whileyellowsvirusincreasesthecontentinreducingsugars,potassiumcounteractsthiseffectoftheinfection,reducingtheplant’ssugarloss,whileyieldincreasesinparalleltothelevelsofpotassiuminthenutritivesolution.

Weseeherethebeneficialeffectsofpotassiumthatstemfromitsactivityinproteinsynthesis,mediatedbyitsinfluenceonsugarandphosphatemetab-olism.Weknowtheimportantroleplayedbyphosphorusinthephenomenaofpotassiumfixation.Thisgivesitafundamentalroleinthesynthesisandstructureofproteins.

Fig 3: Percentage of tobacco affected by spotted wilt, according to the K/N ratio. (After Dufrenoy, ‘Spotted-Wilt,’ Ann. Epiphy., 1937.)

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Potassiumislinkedtothemigrationofaminoacidsfromtheplacewheretheyareformedtothesiteswheretheyareused.

Theanalysisof therepercussionsofpotassium,according to itsbalancewiththeotherelements,seemstoshowthatitsbeneficialactivityislinkedtoanelevationofthelevelofproteinsynthesisthatitisabletoproduceintheplant.

Thiscouldexplaintheapparentcontradictionsthathavearisenfromsomeexperiments. For example, when Bawden and Kassanis (op. cit.) did notobtainthesameresultswhenexperimentingontobaccoandpotatoes(twotypesofSolanaceae)asdidSpencer(op.cit.) inexperimentsonthebean,itmaybethatsomelegumeshaveacompletelydifferentmetabolismfromthatoftheSolanaceae,especiallywithrespecttonitrogen.Dufrenoy(1936)commentsthatwhileSolanaceaearesulfurplants,legumessuchasalfalfaarechlorineplants.

Nguyenetal. (1972)studiedthissubjectspecifically,workingonalfalfa.TheyalsostressedthatagoodbalanceofNPKleadsto:

• adecreaseintheaminoacidcontentofthetissues,• anaccelerationoftheirincorporationintoproteins,• anincreaseinyields.

Theseauthorsnoteinpassingtheimportanceofpotassiumforoptimumproteinsynthesis. Inalfalfa, it is the interactionofphosphorusandpotas-siumthatisespeciallymarked.Thisshowstheparticulareffectofnitrogeninlegumes.Itoftenhappensthatthesametypeoffertilisationcanhaveverydifferenteffectsonthemetabolismofplantswhicharebotanicallydistinct,andthereforeontheirresistancetodisease.

Withalfalfa,whilenitrogenfertilisersobviouslyhavelittleeffect(whichislogicalenoughbecause this legume is nitrogen-fixing),phosphoruscausesanincreaseinserineandalanineinthetissues.Theratioofthefollowingpairsofsubstancesalsoincreases:

aspartic acid + asparagine

glutamic acid + glutamine

Inthiscase,asintheothers,apotassiumdeficiencyleadstodecompositionofproteins,andthereforetoincreasedsusceptibilityoftheplanttovariousdiseases,includingviraldiseases.


Still on the subjectof the effectsofpotassium fertilisers,Russell (1972)experimentedwithtwovarietiesofbeetroot:Sharpes’Klein,sensitivetotheBYVvirus,andMarisVanguard,amoretolerantvariety.Thesetwovarietieswerecultivated,usingthesamecompost,withfiveapplicationsoffertiliser.Theresultswereasfollows(Table6):

Table 6: Harvest losses in beetroot according to the type of fertilisation

Treatment Harvest losses in the roots due to the BYV virus

Sharpes’s Klein Maris Vanguard

No fertiliser+ NaCl+ KCl+NO3Na+NO3K

39.642.735.948.055.5

27.847.136.434.128.9

Theauthorscametothefollowingconclusions:

‘InSharpes’Klein,theadditionofnitrogenintheformofsodiumnitrateor potassiumnitrate increases losses due to BYV infection.Conversely,addingnitrogendoes not affect the tolerance ofMarisVanguard to thevirus.ChlorineionsseemtolowertoleranceinMarisVanguardbutnotinSharpes’Klein.’

Thesevaryingresults raise the issueof the ‘availability’of theelements.Thisavailabilityisdeterminednotonlybytheirbalanceinthefertiliser,butalsobytheregulatorysystemsofgrowthanddevelopmentintheplantwhichgoverntheformationofproteinsandprotoplasm.Thisexplainstheimpor-tanceoftheotherfactorsofnutrition.Thesearethemicronutrients,growthsubstances,pesticides,herbicides,andfinally,organicfertilisers.

d) Repercussions of micronutirents

Regardingbacterialdiseases,wehaveseenoverthecourseofthepreviouschapterthatresearcherssometimesassociatetwodifferentthingsaspartofthesameprocess:deficienciesinmicronutrientsontheonehand,andtheactivationofviraldiseases(whetherbacterialorfungal)ontheother.Trocme(1964)posedthequestionintermsofanalternative:adeficiencyprecedingandcausingdisease,ordiseasecausingadeficiency.

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Wehaverespondedbychoosingthefirsthypothesis.Wehavebasedthischoice onour theory of trophobiosis, according towhich all deficiencies,including water deficiency, lead to a deficiency of protein synthesis. Thiscreatesanincreaseofsolublesubstancesinthetissuesandultimatelyleads,byanutritional route, toanoutbreakof thepathogenicagent.Thepoint,therefore,istoknowwhetherviraldiseasesandothermycoplasmosesobeythesamerule.

Wemustpayspecialattentiontotheconvergenceofsymptomsbetweenthoseofthedeficienciesandthoseofthediseases.Inthecaseofthegrapevine,someobserverswhohavepaidcloseattentiontothereactionsofvineyardstofertilisationwereabletoconcludeinthecourseoftheirtrials:

‘The vineyard,moreover, shows examples of numerous attacks of viraldiseases. The effects they cause (discoloration, curling, changes in leafform)havemade the symptomsof deficiencymore difficult to identify’(DelasandMolot,1967).

This is hardly surprising if the deficiencies are the origin of viral andrelateddiseases.Therearemanyauthorswhohavedrawnparallelsbetweentheexistenceofcertaindeficienciesandthetriggeringofdifferentdiseasesorevenoutbreaksofinsectpests.Asearlyas1932,Labroussenotedthatborondeficiencymadebarleymoresusceptibletoattacksofleafstripe,aswellasmildew.Expertsfrequentlynotethatbeetrootplantscansufferfromaborondeficiency,withoutrecallingthatthisdeficiencyleadstoafungalinfection,Phomabetae,1whichdisappearswhenboronisaddedtothesoil.Whatweseehereishowcorrectionofadeficiencycancureadisease.

Anotherexampleisthatofgrapelead(Stereum),whichcanalsobecuredbyapplicationsofboron(BranasandBernon,1954).

Marombadisease,occurringintheDourovalleyinPortugal,wasduetoborondeficiencyandwaseffectivelyhaltedbytheapplicationofthiselement.Itisalsointeresting,whilelookingatthegrapevine,tocomparethesymptomsofdisease-likedeficienciestothesymptomsoftherealdisease.Drawingonthecollectivework,‘Viral Diseases and Similar Afflictions of the Grapevine’,wehavedrawnupinTable7alistofthesymptomsofthedeficiencies,alongwiththediseaseswithsimilarsymptoms.


Table 7: ‘Convergence’ of the symptoms of deficiencies and those of viral diseases and other infections of the grapevine

Diseases Deficiencies Other damage Other diseases with similar symptoms

Fan leaf BoronZinc

Blossom drop and formation of seedless berries

Aucuba mosaicFlavescence doree Bois noir

Leaf roll Boron Magnesium Potassium

Mites Flavescence doree

Corky bark BoronBacterial necrosis (Bacterial blight) ExcoriosisMaladie de bois strie

Flavescence doree

Boron Pierce diseaseLeaf roll

Veinal necrosis

Boron Esca disease

However,thisismorethanjustasimpleconvergencebetweenthesymp-toms of deficiency and those of disease. A cause and effect relationshipemergesfromthisconfrontation.Wehavecitedsomeexamplesofdiseasescuredbyacorrectionofdeficienciesaboveandreturn to this in the thirdpartofthiswork.Weshallnowconcentrateontherelationshipsbetweenthemicronutrientsandviraldiseasesandanalysevariousworksonthissubject.

LockardandAsomaning(1965)studiednutritioninthecacao(TheobromacacaoL.)inrelationtothe‘swollenshootvirus.’Theyobservedthatcertainswellings in theshootsresembledtheblisteringcausedby thevirus foundinplantswithcopperdeficiencies.Fromthistheyconcludedthatthereisapossibleinteractionincacaobetweennutritionandvirus.

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Applicationsofiron,zinc,oracombinationofiron,zinc,andmanganesewere shown to correct the symptoms causedby certain viruses.However,theresearchersnoticedthatcopperisrequiredforproliferationofthevirus.Theremay thereforebenutritionalcompetition forsomeof themetabolicproductsofthecacaoplantbetweenthe‘swollenshoot’virusandtheplant,resultinginsymptomsofcopperdeficiency.

LockardandAsomaning(op.cit.)carriedouttwotypesofexperiments,onebasedon theeffectsofdeficienciesorexcessesofmajorelements, theotherinvolvingmicro-elements.Eachtreatmentwasappliedbothtohealthyplantsandtoplantsinfectedwiththespecificvirus.

Aftertwomonthsofcultivation,plantsdeficientinboron,zinc,andironwereonthepointofdisappearing.Sincetheexperimentwastherebyinvali-dated,theexperimentershadtoaddasmallquantityofmicronutrientstothenutrientsolution.

Inthecourseoftheseexperiments,theauthorswerealsoabletoobserveaworseningofthesymptomsofthevirusthroughalackoflight.Adrasticreductioningrowthaccompaniedthesesymptoms.

Intheseexperimentswithmicronutrients,theeffectofthevirusisstrongestintheleaves.ThereisadecreaseinlevelsofFe,Mn,Zn,B,Mo,andNa,andanincreaseinAl.Intheroots,thevirusleadstoareductioninlevelsofFe,Al,andNaandanincreaseinthelevelofMn.

These effects interfere with so-called ‘nutritional’ treatments that aresuperimposedonthoseofthemicronutrients.Thisverifiessomeoftheinter-ferencewithlevelsofnitrogeninthestemsandwithPandMnintheleavesandstalks.

ThestudiesbyRussell(op.cit.),ofwhichwehavealreadyspoken,werecarriedoutonviraldiseasesofbeetroot.Theyarealsorelatedtofertilisationandthebehaviorofaphidvectors,towhichweshallreturn.Russellnotes:

‘Themanifestationofresistancetoaphidsandtoinoculationwithvirusinsugarbeetcouldbealteredbyvariousfactors.Theseincludetheconcentra-tionsofmajorelementsormicronutrientsinthesoil,alongwiththefactorsthataffecttheconcentrationsofsugarsandaminoacidsintheleaves.’


Underglass,saysRussell, ‘theabsorptionofcertainnutritionalelementsby the rootsof the sugarbeet couldprofoundly alter themanifestationofresistancetoaphidsandtoinoculationwiththevirus.’Thesituationisthesamewithcertainmicronutrients:

• for example, while applications of Li, Zn, or Ni salts prompt theappearanceofaphidsontheleaves,boronactuallydiscouragesthis;

• reproductionofaphidsisacceleratedbyNiandSnsalts;• the transmissionofBYV (beet yellows virus) is increasedbyLi and

boron,andreducedbyCu,Zn,andtin.

Yetmicronutrientswhichseemtoencouragetheestablishmentofaphidsdonotalwayspromotetransmissionofthevirus.Plantswhichhavereceivedtreatments of cobalt nitrate are found, 48 hours after infestation, to havesignificantlymoreaphidsperplantthanthosetreatedwithiron.However,fewerplantstreatedwithcobaltbecomeinfectedwiththevirus.

Such results, the author observes, clearly confirm that resistance to theestablishmentof aphidsand resistance to inoculationby thevirusarenotnecessarily related. He adds:‘The concentrations ofmicronutrients in theleavesmayaffecttheestablishmentbothdirectly,byalteringthecompositionofthediet,andindirectly,bychangingthemetabolismoftheplant.’Weseescantdifferencebetweenthesetwosuggestions,whichbothrelatetoamodi-ficationofthephysiologyoftheplantthroughtheactionofmicronutrients.

Russell(op.cit.)notesinpassingafactwellknowntoagronomists,thattheconcentrationofthemicronutrientsinthesoilvariesenormouslyfromplacetoplace.Inthefield,therefore,thisleadstoimportantvariationsinresistancetothevirus.Weshallreturntotheseproblemsinthechapteroncontrollingviraldiseasesincereals.

Russell’swork,togetherwiththatofLockardandAsomaning,showsthegreatimportance,forresistancetoviraldiseaseandtootherdiseases,ofthemicronutrients’ effects on the physiology of the host plant. These studiesentirelyconfirmourpositionontherelationshipbetweenplantandparasite.Thisisprimarilynutritionalinnature,anddietarydeficienciesconstituteafundamentalfactorinthesusceptibilityofplantstoviralandotherdiseases.

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Inthecourseofthepreviouschapter,wehaveseenthatpesticidesusedtotreat fruit trees,orchemicalnitrogen fertilisers incorporated into thesoil,may lead to interference phenomena, especially for micronutrients. Thiscouldexplainhowsuchtreatmentsassisttheunleashingandgrowthofbacte-rialandfungaldiseases.Giventheprecedingfindings,onemightassumethatthesameholdstrueforviraldiseases.Butbeforeweaddressthisaspectoftheproblem,weshalllookattheeffectsoforganicfertilisers.)

III. Organic fertilisation and viral diseases

Howard(1940)citesacertainnumberofancientagriculturalpracticesinIndiathathelpedimprovetheresistanceofplantstodisease.Hedevotesachapterof ‘An Agricultural Testament’,towhathecalls ‘TheRetreatof theCropandtheAnimalbeforetheParasite.’2Thisex-directoroftheInstituteofCropProtectionatIndore,whowasanagriculturaladvisortotheIndianfederalauthorities,acknowledgeshumblythatheisapupilofthepeasantsinthePusaregion.Asheobserves,‘Theproductscultivatedbythepeasantswereremarkablyfreefromdiseaseofallkinds,’inparticularfromtheviruseswithwhichwearecurrentlypreoccupied.

Lookingparticularlyattobacco,henotes:

‘When carewas devoted to the details of growing tobacco seed, to theraisingoftheseedlingsinthenurseries,totransplantingandgeneralsoilmanagement,thisvirusdiseasedisappearedaltogether.’3

Howardinsistedparticularlyontheimportanceofthewaythesoilisculti-vated.Henoticedthatattacksbycertaincaterpillarswerelocalisedinfieldsthathadbeenflooded.Hewrites:‘Somechangeinthefoodofthecaterpillarhadobviouslybeenbrought aboutby the alteration in the soil conditionscausedbythetemporaryflooding.’4AccordingtoHoward,‘PoorsoilaerationalwaysencourageddiseaseatPusa.’5Thesephenomena,sowell-observedbyHoward,canbeexplainedbythefactthatflooding,bycausingtherootstobeasphyxiated,inhibitsproteinsynthesisandthereforemakestheplantswhichdogrowmuchmoresusceptible.


Excessivedrynesscanhavethesameeffect,sincealackofwaterincreaseslevelsofsolublenitrogeninthetissues,andparticularlyofasparagineandproline[WearingandvanEmden(1967),SlukhaiandOpanasenko(1974),etc.].Outofthis,andalwaysbyanutritionaleffect,comesproliferationofdiseaseandpests,suchasmites.[WearingandvanEmden(op.cit.).]

Conversely,soilthatisadequatelytilledtomakeitwell-aerated,aidsproteinsynthesis by oxygen,which it places at the disposal of the roots, yieldingvigorous,healthyplants.

Howard (op. cit.) also highlights the beneficial effect of farmyardmanureandhumusontheresistanceofplants todisease.Heobserves: ‘Itis a curious fact that in Indore there is no insect-borne disease or cottonfungus.’Furthermore,thisremarkableobserverappearstohavefullysensedthe important role played, in its resistance, by the plant’s conditioningand biochemical state.With specific reference to viral diseases, he notes:‘Inexaminingtheaffectedplants,onemaynoticecertainanomaliesintheproteinmaterial,which leadsone to suspect that the green leaves arenotfunctioningnormally.Nobuild-upofproteinsistakingplace.’

ItisinterestingtocomparetheresultsofthemethodspractisedbyHindupeasantfarmerswiththosepractisedbytheirChinesecounterparts.Chouard(1972),onhisreturnfromastudytriptoChina,wrote:‘

Withoutgoingintodetail,IcansayherethatIhavebeentoldofobserva-tionsmadebypeasants about themostproductivepotatoplants.Thesecome fromplants cultivated in themountainsor even fromplants thatwere cultivated out of season.... The practice of the Chinese peasantfarmers,asrelatedtome,doesnotconsistofdestroyingoreliminatingtheviruses.Instead,theaimistoreduceandsometimestoeliminate,throughcertaincultivationmethods,thedisplayoftheviralsymptoms.Lownighttemperaturesandintenselighthavetheseeffects.Atpresentno-onereallyknows the rigorous scientific basis for the alleviation of the symptoms,withoutthevirusitselfdisappearing.’

Apart from thebeneficial effects of light and low temperatures, organicfertilisersareusedextensively inChina.Wewillnowseehowsomerigor-ouslyconductedexperimentsmayconfirmtheresultsofthousand-year-oldempiricalpracticesinagriculturalmethods,yieldingevidenceofthebenefi-cialeffectsoforganicfertilisers.

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Onemight note in passing that there is sometimes a fine line betweenempiricismandscienceinthestrictsense.Asanexample,wemighttaketheuseofchemicalpesticidesonalargescale,withoutpayingattentiontotheireffectsonthephysiologyoftheplantorthelifeofthesoil.Withchemicalpestcontrolasunderstoodatthemoment,wearedealingwithpureempiricism.For instance, very little is actually known about how the products called‘fungicides’actuallywork.

Regression of a viral disease when organic manure is used.

InTunisia,Mehani(1969)establishedtheexistenceofamosaicvirusintheProvencalvioletartichoke,whoseeffectsareespecially frequent in thesecondandthirdyearsofcultivation,andwhichresultinaconsiderabledropinyield.InFrance,theseartichokesneverdisplaysymptomsofthedisease.Yet if taken toTunisia, theymanifest symptoms of the disease and neverreallyestablishthemselves.

Thisdifferenceinbehaviourhasledtheauthortostudytheeffectofmanureonoutbreaksof theviraldisease.Thestudieswerebasedon the fact that,over seven years, a ‘well-cultivated’ artichoke never displayed symptomsofdegeneration.Thisseemstoprovethat,asinFrance,andduetocertainculturalpractices,theviruscanremainindefinitelyinadormantstate.(Weshallreturnlatertothisideaofdormancy.)

Mehani’s(op.cit.)experimentsshowedthattheuseofmanureallowedapracticalsolutionoftheproblem,byreducingthesymptomsofdegenerationinafairlyspectacularmanner(Fig.4).Weshouldaddthattheeffectoftheorganicmanure is superimposed on that of inorganic fertilisers. It is thejointactionofthesetwotypesoffertilisationthathasprovedtobebeneficialfortheresistance-orifoneprefers,thetolerance-oftheplanttowardtheproliferationandvirulenceofthevirus.

Themechanismatworkonthemetabolismoftheplanttogiveitresist-anceortoleranceisanorganizationofnutritiveelementstopromotebettergrowth.Inotherwords,ametabolismiscreatedthatistheoppositeoftheonecharacteristicoftheviraldisease.Thisdiseasehas,infact,beendefinedasadiseasethatstuntsgrowth.


Fig.4: The influence of farm manure, together with mineral fertilisers, on outbreaks of artichoke mosaic. (According to the figures of Mehani, 1966.)

Asforthedeepercausesbehindthiseffectoforganicfertilisationonthegrowthoftheplantandthusitsresistancetodisease,onecansurmisethat,throughtheimprovednutritionoftheplant,certainmicroorganismsoccur-ring in this typeofmanurearebrought intoplay.Thesituation is just theoppositewithpesticides,whoseeffectsweshallnowconsider.

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IV. Repercussions of pesticides on viral diseases

Manynowaccepttheview,regardingthecontrolofviraldiseases,that‘onetreats theplant andnot thedisease itself.’ (Theoneexception is chemicaldestructionofvectors,whichwewilldiscusslater.)Asaresult,awiderangeofproductshavebeentestedwhicharecapableofactingonthemetabolismoftheplant.Thishasmetwithvaryingdegreesofsuccess,apparentlybecauseitwasnotsupportedbyapreciseworkinghypothesis.

Limassetetal.(1948)carriedoutexperimentsonasmallscaleontobacco,using2,4-DagainsttheXandYviruses.Astheyconcluded, ‘Thehormonespraydidnotpreventinfection,nordiditdestroythevirus.Itsimplyshowedaverystronginhibitingeffectontheproliferationofthevirus.Invitrostudies,moreover,haveshownthattheproductlacksaninactivatingeffectofitsown,whichfullyconfirmsourpointofview.’

However, this effect is temporary: plant stocks given the virus andhormoneatthesametime,andwhichdonotcontaindetectablelevelsofthevirusatthatpoint,displaysymptomsintheuppermostleavesofthetreatedtobaccoattheendofafewmonths.

Inotherwords,thebeneficialeffectonthemetabolismofthetobaccoplantis onlyprovisional.We shouldnot lose sight of the fact that this reactionbetweenplantandpesticidedependsontheinitialstateoftheplant-thatis,onitsphysiologicalstateandthus(aswehaveseenabove)onitsnutrition.

Astotheeffectsof2,4-D,towhichweshallreturn,weshouldaddthattheyarenotalwaysbeneficial.Inthecaseofmaize,spidermitesandcornborersincrease,alongwithsusceptibility to leafstripedisease.Weshall returntothiswhenlookingatcerealcultivation.(OkaandPimental,1976).

However,itistheherbicidesthat,throughtheirspecificanddrasticeffects,providethegreatestinsightintotherelationshipsbetweenthesethreefactors:thepesticide,thephysiologyoftheplant,andtheactivationofviraldiseases.McKenzieet al. (1968-1970)wereable,bymeansof controlled laboratoryexperimentsonresistantorsemi-resistantmaize,toshowthatsusceptibilitytothevirusMDMV(maizedwarfmosaicvirus)increasesinproportiontodosesofatrazine.A100%manifestationofthesymptomsisachievedwithadoseof20ppmofatrazine(Fig.5).


Fig.5: Repercussions of atrazine, according to soil levels, on the level of symptoms of MDVM (dwarf mosaic virus) on corn.

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Alltheevidenceshowsthatthesensitisingoftheplantistheresultofphys-iologicalmodificationoftheplant.Someresearchhasbeencarriedoutonthesubjectofpossibleconnectionswithproliferationofthevirus.MisraandSingh(1975)havestudiedtheeffectsofanumberofchemicalpreparationssuchasgiberellicacid(GA),2thio-uracil,and2,4-Datdifferentdosesonavirusinchrysanthemum(thechrysanthemumstuntvirusorCSV).

One important initial result is that all these chemical products causenitrogenlevelsintheplanttorise,incomparisontocontrols.Wenowknowthatthisisafactorofsusceptibilitytodiseasetotheextentthatthenitrogenisinsolubleform.Inregardtoaconnectionwiththevirus,MisraandSingh(op. cit.) point out in fact that there is no asparagine in healthy tissues,butthat,sixtydaysafter infection, it is foundin leaves infectedwithCSV.Thissuggeststhatthestateofproteolysiscould,aswithotherinfections,beconnectedtoviraldiseases.Thisseemstobeconfirmed,furthermore,bythefactthatproliferationofthevirusdecreasestheamountoffreeaminoacids,aswellaslevelsofpotassium.

This is also evident from the studyof the effectsofherbicidesonplantphysiology,where the cultivated plant is subject to the same attacks, andselectivityisinnowayperfect.ThisisemphasisedbyAltmanandCampbell(1977):

‘Theresults,inthecaseofcarbamateherbicides,indicatethattheuseofaminoacidsbysusceptiblespecies is inhibitedbycarbamateherbicides.Low concentrations of these herbicides are effective: 10ppm of CIPCrepresentapproximately5x10-5molar.Theinhibitionoccursverysoonaftertheherbicidecomesincontactwiththeplant’stissues.’

AsAltmanandCampbell (op. cit.)observed, ‘The inhibitionofproteinsynthesiscausedbyherbicidesmayexplainanumberoftheireffects.’Thisiswhatseemedtobehappeningwhendiseasesincreasedthroughtheeffectofpesticidesonthephysiologyofplants,especiallythatofherbicidesoncerealcrops. Since this is in perfect agreementwith our theory of trophobiosis,theissuemaybesummarisedasfollows:viraldiseases,beingdiseasesthatinhibit growth, arepromotedby anyprocess that inhibits growth.This isespeciallytrueinthecaseofagentsthatcausedeficiencies.


Since all herbicides are toxic for all plants - that is to say, inhibitors ofproteinsynthesis–allmaybecausal factors in thecurrentspreadofviraldisease.Thisisthecaseforatrazine,asmentionedabove.Italsoseemstoexplain the conclusions of Altman and Campbell (op. cit.) in relation toherbicides:

‘Since1945,numerousreportshaveappearedof increased lossesdue toattacksof insectsandpathogens, inspiteofverygreatefforts tocontrolthem.It isdifficult tocalculatetowhatextenttheseareduetotheenvi-ronmentalandbiochemical impactsofherbicides. Inanumberofcasesherbicideshavebeenblamedforcreatingproblemsofparasitisminvariousplants.’

Confrontedbysuchaspreadofdisease,onespeaksof‘resistance.’However,it isnowclear thatwhat is involved isproliferation, causedby theplant’sgreaterreceptivenessasaresultoftheeffectsofherbicidesonitsphysiology.

Forthemoment,wewillnotethatCorsetal.(1971)showedthatoxycar-boxin,whenappliedtobarleyseeds,increasestheleveloftheBrommosaicvirus in the leaves. This fungicide therefore enhances the proliferation ofthevirusbyitsactionontheplant.Yet,aswehaveseenabove,this isnotanisolatedexample:thesameistrueofanychemicalsthatpenetrateplantorganisms and act on theirmetabolism, especially its resistance,which islinkedtothelevelofproteinsynthesis.

V. Grafting and viral diseases. Case Study: the grapevine

However,weshouldsaysomewordsaboutanotherfactorthatalsoaffectsthe‘susceptibility’ofplantstoviruses.Thisistheinfluenceofgrafting.

Souty (1948) concluded: ‘It is not certain that trees which have beengraftedareanymorevigorous,productive,orlonger-livedthanthosewhichgrowfromtheirnaturalroots.’

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This author might also have added: ‘or more resistant to disease.’ AsWallaceetal.(1953)note:

‘Citrusstocksinfluencethesizeofthetree,theharvest,thequalityofthefruit,andsusceptibilitytodisease.’

However, certain combinations of stock and scion can turn out to bebeneficial.Wecansee this fromsomeresultsobtainedbySartic(1975) inobservingSharka,aviraldiseaseoffruittreesthatiscurrentlyontheincreaseinFrenchorchards.

Thisauthorrecallsthatgraftingmayactuallyconstituteavaluablemeansofprotectionnotonlyagainstmycoses suchasPhytophthora parasitica incitrustrees,butalsoagainstmycosisintheappletree(P. cactorum),aswellasagainstrootrotinthepeachtree(P. cinamoni).

Thediscoveryofcertainstocksthatare‘resistant’totheTristezavirus,andofvariouscultivarsusedasapplestocksresistanttoortolerantofso-called‘latent’viruses,enablesustoenvisageanelegantsolutiontotheproblemofdiseasecontrol.Naturally,thisisonlypossiblewheretheuseofthesestocksiscompatiblewiththeotheragronomicconstraints(production,fruitqualityetc.).

However, harmful effects of grafting in connection with viral diseaseareequally striking,andsometimesarise ina rather insidiousmanner,asMarrou(op.cit.)notes,inconnectionwithviralmaladiesincropsformarketgardening.Thiswouldalsoappeartobethecasewiththegrapevine,wherewehaveseenapotentialrelationshipbetweendeficienciesandviraldisease.

Theincreaseofvirusesinthegrapevineprovidesmanylessons.Itisverycloselylinkedtoanother‘affliction,’theinvasionofPhylloxeraandtheagro-nomicsolutionwhichhasbeenfound:theregenerationofthevineyardsbygraftingFrenchplantsontoAmericanstocks-Riparia, Rupestris,andtheircrosses.

AsRives (1972)notes, ‘Theproperties of the stocks are communicatedtothescionor,atleast,tothewholeplant.’Rivesstresses:‘Fromtheresultsobtainedfrommultiplecombinations,thereisnowaythatwecanpresumetodifferentiatebetweenthosewhichareduetothestockandthosewhichareduetothevirus.’


Butistherenowayofgaininganideaoftherelationshipbetweenstock,scion,Phylloxera,andvirus?Eveninthecontextof‘susceptibility’tovariousafflictionsandthebiochemistryofthescion?

Hereweencountertheroleofvectorsinthespreadofviraldiseases.Theyhavebeenthesubjectofcontroversy.Atthethirdinternationalconferenceonwinemakingand thegrapevine.FatherBranasdeniedeverhavingsaidthatPhylloxeraisaninsectvectorofviruses.However,ashestated, ‘ThereisadirectrelationshipbetweenthespreadofPhylloxeraandthespreadofviruses.’

In response to this, Father Ciferri observed that this might be due totheuseofAmericanstockswhich ‘upset’ thebalance(probablyanancientone) betweenVitis vinifera and theclassic infectiousviruses ofdegener-ation. Ciferrimaintained that such viruses do not cause obvious damageto European grapevines that are not grafted on to American root stocks.However, cultureswithAmerican root stocks, even those that haveneverbeenincontactwiththeviruses,unleashedthediseasewiththegravityseeninthelastdecadesofthenineteenthcentury.Fromthatpoint,theyinfectedtheparabiosisoftheEuropeangrapevinegraftedontoAmericanroot-stock.

ThoughVitis viniferaissensitivetoPhylloxera,itprovesresistanttochlo-rosis(that is, irondeficiency). Iron-inducedchlorosis is thesymptomofadisorderofironmetabolism,causedbylimestonesoils.Ungraftedgrapevineswere tolerant of chlorosis, either because of their low iron requirementsorbecausetheirrootswereabletomaketheironinthesoileasilysoluble.‘However,afterPhylloxerahaddestroyedthevineyardsduringthelastcentury,itwasnecessary tograft thegrapevineson to stocks (ofAmericanorigin)whichwereresistanttotheparasite.Yetsomecombinationsofrootstockandvinethenshowedthemselvesmuchmoresusceptibletochlorosisthanvinevarietieswhichwerecultivatedontheirownroots.Theironrequirementsoftheabove-groundsystemofsuchcombinationscouldnotbesatisfiedbytheweakabilityofsomerootsystems(ofthestock)toextractironfromthesoil.’(ApersonalletterfromM.Delas,INRA,Bordeaux).

Basically,graftingledtoirondeficiency.Couldthisbeasufficientreasonforthesusceptibilityofthevinetoaviraldiseasesuchasinfectiousdegener-ation?Thereisnoreasonwhyanirondeficiencyshouldnotbeaccompaniedbyseveralotherdeficiencies,suchasboronorzinc.

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Inconfirmationoftherelationshipbetweenviraldiseaseanddeficiencies,Dufrenoy (1934) demonstrated experimentally that sprays based on zincsulphatecausedsymptomsofgrapevinefanleaf(infectiousdegeneration)todisappear.WeshallreturntothisimportantissueofthetreatmentofdiseasesthroughcorrectionofdeficienciesinthecourseofChapter8

VI. The works of Vago and the concept of disease

Intheintroductiontohisthesis‘TheProgressionofDiseasesinInsects.’6onthesubjectofthegeneralconceptofdisease,Vagowroteasfollows:

‘Aftermorethantwocenturiesofresearchineverydomainofpathology,aiming todefinepathologicprocessesasmorbidentities, there isanewtrend that acknowledges the difficulty of trying to explain numerouspathologicstatesonthebasisoftheisolatedunitcalled‘disease’.’

Alittlefurtheron,Vagoadds: ‘Itseemedtousthatthedomainofinsectpathologymightpossiblymakeaspecialcontributiontowardimprovingourknowledgeofthisnewpathway.’Thereisastrangeconvergencebetweenhisconclusionsandthenotesthatrelatetotheprocessesofdisordersinplants.Atthispointwearepersuadedtoacknowledgeagenerallawofbiologythatappliesinequalmeasuretothereactionsofplantandanimalorganisms:thatis,thebalancebetweenhealthanddisease.

Vago’sworkbeganwiththestudyofaproblem.Intheyearspriorto1950,jaundice of silkworms raged in a well-demarcated area within the Gard,ArdècheandLozèreregions.Thisareawasborderedtothenorthbyachem-icalfactory,andthegravityoftheoutbreakwasdirectlyduetotheproximityofthefactoryandthedirectionoftheprevailingwind.

Moreover, caterpillars reared on the leaves of themulberry taken fromthisareaclearlyconfirmedthatthistypeofdietpromotedthespreadofthedisease.Infact,only2%polyédriewasrecordedonadietofleavesgatheredoutside thecontaminatedarea,while thisrose to20%(a tenfold increase)withleavescollectedinthecontaminatedarea.


Anotherimportantpointisthatadietofleavesentirelyfromthecontami-natedareayieldedthefollowingresults:

• 13%polyédriewithleavespreviouslywashed.• 23%polyédriewithunwashedleaves.

Sucharesult suggests thatpesticides in the formof residues, importantthoughtheyare,arenotthesoleculprits.The13%polyédrieresultingfromadietofwashedleaves,butwhichhadbeentreatedwithpesticides,stoodincontrastto2%whenhealthyleaveswereused.Thisshowsthatthepesticideinquestion(NaF)hadaneffectafterpenetratingtheplanttissues,byharm-fullymodifyingtheplant’sbiochemistry.

This jaundicewas in factprovokedby the ingestionof sodiumfluoride(NaF),theessentialconstituentoftheemissionsfromthefactoryinques-tion.Vagomade comparisonswith cattle fluorosis that raged in the sameregion,andwithasimilarcaseinItaly.

Thisisacaseoftheunleashingofaviraldiseasebypoisoning.However,Vago’sstudiesalsodealwiththeeffectsofdiet.

ThusVagoshowedthat,inthecaseofLepidoptera Vanessa urticae L.,atleasttwotypesofdietpromotethedevelopmentofpolyédrie:

• along-termdietofwitheredmulberryleaves,containinglittlechloro-phyllandintheprocessofyellowing.

• adietofnettles,whichhasdifferenteffectsonthepolyédrie,accordingtothetypeofsoilfromwhichtheplantsaretaken:

• fed on nettles from clayey soil, the youngest larvae show levels ofpolyédrieof15-19%.

• fedonnettlesgrowninanarablealluvialsoil,younglarvaeonlyshowalevelof4%.

Such indirect effects caused by the plant recall the differenceswe havealreadypointedoutinthefertilityoftheColoradobeetle,orintheresistanceofplantstodiseaseaccordingtosoiltype.

Vago confirmed, in hisworkwith silkworms, the results obtainedwithVanessa urtica.Whenfedonveryripemulberryleavesthewormsproduce,fromthefirstmoulting,ahighpolyédrie,andthedisorderpersiststhroughoutthewholelarvalstage.

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Such experiments clearly underscore the great importance of diet andnutritionfortheresistanceoforganismstopathogenicagents.Itisnaturaltodrawaparallelwiththeeffectsofdifferenttypesoffertilisersontheresistanceofplants,bothtoinsectpestsandtodiseases.

Provocation of viruses in silkworms in the absence of previous infection.

By takingmanyprecautions,Vagowasable toexcludeany introductionof the virus.The experiment concerned a food that silkwormswouldnotusuallyfeedon:Maclura aurantiaca(osageorangeorbowwood).Comparedwiththeirnormaldiet-Morus albaorwhitemulberry–theresultswere:

• lessfoodingested• ahighermortalityrate• finally,developmentofavirosis.

Fromthethirdgenerationon,thepolyédriewasintensifiedintheMaclurabatch.Duringthefourthandfifthgenerations,thediseasepracticallyelimi-natedthewholebatchthroughaprocessofnymphosis.Amongthecontrols,however,mortalityremainedunder20%.

However,perhapsthemostsignificantexperimentswerethosewithadietincludingsodiumfluoride.Totracethese‘secondary’effectsofthepesticide,itwasessentialtoachieveonlyasub-lethalaction.Forthisreasontheleavesofthemulberryweresoakedina0.01%solutionofNaF.(Thiswasanexper-imental version of what had been observed in the natural environment.)Theseresultsweremoreconclusive:

• dietofcontaminatedleaves:85%viroses.• dietusinghealthyleaves:8%viroses.

From the thirteenth day onward, the virosis became significant. Thediseasecurveshowedarapidandtotallossofthebatch.

Onthebasisoftheserigorousexperiments,Vago’sconclusionsbecomesoimportantthatwereproducetheminfull.Ashesaysattheoutset:‘Itappearspossible to trigger an acute virosis without previous infection and in thecontrolledabsenceofanysignofvirus.’ Vagoadds:‘Theunderlyingfactorsmaybe linked to diet, to poisoningby certain chemical substances, or toclimaticandphysiologicalconditions.’


Conversely,thefactorsbehindnon-appearanceoftheviruscorrespondtoanoptimumphysiologicalstate,freeofanydisruptionofapathologicalorparapathologicalnature.AsVagonotes:

‘Thesetwoconsiderationssuggestthatthefactorsbehindthetriggeringofthevirosisarephysiologicaldisturbances.Inspiteofthevariednatureoftheirexternaleffects,thesemayhaveincommonaspecificmechanismatthecellularlevel.’

InVago’swords:‘Theunleashingofvirosesbynon-infectiousfactorsseemstoustohavetheformofacomplex.Thefirststageofthiscomplexconsistsofvariouspathologicalprocesses,whilethesecondstageisrepresentedbythevirosis.’

AsVagoobserves,‘Virosesaretypicallysecondaryinthecaseofmetabolicdisturbances.’Hecontinues:

‘Theappearanceofvirosesfollowingvariousprimaryprocesseswhichseematfirstsightquitedifferent,turnsouttobeverycloselylinkedtodeviationsincellularmetabolismthatfollowtheseprocesses.Heretheinnermecha-nismissetinmotionbyreactionsoftheintra-cellularenzymes,inrelationtoapre-existentelementwithviruspotential.Theproblemposedbythismechanismhasbeenlikened,incomparativepathology,totheinductionofbacteriophagesor‘dormantviruses’inplants.’(Nowadayswespeakof‘latentviruses,’thoughtheprocessisthesame.)

Vago emphasises, moreover, that in this cause-effect chain ‘metabolicdisturbances viroses’ theprimaryeffects followuponeitheradiet thatleadsprogressivelytoastateofimbalanceor,instead,atoxiceffect,inwhichthedoseisdecisive.Thus,todeterminethecomplexesinducedbysodiumfluoride,wewouldneedtoestablishadosecorrespondingtoeachgenerationandeachraceinthestudy.

Thesefindingsaboutcomplexesof‘disease’ininsectsleadustoconsidertheir general applicability . As we have just seen, Vagomakes a case for‘dormantviruses.’Returningtothisinhisconclusions,henotes:‘Analysisof this complex (metabolicdisturbanceswithdelayedappearanceofacuteviroses)hasintroducedsomeelementsnowwell-assimilatedintocompara-tivepathology.

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Along with bacterial lysogeny, ‘dormant viruses’ in plants, and theDrosophila virus it raises the issue of viral induction without previousinfection.’

AccordingtoPoljakov(1966),whoalsoseesthephysiologicalstateofthehostplantasoneoftheprincipalfactorsdeterminingtheresistanceofcryp-togams,dithiocarbamatesareresponsibleforunleashingvariousdiseases.Hewrites(op.cit.):

‘Wehaveobservedanimpactoforgano-chemicalsonthedevelopmentoffungaldiseasesinappletreesandgrapevines,wheretheuseofzinebinthecontrolofapplescabandmildewpromotesthedevelopmentofOidium.DithiocarbamicacidusedoverfouryearstocontrolofPhytophthorainpotatoesalsoprovokesanincreaseofotherdiseases,especiallyviroses.’

These observations confirm our own research into the sensitisation ofplants toOidium in grapevines bydithiocarbamates (Chaboussou, 1966).Theexistenceofacompleximpliesbothanattackofpathogenicfungiandaviralattack.

However, we have seen that other pesticides, especially certain herbi-cides suchasatrazine,maymakeplantsmoresusceptible toviraldiseases(McKenzie et al., 1970). Since such effects may be combined with thoseofmalnutrition brought on bymistakes in fertilisation, such as excessivenitrogen,itishardlysurprisingthatthereiscurrentlyanincreaseindiseasesofcereals,suchasDwarfbarleyyellow.

Thedeepercausesofthisphenomenoncouldlieinthemannerinwhichdeficienciesareinduced.Vicario(1972)notedthatpesticideswithanitrogenbase(i.e.themajorityofchemicalpesticides),arecations.Assuch,theycandisplaceothercationsintheinterchangeablecomplex,suchasCa,Mg,andZn.Certainfindings(Huguet,1983)seemclearlytoconfirmthis.

Clearly,then,thequestioniswhethersuchadeficiencycanalterthemetab-olismoftheplanttothepointofprovokingaviraloutbreak.Wemustnotforget thataviraldiseasediseaseaffectsgrowth,andwill thereforebenefitfromanyfactorwhichinhibitsgrowth.Deficienciesfallintothiscategory.WerecallthatDufrenoyshowedthatinbroadbeansaborondeficiencycausesachangeinthecore,tothepointwhereittakesonafilamentousaspectinthemeristems.


All this seems toshowclearly,onceagain, thegreat importanceofdefi-cienciesinoutbreaksofdisease,especiallyviraldiseases,inthecontextofametabolismdominatedbyproteolysis.Thisviewissupported,asweshallseeintheeighthchapter,bythebeneficialresultsofcorrectingdeficiencies.

It also explains the difficulties in eliminating viral diseases if one doesnottakeintoaccountthecomplexofeffectsonthemetabolismoftheplantbroughtaboutbytheuseofchemicalpesticidesandfertilisers.Weintendtoprovideadditionalproofofthisinthenextchapter.

Notes1 Phomabetae =Pleosporabjoerlingii =Fr.PiednoirdelaBetterave;maladieducoeur =E:seedlingrotrot,leafspot,BlackRot ofgrowingroots,Heartrotofmatureroots.2 SirAlbertHoward,AnAgriculturalTestament(NewYork,London:OxfordUniversity

Press),1943,253pp.[republished:RodalePress,1976,253pp.]:titleofChapterXI.3 Howard,op.cit.,p.163.[ChaboussouhastranslatedHowardratherfreely.]4 Howard,op.cit.,p.164.5 Howard,op.cit.,p.162.6 C.Vago,L’enchaînementdesmaladieschezlesInsectes.(ThèseFac.Sciences,Aix-

Marseille),1956,184pp.

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Chapter 6

Relations Between Viral Diseases, Vectors (Aphids) and Pesticides

I. What makes viral diseases exceptional?

It is frequently said that viral diseases are generalised, incurable, trans-mittedbygrafting,variableinsymptoms,andimmunetoanydefencemech-anismoftheplant.

However, ifwe examine thesedifferent ‘properties’ closely,we shall seethattheyarenotuniversallyapplicable.Certainplantsofthesamespecies,depending upon their age and stage of development, refuse to becomecontaminated.

Incurable?Yes,butonlyifoneseekstodestroythepathogenicagent,thatis,thevirus.Notif,asweshallseebelow,onetakescare,throughnutritionalandprotectivemeasures,topreventthevirusmultiplyingorevenreplicatingitselfinthecell.

Transmitted through grafting? Certainly, but only if the ‘combination’of rootstockand scionallows replicationof thevirus.Thisunderlines theinfluenceoftherootstockontheviraldiseaseviathephysiologyofthescion.(WeshallcomebacktothisinChapter7.)

Variableintheirsymptoms?Yes,ithasbeenpointedoutthatviralinfec-tionshavefewtrulycharacteristicsymptoms.However,whilefewsymptomscanbestrictlyassociatedwiththem,thereisastrongconvergencebetweensymptomsofnutritionalproblems,forexample,andviralinfections.

Thisistobeexpectedbecausenutritionandtoxinsbothaffectthephysio-logicalstateoftheplant,andthusitsresistance.

115 Relations Between Viral DIseases, Vectors (Aphids) and Pesticides

Environmentalfactorsplayaroleinviralaswellasbacterialandfungalinfections,aswellasinattacksbypests.However,whatseemtocharacteriseviraldiseasesaretheeffectstheyhaveatthecellularlevel.Theseeffectsarebroughtaboutbymetabolicproblems,themselvestheresultofmalnutritionortoxins,orbythegenesis(oratleastthemultiplication)ofthevirus:DNAorRNA.

Theusualapproachtocontrollingviraldiseasesistoseekthedestructionof thevectors (aphids, leafhoppers,nematodes, etc.)This isdonewithoutany regard for the physiological state of the plant thatmay condition its‘receptivity’tothevirus,orforthenegativeeffectsofpesticidesonthemetab-olismofthecropsoneseekstoprotect.Thisliesattherootofthefailureofchemicalstocontrolthevectors.Thesechemicalproductsarelikelytocausethem tomultiply, and to aggravate thediseases by the sameprocess, as aresultofincreasingtheratioofproteolysistoproteinsynthesis.

II. Chemical control of vectors

1. The failures of aphicide treatments

Numerous researchers have found that the chemical control of vectorsis extremely disappointing. As Marrou (1965) notes, ‘Direct control byinsecticidesprays,thoughitdestroysthevectors,doesnotingeneralprotectthecropfromviruses.’Hepointsoutthatforthemajorityofvirusesofthemosaicfamily,tobepiercedoncebyanaphidisenoughtoinfecttheplant.Evenifthisfirstcontactwiththeplantproveslethalforthevector,thevirushasbeenpassedon.

The facts, however, seem to be more complex. In particular, chemicalcontrolisblamedfordeterringinsectsandsodispersingdisease.However,the mechanism of these failures may lie deeper. After a brief period ofeffectiveness, many pesticides increase the numbers of aphids instead ofdestroyingthem.Themechanismforthisproliferationdoesnotliesimplyinthedestructionofnaturalenemies,aswementionedinthecourseofChapterII.

Münster and Murbach (1952), in treating the potato plant with thephosphoricester‘pestox,’foundthatthelargestpopulationsofaphidswerefoundonthemostfrequentlytreatedplots.Moreover,thestateofhealthoftheplantsharvested fromthe treatedplotswasnotsuperior to thatof theseedlingsintheuntreatedplots.

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The authors attribute these results to insufficient toxicity in the treatedplants, and a greatermobility of aphids on those sameplants.Theywerenot able, however, to comment on the proliferation in proportion to thetreatments.

BoveyandMeier(1962)likewisefoundthatchemicaltreatmentsbasedonlimearsenate,carbaryl,DDT,anddieldrinledtoanincreaseinthenumbersofleafaphids.Theyseethecauseforthisintheeliminationofpredators,oraphid-phages.Buttheyalsoobservethatonecauseisinsufficientactionofthechemicals,becausetheaphidsmultiplyrapidlyonthelowersurfacesoftheleaves.Thissuggestsanotherphenomenon,ofanindirectandnutritionalnature.

Theauthorsadvisekeepingchemicaluseagainst theColoradobeetle toastrictminimum,inorder,theysay,topreventamassiveincreaseinviralinfections.

Similarfailuresoccurinthecontrolofpotatowhorlbydiazonontreatments,orMyzus persicaebyschradantreatments.Twoweeksafterthetreatment,theaphidpopulationsinthetreatedplotswerefourtimeshigherthanthoseinthecontrolplots.Here, theauthor thinks that the increase indiseaseandreductioninyieldwerelinkedtotheupsurge,afterthechemicalapplication,ofthepopulationofwingedandwinglessaphids(Klostermeyer,1959).Butheretoo,anotherfactorplaysapart:theactionofthepesticideonthepotato.

In regard to controlling potato Y virus, Shanks and Chapman (1965)obtainedequallydisappointing results.They foundoneparticularlyunex-pectedeffect:onplantstreatedwithparathion,theaphidssurvivedtwotothreetimeslongerthanonthecontrolplants.

Webelievethisshowsthatthepesticidehasalteredthemetabolismoftheplant(inthiscase,tobacco).Theresultisamuchgreaterimpactontheviralinfection,althoughtheauthorsmakenodistinctionbetweentheroleoftheaphidsand thatof theplant’sphysiology. In linewith the ideasofRussell(1972), one can assume, as a first approximation, that resistance to viralinfectionismadeupof:

• resistancetotheaphidvectors• resistancetoinoculationbythevirus• andfinally,tolerancetowardthevirus.


Allofthesefactorsareintegratedintheworkingsofthecomplex,Plant-Pesticide-Virus-Vector.WehavegainedaninitialdemonstrationofthisfromtheexperimentsofRoland(1953).

Theaimoftheseexperimentswastostudytheinfluenceofrepeatedaphi-cidesprays,withthehelpofachemicalwithpersistentaction,onthestateofhealthofapotatocrop,consideredpurelyfromavirologicalpointofview.TheseexperimentswerecarriedoutonthepotatovarietyAckerman,whichwasinitiallypropagatedinisolationinagreenhouse(aftereliminatingplantsinfectedbywhorl,theXvirus,ortheYvirus).Thesewerethereforenotrepre-sentedinthetuberssubjectedtotheexperiment.However,thepotatoeswereplantedintwoplotsthatalreadycontainednumerousplantscontaminatedwithwhorlandYvirus.

Whileoneoftheseplotswastreatedontenseparateoccasionswitha0.1per1000solutionofparathion,theotherremaineduntreated,toserveasacontrol.

Atharvest,twotuberswerekeptfromeachplantinthetwoplots.Thesewerere-plantedthefollowingyear,havingbeenkeptfreeofaphidsduringthewinter.Twoweeksafterthefirstshootsappeared,thenumberofdiseasedspecimenswascounted.Asaconsequence,thediseasecouldbeattributedtothemotherplantbeinginfectedbyaphidsintheprecedingyear.Table8givesthedetailsoftheresults:

Table 8: Plants with Viruses in Relation to Treatments

Viruses Treated plot Control plot

N % N %

Plants with virusesWhorlMosaic

3331 3

8377 7

2117 5

504012

Totheauthor’ssurprise,notonlydidtherepeatedparathiontreatmentshavenobeneficialeffectsatallonthestateofhealthof thetreatedtubers,buttherewasalsoanincreaseintheproportionofwhorlinthetreatedplot.Roland(op.cit.)deducedfromthisthatthepesticideattractedtheinsects.

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ShanksandChapman(1965),whocarefullystudiedtheeffectofvariousinsecticidesonthebehaviourofMyzus persicaeinrelationtotransmissionofthepotatoYvirus,foundthataphidsstayedaroundtwotothreetimeslongeronplantstreatedwithparathionorphoratethanonthecontrolplants.

Theyconcluded,moreover, that theseexperiments showedwhy insecti-cideswerenotabletopreventthespreadofdiseasebyaphidsinthefield,andwhytheycanevenbelinkedtoanincreaseininfection.

Thereasonforthisbecomesevenclearer,asweshallseelater,whenweconsiderthatbothparathionandmevinphoshaveatendency,throughtheiractiononthemetabolismoftheplant,toleadindirectlybythetrophicroutetoproliferationofaphids.Thisprocessisanalogoustotheonewewereabletodemonstratewithmites(Chaboussou,1969).

Suchaggravationofthedevelopmentofviraldisease,bypesticidessuchasparathion,recallsourdiscussionof‘fungicides’suchasdithiocarbamates(zineb),whichalsoaffectpotatoes(Poliakov,1966).

2. Proliferation of aphids due to pesticide treatments.

Numerousauthorshavepointedouttheresponsibilityofpesticidefortheproliferationofaphids.Asearlyas1946,MichelbacherfoundthatDDTledtothemultiplicationofChromaphis juglandicola(Kalt)aftertreatmentagainstnutCarpocapseonwalnuttrees.ItshouldalsobenotedthatDDThasthesameeffectonthecaterpillarLecanium pruinosum(Coquillet).

Pimental (1961) likewise notes that the use of DDT results in largerswarms ofRhopalosiphum pseudobrassicæ on the cabbage plant. Peterson(1963)observesanincreaseinMyzus persicæonthepotatoplant,notonlywithDDT,butalsowithcarbaryl,Gusathion,andDi-systom.

According to Granet and Read (1961), carbaryl is also responsible forincreasing the numbers of Rh. pseudobrassicæ on the turnip plant, andaccordingtoThurston(1965),forproliferationsofM. persicæontobacco.

With regard to organo-phosphate insecticides, their promotion ofmitepopulations have been reported many times. Fenton (1959) found thattreatinglucerne(alfalfa)withmixturesbasedonparathion,toxaphene,anddemetonledtoincreasesinpopulationsofMacrosiphum pisi.

I.Redenz-Rüsch(1959)foundthattreatingappletreeswithparathionanddemeton throughout the year resulted in larger populations ofmites andaphidsattheendofthegrowingseason.


Thisisthemoresurprisingasthesepesticidesareespeciallyactiveagainsttheseparticularpests,atleastintheshortterm.

Steiner(1962),whomadeaclosestudyoftheeffectsofvariousinsecticides,bothmineralandchemical,onawholerangeofnoxious insectsonappletrees, found very significant multiplication rates of aphids with productssuch asmalathion, Thiodan, parathion, andDDT. Increases in Aphididæwerealsofoundwithdemeton,Diazinon,andleadarsenate.

Until now, our discussion has focused on the effects of insecticides.Traditionaltheories-despitethedemonstrationsofmultiplicationbytrophicmeansthatwewilldiscusslater-holdthatproliferationisduetothedestruc-tionofnaturalenemies.Thismustbecarefullyexaminedwhen lookingatthewidespreadproliferationofaphids,duetothesyntheticpyrethrumsusedagainstPyralesattackingmaize.Thephenomenonisequallyprevalentwithfungicides.

Repercussionsoffungicides.Manyfungicidesareharmlessforthepreda-torsandparasitesofaphids.Thismakestheireffectsonaphidpopulationsallthemoreinterestingtostudy.

Steiner(op.cit.)recordedasignificantincreaseinAphididæontheappletree,aswellasinpsyllids.Thisoccurredaftertreatmentsofcaptanandofthiramor(Accordingtoourresearch,captanisalsoafungicideparticularlypronetoincreasingmitepopulations.)

In linewith theseobservations,Hukusina (1963) foundon apple trees,particularlyattheendoftheseason,agreatabundanceofmitesandaphids,followingtheapplicationofaseriesoftreatmentswithchemicalsthatwerenotespeciallytoxictonaturalenemies.Thiswasparticularlythecasewiththecombination:leadarsenate-captan.

It was, moreover, Hukusina and Ando (1967) who, following theirpreciseobservations, related the fecundityof theaphidMyzus malisinctus(Matsumuru)tothenutritivequalityoftheappleleaves.Theywereabletoestablish:

• that the aphidspreferred the shootsof treeswhen the treeswere inthegrowingprocess,inotherwords,whentheywererichestintotalnitrogen;

• thisrichnessinnitrogenexplainedthegreatersusceptibilitytoaphidsof the varietyDelicious in comparisonwith the variety Ralls Janet.(Thishelpstoconfirmthatnitrogeninfluencessusceptibilitytoattacksbydifferentparasites.)

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Resultswithplantsgrownincontrolledenvironments,andthusbeyondanypossibleinfluenceofnaturalenemies,furtherconfirmthishypothesis.

3. Stimulation of aphid fecundity by trophic means, following pesticide treatment.

MaxwellandHarwood(1960)areperhapsthefirsttohavelookedattherelationbetweenplantfecundity/physiology,andtheeffectsofpesticides.These authors found that the application, under laboratory conditions,of2,4-Don thebroadbeanplantmarkedly increased the reproductionofMacrosiphum pisum(Harris).SimilarresultswereobtainedwithMelanoplus bivittatus.

Leaf analysis has shown that where aphid development is greatest, themostnotablebiochemicalchangesareintheratiosoffreeaminoacids.2,4-Dincreasesthefreequantitiesofalanine,serine,andglutathione.

Smirnova(1965)wasabletolinkthemultiplicationofAphis fabaeonthebroadbeanplantundertheinfluenceofDDTwithincreasesinthetissuesofnon-proteicnitrogenanddisaccharides.Thesechangesoccursomeeighttofifteendaysafterapplication.Theauthorconcludes,‘Theaphidpopulationincreasesasthelevelsofnon-proteicnitrogenincrease.’

WefindthesameconvergenceofresultsandthesameconclusionswithChan (1972).He has experimentedwith Schizaphis graminum on barley,examiningtheplant’sresistanceaccordingtovariety.Asdiscussedabove,themostvulnerablevarietiesofappletreeshowedthehighestconcentrationsoffreeaminoacids.Thesameisalsotrueoftotalsolublecarbohydrates.

The results resemble those ofMichel (1964) in regard to the effects ofmevinphos and phosdrine on the multiplication rates ofMyzus persicae,subsistingon treated tobaccoplants.He records an increase in fecundity:from a rate of 25.09 on the control plants to 31.69 on the tobacco plantstreatedwithmevinphosataconcentrationof1mlperlitre,andto46.30onplantstreatedwithmevinphosataconcentrationof2mlperlitre(fig.6).

Inadditionlifespanisprolongedaccordingtothetypeoffeed:69.60daysonthecontrolplants,74.40daysforaphidslivingoffplantstreatedatconcen-trationsof1ml/l,and87.43forthoseonplantstreatedataconcentrationof2ml/l.Theresultsarequitesimilartothoseweobtainedwithmites.


Fig.6: Fecundity and generational succession of Myzus persicae reared on tobacco treated with mevinphos (at two dose levels) and on controls. (Michel, 1964.)

Furthermore, thenatureofaninsect’snourishmenthasaneffectontherateofitslifecycle.Asaresultofthealterationofthefoliagebythepesticide,theaphidsarelikelytoreproducemuchearlier.FromJulytoNovember,theresultistheappearanceofanadditionalgenerationofaphids,whentheyarefedonfoliagetreatedwithmevinphos.

These results also tally with those obtained by Kessler et al. (1959)concerningtheeffectsofpurinesonthemetabolismofnitrogenintheleaves,inconnectionwiththeplants’‘susceptibility’toaphids.TreatingtheleavesofappletreeswithcaffeineleadstoareductioninthefecundityofAphis pomi.Caffeinedoesnothaveanydirecteffectthroughcontactwiththeaphid,nordoes it work through ingestion. It must therefore work indirectly via thechangesitinducesinthemetabolismoftheleaf.

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Analyseshaveshownthatcaffeinelowerstotalnitrogenlevels,particularlythesolublefractionandtheDNA,whiletheproteinfractionandtheRNAincreaseinlinewithincreasesinthecaffeinedose.Theactionofthecaffeineandthatoftheageoftheleafinrealitymirroroneanother:inbothcases,theRNA/DNAratioandproteinsynthesisrise,whilelevelsofDNAandsolublenitrogendecrease.

The reduction in aphid development comes from these changes in theleaf’sbiochemistry,whetherthechangesarenaturalorartificiallyinduced.Theresistanceofmatureplants,ashasalreadybeendiscussed, is ineffectexplainedby the increase inrelative levelsofRNAandproteins.With theapproachofsenescence, theopposite is thecase: theproteolyticprocessesaccelerate,togetherwithdecompositionofproteinsanddestructionofRNAandDNA.Theseanabolicreactionsreleaseconsiderablequantitiesofsolublenitrogen,aphenomenonlinkedtotherenewedvulnerabilityoftheplanttoattackbyaphids,aswellastotheirproliferation.

4. Nutritional requirements and fecundity of aphids

Considerableprogresshasbeenmadeoverthecourseofrecentyears indetermining theneedsof aphids, thanksmainly to techniquesof artificialrearing.WereferheretotheworksofAuclairandhiscolleagues(1957,1960,1964)onthepeaaphidAcyrtosiphum,andofMittlerandDadd(1963-65)onthesubjectofMyzuspersicae.WemustalsomentionOrtmann’sstudies(1965)onalfalfaandpeaaphids,andthoseofWearing(1967)onAphisfabae, Myzus persicae,andBrevicorne brassicae.

It emerges from this collection of studies that aphids require differentoptimumdiets,dependingonthespeciesandeventheageoftheindividual.However,theseshowacertainbalancebetweenaminoacidsandsugars.Ontheirown,aminoacidsproveincapableofinducingnutritionalresponsesinMyzus persicae.Ontheotherhand,theycanactsynergistically,incombina-tionwithsugars(MittlerandDadd,1964).

Inageneral fashion,however, asAuclairhas shownwithAcyrtosiphum pisum,theaminoacidsareinquantitativecorrelationwiththegrowth,devel-opment,longevity,andreproductionoftheaphids.

MittlerandDadd(1964),moreover,notethattheconcentrationsofaminoacidsandamidesinthebeanplantaregenerallylowerthantheminimumrequiredforthehealthygrowthofaphidsonasyntheticdiet.


Thesefindingswouldappeartobeinlinewiththemultiplicationofaphidsafterpesticidetreatmentswhich,byinhibitingproteinsynthesis,enrichtheplantinthesenutritionalelements.Suchmetabolicchangesalsoseemrelatedtotheplant’sincreasedpowerofattraction.

5. Factors determining the aphid’s selection of its host

Herewe encounter a fundamental problem. Lipke andFraenkel (1956)quitejustifiablypointoutthattheaphid’spreferenceforcertainhostsconsti-tutesthetrueheartofagriculturalentomology.Kennedy(1965),forhispart,whilerecallingoldprinciplessuchas‘Ahealthyplantisanimmuneplant,’or‘Thenutritionalconditionofthelarvadeterminestheimago’segglayingchoices’,counselsustodistrustover-hastygeneralisations.

Aphidrelationswithplants,forinstance,arecomplicatedstillfurtherbythefactthatdifferenthostsarechosenatdifferentseasonsaccordingtodifferentstagesoftheinsect’sdevelopment.However,Kennedy’sownstudiesonAphis fabaeimplythataphidschoosetheirfoodinresponsetothenutritionalfactorsmadeavailablebytheplant.Thisappearstoexplainthisspecies’preferenceforeitheryoungleavesorsenescentleaves(acharacteristicsharedequallybyMyzus persicae).Inotherwords,itshowsapreferenceforplantpartsrichinsolublesubstances(saccharoseandaminoacids),whichguaranteetheinsectbetterreproductioninrelationtoitsnutrition.

Notlongago,thisstatementwouldhaveseemedtocontradictthetheorythatwaspreviouslywidelyaccepted,accordingtowhichthechoiceoffoodbyphytophagicinsects,whenspecific,wasgovernedlargelybyresponsestonon-volatilechemicalssuchasvariousessentialoils,alkaloidsetc,actingastokenstimuli.

While it cannot bedenied that theseelementsplayapart inattractingtheinsecttothehost,theyareinfactonlyby-productsofametabolismthatassures the insect of the nutritional elements it needs for its growth andreproduction.

Theseviews,whichcertainresearchersdistrustbecauseoftheirapparentfinalism,appeartobeconfirmedbyrelativelyrecentresearchthatexaminestheresponseofaphidstoartificialdietsascarefullyastheresults- that is,their proliferation as a consequence of certain pesticide treatments of thehostplant.

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Fig 7: The development of Aphis fabae on the sugar beet, with or without mosaic virus.

A) On five plants of each kind, the mosaic was inoculated 18 days before contamination by aphids.B) Four plants of each variety, with mosaic inoculated 12 days before contamination by aphids.f2, f3: reproductive generations.

(after Kennedy)


Numerous studieshave shown, ineffect, thatnutritional substancesarelinked to the mechanisms of phagostimulation in phytophagic insects,particularlyforaphids.Auclair(1965)notesthatpreferencesandfecunditygotogetherinthecaseofA. pisumfedonanartificialdiet.Inthiscaseprefer-encesandsurvivalarenotcorrelated.Thereisadifferenceinbehavior,inthisrespect,betweentheyounginsects,whichpreferadietrichinsugars(35%saccharose),andtheadults,whichchooseadietlessrichinthissubstance(20%),butonewhichalsobringsthemgreaterlongevityandhigherrepro-ductionrates.

In consequence of their experiments in growingMyzus persicae withanotherartificialdiet,MittlerandDadd(1965)concludethatfromnowon,‘WecannolongerconsiderKennedy’sviewsasabsurd’.

Butwhathappenswhenweintroduceanew‘biological’factor,thatofviraldisease?

III. The complexity of the relations between viral diseases, vectors (aphids), and pesticides

1. The influence of viral disease on the attractiveness of plants to aphids

ExperimentingwithAphis fabaeonsugarbeet,Kennedy(1951)observedapreferenceofaphidsforplantsinfectedwithmosaicvirus.Theaphid’srateofreproductionisincreasedby50%onmosaic-infectedplantscomparedtoitsfecundityonhealthyplants.Suchaprocesstakesplacenotonlyonleavesthatarestillgrowingorbecomingsenescent,butalsoonthematureleaves.Thesearemore favorable for thebioticpotentialof theaphidswhen theyshowsignsofdiseasethanwhentheyarehealthy.Inotherwords,accordingtoKennedy,‘Theillnessrenderstheentireplant,notjustthematureleaves,morefavourabletothevector.’(Fig.7.)

Suchadifferenceinbehaviourisobviouslylinkedtochangesofabiochem-ical nature, of varying degrees of significance, that occur in the leaves asa result of the disease. These changes, however, are perceptibly differentdependingonthetypeofdiseaseitself.Thus,‘mosaic’-typevirusesleadtoareductionoftheC/Nratio,whichhastheeffect,asnotedabove,ofinducinggreaterproliferationofAphis fabae.Withwhorloryellows-typeviruses,ontheotherhand,noappreciabledifferenceatallisfoundbetweenthefecun-dityofaphidsondiseasedorhealthyplants.

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What is true forone speciesof aphid isnotnecessarily true forothers,whose nutritional requirementsmay be slightly different.Myzus persicae,forinstance,atthewinglessstageofitsdevelopment,prefersleavesinfectedwithyellowing-typevirusestothosesufferingfromthemosaicor‘curly-top’viruses(Mink,1969).

Moreover, the aphid’s reproduction is also related to the severityof thedisease.Thisshowshowcloselytheinsect’sbioticpotentialislinkedtotheplant’smetabolism,Thus,onredclover(Trefolium pratense)thathasbeenexperimentallyinfectedwiththerunnerbeanvirus,yellowmosaic,MarkkulaandLaurema (1964)observed that the reproduction rateofMacrosiphum(Acyrtosiphon)pisumincreasedonplantsdisplayingonlymoderatesymp-tomsofthedisease,whileitsfecunditydecreasedinproportiontotheseverityoftheinfection.

Thesameauthorsnotethattheconcentrationoffreeaminoacidsincreasesindiseasedplants.Onoatplantsinfectedwithbarleyyellowvirus,thefecun-dityofRhopalosiphum padi(L)increasesinlinewiththeavailabilityoffreeaminoacidsintheplants.InthecaseofM. avenoe,however,reproductionrates remain the same.Thiswould appear to be due to differences in thenutritionalneedsofthetwospecies,aspointedoutabove.

Qualitative and quantitative analysis of the tobacco plant demonstratesimportantvariationsinthelevelsoffreeaminoacidsinleavesinfectedwiththeXvirus,ascomparedwithhealthyspecimens(Pojnar,1963).Aboveall,markedincreasesarerecordedinglutamicandasparticacids,lysine,threo-nine,andalanine,aswellasareductioninglycine.Suchphenomenaimplychangesatanutritionallevel,andwouldappeartoexplaintherepercussionsonthebehaviourandfecundityofaphids,accordingtotheirspecies.

Miller andCoon (1964) studied the influence of the virus itself on thebiologyofaphids.ThevirusinvolvedwasMacrosiphum granarium,feedingonbarleyinfectedwith‘yellowdwarf’virus.Thereactionsofseveralgroupsofaphidswerestudied:

• aphidsnotinfectedwithavirus,feedingonhealthyleaves;• aphidsrearedexclusivelyonvirusinfectedplants;• aphids fed for 48hours only on infected leaves and thenplacedon

healthyplants.


Inthecaseofinsectscarryingthevirus,thefindingswere:

a)anincreaseintherateofdevelopmentfromeggtoadult(aspeedingupofthedevelopmentcycleasshownbyMichel(op.cit.)withMyzuspersicaerearedontobaccotreatedwithmevinphos),

b)increasedlongevity,

c)alongerperiodofreproduction,

d)asaresult,ahigheroverallrateofmultiplication.

Accordingtotheauthors,theseresultsshowa‘biologicallyactive’interac-tionbetweenthevirusanditsvector.Webelievethatthisinteractionmustbenutritionalinnature.

Everythingwehave seen so far serves to explain themechanismof thefailureofthenumerouschemicaltreatmentsusedagainstthevectors.Infact,throughtheiractionsontheplant,thepesticidesareliable,viatrophicmeans,toincreaseaphidnumbers.Byinhibitingproteinsynthesis,theyenrichtheplant’s tissues in solublenitrogen,particularly freeaminoacids,which, inconjunctionwithreducingsugars,stimulatetheaphids’fecundity.

Thefindingswithregardtocertainchemicalpesticidesareduplicatedwithplantsinfectedbyviraldisease.Buthereaquestionarises:

IF THE APHIDS, PRESUMED TO BE VECTORS, GRAVITATETOWARDSPLANTSALREADYINFECTEDWITHVIRALDISEASESIN PREFERENCE TO HEALTHY ONES, TO WHAT EXTENT ARETHEYRESPONSIBLEFORTHEINITIALINFECTION?

Inotherwords, towhatextentareplantsthatarehealthy,orapparentlyhealthy - that is, plants conditioned in a certain way - likely to becomeinfected?ThisisthequestionthatwasalreadyraisedinChapterV,towhichwe are compelled to return.We shall respond, at least in part, by brieflyexaminingthecaseof‘parasiticcomplexes’incerealplants.

2. Physiological conditioning of cereal plants and parasitic complexes

Aswehaveseen,viraldiseasedevelopsinthecontextofso-called‘inten-sive’agriculture.Forusthistermsignifiesthedeploymentoftwo

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increasinglywidespreadtechniques:largeapplicationsofchemicalfertilisers,particularly nitrogen-based fertilisers, and (as a consequence perhaps?),ever-greateruseofchemicalpesticides,particularlyfungicides,insecticides,andherbicides.

‘Inparallel,’thereareconsiderableincreases,atfirstsightinexplicable,inbothviralandfungaldiseasesas ‘parasiticcomplexes.’Inthese,accordingtoresearcherswhohelplesslywitnessthisfloodofinfections,‘Itispracticallyimpossible to isolate the specific role of one constituent from that of theothers.’

We have already shown how pesticides, most notably herbicides, areresponsibleforparasiticoutbreaks.Herewewouldliketoraisethequestionof fertilisation, that is tosay, thenutritionof theplant.Togetherwithanypotential toxicities, aplant’snutrition isoneof theprincipal factors in itsphysiologyand,byextension,itsresistance.

First point:differencesinratesofmultiplicationinaphidsinrelationtothemethodofcultivation.

Kowalski and Visser (1983) recently studied the ‘interaction of cerealaphidswithwinterwheatinrelationtosystemsof‘alternative’agriculture.’Theylookedatthisinrelationtotheaminoacidcontentofthefoliage.

‘Conventional’ cultivation, that is the part treated with agrochemicalproducts, led to amuch larger development of the aphidMetopolophilus dirhodum (Walk) than in theareacultivated ‘organically.’Theaminoacidcontent of the leaves was also higher, particularly during July, which theresearchersascribedtoanapplicationofnitrogenatthebeginningofApril.Butotherchemicalpracticesalsoappeartohaveplayedarolesince,intheirconcludingremarks,theauthorsjudgethat‘anunderstandingoftheplant’snutrition’playsafundamentalroleinitsresistancetoinsects,andthusinanintegratedprogramofcontrol.

Parasitepopulationsweregreateronwinterwheatthathadbeenchemicallytreatedthanwherethecerealwascultivatedorganically.Thelattersufferedonlyminorinfestation,duetogreaterresistancetoaphidcolonisation.Asonefactor in thepopulationdynamicof the insect-plant interaction,KowalskiandVisser(op.cit.)stresstheimportanceoffreeaminoacids,particularlyintheirproportionsrelativetonon-proteicaminoacids.


Suchresultsconfirmtheplant-virus-aphidinteraction.

Whataretheeffectsofnitrogenfertilisers,especiallyartificialones,ontheprovocationofdeficiencies,especiallydeficienciesinmicronutrients?Herewecitethefollowingfiguresoncopperlevelsincows’milk:

• fieldstreatedwithnitrogenfertilisers:14microgrammesCuper100ml;

• fieldsnot treatedwithnitrogen fertilisers:47microgrammesCuper100ml.

Second point: Wemust also address the effects of the type of fertiliserontheprogressionofviraldiseaseandonthe levelsofaphidpopulations.HerewerelyontheresultsofthehighlyoriginalobservationsofVolk(1954)relatingtoplotstreatedwithdifferentkindsoffertilisers:potassiumchloride(ClK), sodiumchloride (ClNa),andcalciumsulphate (SO4Ca) .Thecropwaspotato.

Theplantsbearing themostaphidsgrewonsoilenrichedwithcalciumsulphate.Nevertheless, the highest percentage of disease (leaf whorl) wasfoundonchlorinatedsoils.Thistypeoffertilisationwasresponsibleforthehighestlevelofviralinfection.

The plants treated with calcium sulphate, in contrast, were relativelyhealthy,inspiteofthehighernumbersofaphidspresent.

Paradoxically, this would seem to confirm the absence of any relationbetween aphid infestation and the severity of the viral disease. In otherwords,theaphidswouldnothaveactedasvectors.However,thefertiliser’sconditioningoftheplantwouldbeimportant.,Astheauthorremarks,weshouldnotforgettheroleplayedby‘chlorinated’soils.

Wenote that chlorinehas a tendency to reduce the synthesis of aminoacids, especially proteins, and to promote the decomposition of proteins.These arepropertieswhich, at the same time, sensitise theplants to theirvariousparasites,includingviraldiseases.

Moreover, numerous chemical pesticides, especially herbicides, arechlorinatedproducts.Under such conditions,we shouldnot be surprisedateithertheirpoorselectivityorthesensitivitytheycreateinthecrop.Thisbringsusfinallytothe‘parasiticcomplexes,’thatcaneasilybeexplainedifwetakeintoaccounttheeffectsofpesticidesonthephysiologyoftheplantbeingcultivated.

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IV. Conclusions

1.Viraldiseases follow the same rule asother infections: their severity,and even their existence, depends upon different environmental factors,mediatedbytheiractiononthemetabolismoftheplant.

2. Ingeneral,and in linewithour trophobiosis theory, thecriterion forthisactionresidesinthevalueoftheratioofproteinsynthesistoproteolysis.

3. It seems that twoprincipal factors can alter plantmetabolism to thepointof‘awakening’virusesthatare‘latent,’oreveninducingtheirformationattheveryheartofthecell.Thesefactorsarethenutritionoftheplantandthepossibletoxiceffectoffertilisersorpesticidesonit.

4. By ignoring such effects of pesticides, and aiming only at chemicaldestructionofthevectors(chieflyaphids),thedeploymentofpesticideinter-ventionhasledtofailure.Thereareatleasttworeasonsforthis:

• ithasnotyetbeenproventhatanyparticularaphidisresponsibleforthetransmissionofavirus,somethingthatseemstodependaboveallonthephysiologicalstateoftheplant;

• after an initial fleeting impact on the pest, pesticides canmake theplantmoresusceptibletobothviraldiseasesandaphids,throughtheireffectsonthephysiologyoftheplant.

Here,asforotherparasites,itturnsoutthatsensiblepestcontrolagainstviral diseases resides in the adequate conditioning of the plant, either byachievinganoptimumrateofproteinsynthesis,thankstobalancedfertilis-ationandcorrectionofdeficiencies,orbyavoidingtoxiceffects,whichseemtoariseespeciallyfromtheuncontrolleduseofchemical(nitrogenousandchlorinated)pesticides.Wewillgivesomeexamplesinthelastpartofthisbook.

131 The Impacts of Grafting on the Scion’s Resistance

Chapter 7

The Impacts of Grafting on the Scion’s resistance

I. Objectives and Consequences of Grafting

In Chapters IV and V, we have already touched on grafting and thesusceptibilityofthesciontowarddisease.Wenowreturntothis,inordertolookattheprobleminamoregeneralformandtoestablishanideaofthephenomenaattheonsetofsusceptibilityorresistanceofthescion.

To recall the justification for this technique of grafting; it is necessaryfor thepreservationof thevarietyandfor itsrapidreproduction. Astockadaptedtothesoilallowscultivationofavarietythatwouldnototherwisebepossible.Thisisthecase,forexample,forpeachtreesonsoilsthatarenota priorisuitableforthem.

Moreover,while it very often happens that grafting sensitises the sciontowardvariousparasites,itcanalsoleadtoresistance.Forexample,graftingagainsttheviraldiseaseSharka.

Finally, grafting canbe a last resort against apathogenic agent throughaprocessof ‘tolerance,’ ifnotdestructionordissuasion.Thiswasthecase,celebratedinagronomy,withtheregenerationofFrenchvineyardsbytheuseofAmericanrootstockstostaveoffPhylloxera.

The physiology of the stock-scion composite

Graftingcreatesaneworganism.Itisa‘composite’or,toputitbetter,a‘chimaera.’Itspropertiesareneitherthoseoftherootstockplantnorthoseofthescion,butaredistinctivetotheneworganismthathasbeencreated.

However, the scion supplies the roots with carbohydrates and othersubstancesdevelopedintheleaves,whiletherootsabstractmineralelementssuchasK,Ca,Mg,S,andmicronutrientsfromthesoil.

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Moreover,thephysiologyofthecompositeprovestobedependentontwoselections:

• attheleveloftheroots,chieflythroughtheuptakeofcationicelements;• atthejointitself.

Butdiseaseoccursmostlyonthescion.ThisisthecasewiththefamousapplestockscollectedatEastMalling, inBritain.ThevarietyM1displaysgreatsensitivitytotheenvironmentandshowshighneedforpotassium.AtthesametimeitencouragesthedevelopmentofOidium,scab,andcankerattacksonbranchesoftheCoxvariety.Numerousstocks,besides,areinfectedwithviruses.

Infact,wearefacedonceagainwitha‘parasiticcomplex.’Weshouldnotbesurprised,thentoencounteroneongraftedvines.Wenowintend,tolookattherepercussionsofgraftingonthegrapevine,atechniquethathasbeenputtouseonahugescale.

II. The severity of diseases of the vineyard in relation to its reconstruction through grafting

One of the first diseases of the grapevine for which grafting has beenheld responsible was Botrytis cinerea. This is also in resurgence, as wehaveseenabove,becauseoftheuseofcertainchemicalfungicides,suchasdithiocarbamates.

‘GreyrothasalwaysexistedinFrenchvineyardswithvaryingdegreesofseverity.Butduring thepast twenty years, since the replacementof thewholecountry’svineyardsbymeansofgrafting, ithasbecomefrequentand extensive. It is only since then thatwehave begun toworry aboutfightingthisdisease.’

WiththeselinesPerrierdelaBathe,ateacherattheSaintesAgriculturalCollege,begananarticleongreyrotinAugust1904inRevuedeViticulture.Certain typesofvine, suchas ‘folleblanche’areespeciallyaffected.Whengrafted,whichmakesitmore‘vigorous,’thisvinecanhardlybecultivatedanylongerduetoitsexcessivesusceptibilitytoBotrytis.


Escaorapoplexy,causedbyattacksofthefungusStereumhirsutum,hasalsobecomefarmorevirulentsincethemassgraftingofFrenchvineyards.Whilethisparasitehadpreviouslybeenconsideredasapathogenicagentinoldervines, itnowbegan toattackyoungstock.Thishypersensitivitywasattributedbysometoprematureageingoftherootstockandtoproductionoftannin.Clearlythereisaconnectionbetweenattacksofescaandthealtera-tionofthescion’smetabolismbythegraftingprocess.

There isalsogoodreason toask towhatextentgraftingmayhavebeenresponsibleforthesevereoutbreaksofmildewfrom1880to1885,afewyearsafterthere-establishmentofFrance’svineyards.IntheRoussillonregion,forexample,thefirstrootstockswereplantedin1883,andwithinsixyearstheentirestockofvineshadprettymuchbeenreplaced.Butmildewraged-withthehelpoftheclimate-in1885,1887,and1889,withlossesreachinguptohalftheyearlyaverageharvest.

Of course, somewill say these aremerely coincidences.But since 1873MaximeCornu-whonameisforeverlinkedtothatofPhylloxera -hadwarnedagainst thedangersof introducingAmericanvines intoFrancebecause intheirownhomelandtheyhadbeenattackedbyPeronospora viticola.

WastheAmericanrootstockabletopassontothescionsits‘susceptibility’todisease,includingmildew,aswellasBotrytisandesca(nottomentiontheviraldiseases, towhichwe shall return later)?. Iswhatweencounterheresimplya‘parasiticcomplex’suchaswehavealreadyseenincropsasvariedascerealsandfruittrees?

We shall perhaps understand this mechanism better by looking at thephysiology ofRiparia, the rootstockmost widely used for re-constitutingvineyards,andstillamongstthemostwidelyusedtoday.

III. The physiology of Vitis riparia and of certain ‘composites’ of Riparia and scion

TheAmericanvineVitis ripariawas, fromthe start, themostpopular,withmillionsstillgrowingintheSouthofFrance[1984].OneofRiparia’scharacteristicsistogivecertainvinesabushyshapesothatinFrenchonesaysofthesevinesthatthey‘se riparient’(‘becomebushy’).

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Thisbushiness is found inotherplants,particularly theapple tree. It iscalled ‘witch’sbroomsticks.’Thesemalformationsdonothaveaparasiticalorigin.Theyarecausedbyacalciumdeficiency,whichinturnmaybecausedbyaborondeficiency.

Thisproblem,alsoknowninapplesas‘proliferation’diseasedoesnotrelyondiseasedapplesforitsdissemination.Itdependsprimarilyonthesoilanditscomposition(Bovey,1971).However,levelsofinfectionarehigherwithcertainrootstockvarieties,suchasE.M.XI,thanwithothers,suchasE.M.XII.Thisclearlyconfirmstheinfluenceoftherootstockontheplant’snutri-tion,andwithittheresistanceofthegraftedplanttothistypeofinfection.

InvinesgraftedontoAmericanvines,variouskindsofdeficiencieshaveemerged.For instance, graftedMerlot shows a cleardeficiency inmagne-sium.Inthebranchesoftheplant, theK/Mgratiovariesaccordingtotherootstock(Table9)(Duval-Raffin,1971).

Table 9: Variations in the K/Mg ratio of Merlot according to the nature of the root system.

Root system Mg (mg/kg dry weight) K/Mg ratio

Ungrafted merlotMerlot/riparia x berlandieri SO 4Merlot/riparia x rupestris 3309Merlot/vitis riparia

2110 7651009 912

5.3914.2711.2817.09

InthecaseofgraftedMerlot,therefore,wefindaMgdeficiency,particu-larlywhengraftedontoVitis ripariawherethevalueoftheK/Mgratioisthehighest.Duval-Raffin(op.cit.)concludes: ‘Graftinginsoilpoorinmagne-siumincreasestheriskofdeficiencyofthiselementinMerlot.’

ThesameauthorshowedthatRipariaisalsopoorincalcium.Thiscouldcertainly explain the ‘riparisation’ of certainplants, particularly in certainsoils.Suchdeficiencies,especiallyofmagnesiumandcalcium,arealsofoundin fruit trees: walnut (Gagnaire and Vallier, 1968), citrus (Wallace et al.,1953),peach(GrosclaudeandHuguet,1981),etc.BlancAicardandBrossier(1962)considerthatthestockdeterminesthecationicbalanceintheplant,particularlytheratioofdivalentionstomonovalentions.Aswehaveseenabove,thisratiointurngovernstheplant’sphysiology,especiallythelevelofproteinsynthesis,ortheratioofproteinsynthesistoproteolysis.Thisisacriterionoftheplant’sreceptivenesstoitsparasites.


All the same, the effects of grafting on the scion’s metabolism are notconfinedtotheelementsN,K,Ca,andMg.Thiswouldnotbeso,apriori,becausewealreadyknowtherelationsbetweenthemajorelementsandthemicronutrients,suchasB,Zn,Mn,Mo,andIetc.Infact,variousstudieshaveshown the influenceof the rootstockon themicronutrients.Forexample,studiescarriedoutbyLabanskasandBitters(1975)oncitrustrees,establishthevariationsofKandCa,aswellasofCl,B,Cu,andFe.Thisalsoincludessulphur.

Carlesetal.(1966)haveshownthatontwodifferenttypesofgraftedvine(18,815and12,375Seyve-Villard),graftingleadstopronounceddifferencesinminerallevels,especiallycopper.Inungraftedvines,levelsofcopperaresignificantlyhigherthaningraftedones.Mnlevelsalsovary,beingnotablyheightenedbyRipariaXRupestris3309.

Deficiencies, viral and other diseases

Wehavealsoreceivedastartlingdemonstrationofagraft-induceddefi-ciency through the appearance of chlorosis. It has been affirmed that ingrapevines, chlorosismakes its appearancewith grafting. In non-graftedvines,infact,chlorosisremainedsubduedanddidnotpreventthecultiva-tionofafflictedvarieties,even inconditionswhichpromotechlorosis (forexample,vineyardsintheCognacregion).Thevarietieswerethesameastheonesusednowadays-merlot,cabernet,sauvignon,semillion,etc.-butweretoleranttochlorosis.

This‘tolerance’couldariseeitherfromtheplants’lowironrequirements,or fromthepropertiesof their roots,allowing themtoeasilydissolveandabsorbtheironpresentinthesoil.

After the reconstruction of the French vineyards using American root-stocks,certainstock-scioncombinationswerefoundtobemuchmoresensi-tivetochlorosisthanvarietiescultivatedontheirownroots.Thisisbecausetheironrequirementsoftheaerialsystemofthecombinationwerenolongersatisfiedby thepoorabilityof certain root rootstocks systems tomobiliseironfromthesoil.

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Accordingtoourconceptoftrophobiosis,thegrapevine’ssusceptibilitytochlorosisthroughirondeficiencycouldalsoproducesusceptibilitytootherdiseases,particularlymildew.IsthisperhapshowRiparia,whichalsocausesdeficiencies of calcium and perhaps boron, could transmit susceptibilitytowardmildewtothescion?ItiscertainlyinterestingtonotethatMillardethimselfpointedoutthattreatmentsbasedonironsulphate,whenaddedtolime,gaveexcellentresults in treatmentsagainstmildew.1Thiswould leadus toadmit thatachemical’seffectivenesscomes frominternalactionandthrough correction of deficiencies. This would constitute a revolution inthetherapyfordiseases,aswehavepointedoutinourpreviouswork.Wewillnowlookattherelationofviraldiseasestothetechniqueofgraftingthegrapevine.

Whataretherelationsbetweengraftingand‘receptivity’forviraldiseasesandotherinfections?By‘grafting’wemeanthemodificationsofabiochem-icalnaturethatarecausedinthegraftitself.

These same deficiencies, notably P and Ca, occur not only with Vitis riparia,butalsowithotherrootstocksof thegrapevine.HalmiandBovay(1972)showedthatRiparia X Rupestris3309-awidely-usedrootstock,oftenusedasareferencepoint-leadsinthechasselasgrapevinetonutritionhighinNandK,averageinMg,andpoorinPandCa.

When European varieties are grafted onto the same 3309 rootstock,Mikeladze(1965)wasabletoshowthat:

• theprocessofsynthesisintherootsoftherootstocksslowsdown,thequantityofaminoacidsdecreasingincorrelationwithanaccumulationofsugarsthatarenotusedinthetransformationsoftheKrebscycle;

• intheleavesofthescionweobserveanaccumulationofaminoacidsduetotheslowingdownoftheirconversionintoproteins(andperhapsintoother importantcompounds)requiredfortheplant’scontinuedgrowthandthecirculationofions.

Inshort,thephysiologyofthewholegraftedplant,particularlythescion,reveals inhibition of protein synthesis. This reveals a metabolism with aheightenedsusceptibilitytovariouspathogenicagents.

Anexperimentaldemonstrationofthis‘susceptibility’isprovidedbythedifferenceintherateofmultiplicationofmites(or‘redspiders’)ontheMerlotvine,accordingtothenatureoftherootstock.


Thebioticpotentialofthe‘redspider’Panonychus ulmi,feedingoffMerlotwithVitis riparia as the stock, is on average 70%higher than forMerlotgraftedonBerlandierixRiparia420A(fig.8Aand8B)(Carlesetal.,1972).

Analysesofthefoliageseemtoshowclearlythatthesedifferencesinthemite’slongevityandfecundityhavetheirorigininhigherlevelsofaminoandamidenitrogeninredmerlotgraftedontoVitis riparia(fig8C).

A physiological state inwhich proteolysis predominateswould seem tofavouracertain‘laziness’inproteinsynthesis,itselfinducedbycertaindefi-cienciessuchasthosealreadyshowninthecaseofcalciumandiron(tosaynothingofotherpossibledeficienciesstillunstudied,suchasboron).Thisconfirmswhatwehaveseenabove,thatdeficienciesareclearlytheoriginofviraldiseasesthat,likeotherdiseases,arerampantinplantsrichinsolublenitrogen.

Wecansee,therefore,whytherewereatfirstsuchdramaticoutbreaksofdiseases of the grapevine after the reconstitution of the French vineyardsbymassgrafting-forinstance,thedevelopmentofBotrytis-thatcapturedthe attention of the researchers. (We note in passing that the process of‘sensitising’thevinebytherootstockisparalleltothatbroughtaboutbytheuse of the dithiocarbamates zineb,maneb and propineb against grey rot)(Chaboussouetal.,1966).

Manifestations of viral diseases are less striking, but no less real.TheirspreadhasoftenbeenlinkedtoPhylloxera,frequentlyaccusedofbeingthevector-forexample,inthecaseofinfectiousdegeneration.OnthissubjectBranas remained sceptical, only noting that therewas a link between theinvasionofPhylloxeraandthespreadofthevirus.

However,itseemsthatanimportantfactorhasbeenforgotten.Ashigh-lightedbyCiferri,thisistheroleplayedbytheplantitself,servingasnutritionalhosttobothparasites.EverythingthatwassaidbeforeaboutthephysiologyofscionsonAmericanrootstocksshowsthatifphylloxeraisresponsibleforthespreadofviraldiseasesofthegrapevine,thisisonlyatasecondarylevel.ItoccursbecausetheEuropeanvine,tomakeit‘tolerant,’hasbeengraftedontoAmericanplants.Thelatter,asaresultofthedeficienciesandinhibitionofproteinsynthesisthattheyinduce,makethescionsusceptibletovirusesandotherdiseases,particularlytoinfectiousdegeneration.

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Fig.8: Effects of the nature of the grapevine stock on the fecundity of aphids raised on Merlot rouge grafts.

Differences in fecundity on the Merlot rouge vine, according to whether this vine is grafted onto Vitis riparia or onto Berlandiera x Riparia 410A.N.B. - The bars O, I, II, III, IV indicate the periods when the aphids were raised, at intervals from mid-May to 20 July.This graph does not show the results of the breeding period H V (20 July - 15 August) or H VI (5 September - 10 October), where the results are the inverse of those of the first four periods. (See the following diagram.)


Weknow,moreover,thatVuittenezhasshownthatthenematodeXiphinemaindextransmitsinfectiousdegeneration.Previousconsiderations,however,thatrankthevine’sphysiologicalstateasbeingofthehighestimportancefortheplant’s‘receptiveness’todisease,reducetheroleofvectorstoasecondarylevel.

Wemustinfactdistinguishclearlybetween‘resistance’and‘receptiveness’toPhylloxerawithout,however,underestimatingtheinterestofagronomyingrafting,whichpermitsthecultivationofgrapevinesin‘phylloxeric’soils.Inthisregard,Maillet(1957)observedthat,ingeneral,

‘theplantswiththegreatestreputationfortheir‘resistance’toPhylloxera(Vitis riparia, Vitis rupestris)weretheoneswiththemostabundantandmost thriving Phylloxera populations, with a maximum of ovariolesleadingtoamaximumofeggclutches.’

Wehavealreadyseenthatthe‘biochemical’and‘trophic’reasonforthisisthesameasforthesusceptibilityofgraftedvinestothe‘parasiticcomplex’madeupofBotrytis,mildew,viraldiseases,Phylloxera,andmites.Asimilarcomplexisfoundintheappletree,aspointedoutearlier,wheretherootstockMI.isconsideredas‘weak’or‘weakening’forthescion.

Inshort, inregardtograpevines,Maillet(op.cit.)couldjustifiablystatethat ‘graftinghasbeenandalwayswillremainonlyapalliative;Phylloxerastillremainsunconquered.’Suchacritiqueofgraftingisallthemorejustified,aswehaveshown,becausegraftingcanpromoteacomplexofdiseases.

Letusmakeitclear,however,thatsucheffectsstemfromrepercussionsoftherootstocksemployedatthetimeofthere-constructionofthevineyards.Thingscouldbequitedifferentwithnewrootstocks,suchastheonerecentlydevelopedbytheINRAatBordeaux.Thistype,fercal,hasneitherV. riparianorV. rupestrisinitsancestry,anditsgeneticcharacteristicsareBerlandieri x Colombardno.1x333EM.Wenoteaboveallthatthisvarietyhasshownitself far superior in its resistance tochlorosis.Wecould thereforeassumethat itwouldhave little orno irondeficiency,whichmightmake ismoreresistanttovariousparasites.

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Fig.8B: Evolution, over the course of a season, of the relations of fecundity of P. ulmi on Merlot rouge, as affected by two types of stock: Riparia and 420A.

N.B. - The reader will note (due to the biochemical evolution of the grapevine as it approaches senescence) the inversion of results, from the beginning of mid-July, for the last two groups of aphids.


Fig.8C: Fecundity of Panonychus ulmi in relation to the ratio: amine N and amide N / N (NH4), in grapevine leaves for the aphid populations II, III, IV, and VI.

N.B. - Apart from Merlot rouge grafted onto 410 A and Riparia, the populations VI and VI involve a third type of foliage - that of Merlot rouge on its own roots, hence the initial F (free).

The reader will note the very significant inversion of the results for the groups V (mid-July to mid-August) and VI (early September-early October), with respect to foliage F. The latter, resistant to aphids until mid-July, becomes susceptible at this stage as a result of senescence: the breakdown of proteins and the consequent elevation of amino acid levels.

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IV. Rootstock-induced resistance in the scion

Asweshallnowshow,certaingraftingtechniquespermittransmissiontothescionofbetterresistancetodiseases,particularlytoviraldiseases.

Sutic (1975), who attempted to stimulate plants’ resistance throughgrafting,founditwaspossibletocombatvariousdiseases(‘neckrot’incitrustrees (Phytophthora parasitica) and apple trees (Phytophthora cactorum),androotrotinpeachtrees(Phytophthora cinamoxi))bygraftingontoappro-priaterootstocks.

Likewise, rootstocks that seem ‘resistant’ to theTrusteesvirus inappletreesareatleast‘tolerant’to‘latent’viruses,eventoPhytophthora.

WehavealreadyseenwithregardtoPhylloxera,thatwhatisinvolvedisatolerance.Thisallowsthevinetosurviveandtoreproduce,butalsosensitisesittodiseases,includingviralonessuchasinfectiousdegeneration.Thisisthecase,atleast,withtherootstockshabituallyuseduptonow.

Isitpossibletofindrootstockscapableofinducingagenuine‘resistance’inthescion,orrather,immunitytoitsprincipalparasites?Wehaveseenthatthereisaneedtodistinguishclearlybetweenthepresenceofthepathogenandthedamagecausedby‘disease’.Ifdamageisavoidedthroughatechniquesuchasgrafting,thenwehaveamethodofcontroleveniftheparasitetoacertainextentsurvives.

ThereisoneexampleofthedeploymentofrootstocksagainstthediseaseTristeza in citrus trees, identified for the first time in 1955 in theMeyerlemon. Frezal did not find any symptoms of the disease on the AntilleseOlimettier(Citrus aurantifolia Christ.Mexicanvariety)eventhoughin1967thesesametreeswere foundtobecarriersof theTristezavirus(especiallytheOwariSatsumas).Inotherwords,thephysiologyofthescion,modifiedbythespecialnatureoftherootstock,preventedmultiplicationofthevirus.

If thiscanbeachievedwithavirus, thesamecouldbeachievedagainsteveryotherinfection,forinstanceamycoplasma,acryptogamicdisease,orevenaninsectpest.If,aswehaveshownabove,certainrootstocksthroughtheir metabolic effects promote the establishment of veritable ‘parasiticcomplexes,’theycancreateresistancetotheappletreewoollyaphid.


ThusSoulard(1952)suggeststhattherootstock’simmunityistransmittedtothescion.Inthecaseofthewoollyaphid,‘thefewfeeblecolonieswhichappearonitgrowmiserablyandareradicallydestroyedbythefirstgenera-tionsofitsparasite,Aphelinus mali,beforehavingcausedanydamage.’

Infact,‘graftingasaprocedureforvegetativeprotection’wassuccessfullyusedbySutic(op.cit.)tocontrolSharkadisease.InthiscaseinfectedPozegacabuds were grafted onto the crown of theMalevezka plum. Malevezka isparticularlyresistanttothedisease,andthesymptomsofSharkadisappearedafter three to four years from the shoots coming from the infected buds.Symptomsdidnotre-appearlater,eitherintheleavesorinthefruitoftheshoots.

Analogoustechniqueshaveproducedsimilarresults.Sutic(op.cit.)reportsthatinYugoslaviaandRomaniastudieshaveconfirmedtheactiveroleplayedbyPrunus spinosa var. dasyphyllainthe‘vegetativeprotection’ofplumtreesinfectedwithSharka.Thesamephenomenonoccurswithapricottrees.

Suchresultsshouldbecomparedtothoseobtainedthroughaffranchisse-mentwhich, according toBouché-Thomas (1948), protects the apple treefromcanker,woollyaphidsandcochineals.Theyalsoraisethequestionofthenatureofthebiochemical factorscausingthis immunityor ‘resistance.’Onthissubject,theresultsobtainedbyDoVale(1972)can,itseems,giveususefulinformation.

DoVale(op.cit.)carriedoutresearchonthebiochemicaleffectsinducedbyvariousrootstocksgraftedtoLisbonlemon.Heconcludedthat:

‘The combinations giving good results produced low levels of solublesugarsinspringleaves,closetothelevelsfoundinnon-graftedtrees.Atthe endof the season, the sugarswere significantlyhigher in the leavesofthescionshavingproducedthebestresults,resultsasgoodasthoseintheirnon-graftedcounterparts.Whereperformancewasmediocre,highquantitiesoftotalsugarswerefoundinthespringleaves.’

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Notes1 Usingtheformula:4kgofironsulphateto20kgoflime.Cf.InternationalCongresson

Phylloxera,Bordeaux,1881.

All thiswould appear to confirmwhatwehave seen abovewith regardto metabolic differences between grafted and un-grafted trees, primarilymanifestedbydeficiencies.Inotherwords,thelowlevelofproteinsynthesisingraftedtreesyieldsonlymediocreresults.

These results are similar to other grafting successes in relation to viraldiseases, such as those obtained by Morvan and Castelain (1972) incontrollingchloroticwhorlintheapricottreebygraftingPrunus spinosa.

It would undoubtedly be interesting to be able to standardise plantmetabolismbyabiochemicalcriterionwhoseimportancetothemetabolicprocesses isknown. Forexample, thiscould involve the linkbetweenthecationsK+Na/Ca+MgorK/Caasafirstapproximationof thevalueofarootstock.Thiswouldalsoshowthepotentialresistancethatitwouldbelikelytotransmittothescion.

Fromanotherperspective,itwouldalsoallowthepredictionofpotentialdeficienciesinmicronutrients.

V. Grafting and the quality of the product

Sincegraftingaffectsthescion’sphysiology,itmustalsoaffectthequalityof the harvest. This question has not escaped the attention of viticulturespecialists.Thequalityofwineis linkedtothesugar level inthegrapesatacertainstageinthevine’svegetativecycle.Sincethesugarcycleandsugarlevelsdependonthenatureoftherootstock,thisalsocontrolstherhythmof growth.An earlyhaltingof the vegetative stage, allowing the grapes tomaturewellandthusyieldingagoodqualitywine,isbestachievedingeneralwithaweakrootstock.ThisisthecasewithVitis riparia,arootstocklikelytopromotedisease,nottomentionspreadofPhylloxeraintheroots.

Sohowcanwereconcilewinequalitywiththeplant’sresistance?Coulddiseasecontrolresideincorrectionofdeficienciesthroughtreatmentsofanutritionalkind?Thisiswhatweshallexamineinthelastpartofthiswork.

145 State of Health in Relation to the Method of Cultivation

PART THREE

Agriculture Techniques and the Health of Crops

‘Howthedevilcanallthesediseases,alreadycatastrophicenough,black-mailcerealcropsinsuchafantastic,ceaselessway?Whatsortofcursehasbeenplacedonthesefields?Istherenowayoutofthisinfernalspiral?’

(PublicitybookletofPROCIDApesticidecompany,1980.)

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Chapter 8

State of Health in Relation to the Method of Cultivation

I. ‘Intensive’ cultivation of cereal crops and the xxplosion of so-called ‘diseases of progress’

1. Parasite intensification: proliferation, not ‘resistance’ to pesticides

Wewillnowtakeupthedisturbingquestionsthatfarmersthemselvesareraisingabout thecausesof theproliferationofparasitesaftertreatmentbycertainpesticides.

Itisonlyinthelastfifteenyears[to1984]-thatwehaveseensuchaspreadofdiseaseincerealcrops.Wemustalsorememberthatuntilrecentlymanyofthesediseaseswereunknown,ortheireffectsinsignificant.Thisisthecase,forexample,withFusariosisandSeptoriosis.

Other diseases such as take-all in cereals and crown and sheath rot inrice (Gaeumannomyces graminis) and Rhizoctonia are also spreadingbeyondthenorm.‘Barleyisoftensubjecttoanattackbyaparasiticcomplex(Rhynchosporiose, Oidium,take-all)inwhichitispracticallyimpossibletoisolatethespecificroleofanyoneoftheconstituentparts’(Harranger,1982).

Hereagainweencounter‘parasiticcomplexes’,whoseoriginwecanassessonlywhenwetakethephysiologyofthehostplantintoaccount.

ThereisalsothedrasticspreadofHelminthosporiosis,withtheappearanceof new species, and also of viral diseases such asDwarf yellow in barley(whichalsodevelopsinothercereals).

A researcher at INRAconcluded that thesedevelopments ‘appear tobelinkedtotheincreasingacreagedevotedtothecultivationofthiscrop,andtotheintensificationofagriculture.’Thisresearcherdoesnotgointofurtherdetail.

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Even the pesticide company whose discouraging statement we quotedat thestartof thissectionbearswitness to thisuncertaintywhen it states:‘In fact, endemic diseases constitute a veritable baseline disease complexwhichmustalwaysbetakenintoaccount....Ifcertaindiseaseshavesorapidlybecomethissevere,theremustbeotheraggravatingfactorsnotaccountedforsimplybynaturalandclimaticconditions’(Procidapesticidecompany).

Inourviewwhatisinvolvedisan increase in susceptibility ofthecerealsthroughwhatisusuallycalledthe‘intensification’ofagriculture.Thistermcoverstwoessentialprocesses:

• increased fertilisation, in particular the massive use of nitrogenfertilisers.

• theequallymassiveuseofchemicalpesticides,especiallyherbicides,andfungicides.

A researcher at ENSAIA in Nancy was able to establish that themainfactorsinthedevelopmentof‘brownstains’(Helminthosporiosis)were:

• earlyanddensesowing;• nitrogenousfertilisers;• fungicidetreatmentsappliedduringthecourseofvegetativegrowth.

It should come as no surprise that a non-persistent chemical acting onthesurfaceasafungicidecanalsoalterthecereal’sphysiology,andthusitssusceptibilitytoitsvariousparasites.Moreover,someresearchersarescep-ticalabouttheefficacyofsystemicfungicidesforcerealdiseases(Parmentier,1979).

A similar indirect influencevia thephysiologyof theplant in this case,cerealsledtoabeliefthatthepathogenicagent(variousfungi)haddevelopedresistancetothefungicides.InthecaseofPietinverse,someresearchersspeakoftheexistenceofvarieties‘resistant’toBMC(Benomyl,methylthiophanate,carbendazine).But we have seen, particularly with respect to the grapevine, how much credit we should give these alleged ‘resistances.’ What is involved is a proliferation of the specific parasite through stimulation of its biotic potential, based on a nutritional effect.

Whatisthemechanismofthissusceptibility?Hereherbicides apparentlycome intoplay,according towhatweknowfromvariousstudies, someofwhichhavebeenanalysedinthecourseofthechaptersonviraldiseases.


Onlythrougheffectsonthephysiologyofthecerealcouldsuchdevelop-mentsofviraldiseasesbeunleashed.Referencesinthebibliographywillbackthisup.

TheworkofAltmanandCampbellisparticularlyimpressive(1977).Thisgivesageneralsurveyoftheroleofherbicidesinthedevelopmentofplantdisease.Theauthorsrecapitulatethemanycasesofdiseasebroughtaboutbypesticideuse:

1) Inhibitionofplant growthby applicationof aherbicide leads to anincrease in susceptibility to disease: for example, beetroot treated withcycloate,acarbamate.Asforthemechanism,AltmanandCampbell(op. cit.)suggestthatinfactoneofthecausesofdevelopmentofdiseasecouldbeanincreaseinthenutritionalsubstancesavailabletothepathogen.

2) Furthermore,treatmentofsoilswithcycloateproducesmuchhigherlevelsofglucoseandmineralsaltsintheplantsthatgrowthere.Thesenutri-tionalsubstancesareexudedthroughtheleaves.Theyleadtosusceptibilitytopathogenicfungithatfeedontheleaves,byaneffectthatisnutritionalinnature.Thisisaninhibitionofproteinsynthesis,whichenrichesthetissuesinsolublesubstancesthatmaketheplantsusceptible.Thechiefsubstancesareaminoacidsandreducingsugars.

Somepesticidecompaniesseemtobeawareofthesemajordisadvantages,andalsoofthosethatcouldresultfromfurtherexpansionofthemarketinherbicides.Ratherthanrenouncingthem,theyappeartobetryingtocounterthedisadvantagesbybringingout ‘antidotes,’ substances thatwould allowaherbicidetobeselectiveinrelationtothecroptobeweeded.Evenifthisdevelopment should by chance prove successful, it will not address theimpactofherbicides’onthelifeandcompositionofthesoil,whichweshalldiscussfurtheron.

2. The effects of atrazine and 2.4D on the development of various parasites.

McKenzieet al.(1968)showedthatwithcornresistantto ‘dwarfmosaicvirus’(MDMV),severityofthesymptomsincreaseswiththedosageofatra-zine.Withadoseof20ppmofatrazineappliedtothesoil,symptomsincreasebyupto100%.(Fig.5).

Theseresultswereconfirmedsubsequently(McKenzieet al.,1970).Theyalsoshowthatatrazineprofoundlyaltersthebiochemicalcompositionofthefoliartissues,particularlyinP,K,Ca,Fe,Cu,B,Al,SrandZn.

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Inaddition,Gramlich(1965)showedthattreatmentinthefieldledtoamuchhigherpercentageofnitrogen in cornand sorghumhalepense thaninthecontrols.Thiswasthecasewithweak dosesofatrazine.Thisexplainstheincreasedsusceptibilitytoparasitesbroughtaboutbythischemical.Thisbecomesevenmoreapparentwhenoneconsidersthat,withgrasses,simazineincreasestheeffectivenessofatrazine.Thisincreasestheriskofproblemsincropsthroughthepersistenceofthischemical,alongwithitsnegativeeffectsonproteinsynthesis.Theseproblemsbecomemoreseverenotonlythroughphytotoxicitybutalsothroughsusceptibility,bymeansofmechanismsthatarenowunderdiscussion.

AltmanandCampbell(op. cit.)studiedtheeffectsofsimazineonwheat.Theyfoundthat,incomparisonwithcontrols,itincreasednitrogenlevelsby30%,slightlyincreasedthelevelsoftheaminoacidsthreonineandvaline,andveryclearlyincreasedthelevelsofasparagine.Asweshallseeconfirmedlater, this amino acid is particularly ‘effective’ in nutritionally promotingthebiologicalpotentialandproliferationofparasites,especiallypathogenicfungi.

From their studies of the literature, moreover, Altman and Campbellconclude that the inhibition of protein synthesis by these herbicides canexplain many of their harmful effects. Carbamate herbicides can in factinhibitutilisationofaminoacidsbyvulnerablespecies.Theseauthorsalsonotethatthesechemicalshaveastructureincommonwithproteins–thatis,CO-NH.Theyconclude:

‘Since1945,numerousreportstellofincreasedlossesthroughinsectandpathogen attack, despite ever greater efforts at pest control.While it isdifficulttocalculatetowhatextenttheseincreasesareduetothebiochem-icalandecologicalimpactsofherbicideuse,herbicideshavebeenblamedinnumerouscasesforcausingproblemsofparasitisminthetreatedplants.’

Thislossinplantsof ‘resistance’toinsectsanddiseasecanbeexplainedthroughtheavailabilityofimprovednutritionfortheparasites.Thisoccursthroughinhibitionofproteinsynthesis,aswellasthroughenrichmentofthetissueswithsolublesubstances(aminoacidsandreducingsugars).


Inconcludingtheirstudy,AltmanandCampbellpointout:‘Itispossiblethat the use of herbicides can alter the susceptibility of the plant beingcultivated.’

Theexaminationwehavemadeof simazine whichalso leads toprolif-erationof leafhoppersonmaize - is also relevant, aswe shallnowsee, totheartificialhormone2,4D.OkaandPimental (1976) in fact showed thattreatingmaizewith2,4Dleadsto:

• proliferationofmaizeaphids,inproportiontothedoseused;• swarmsofmaizePyralidæ(Ostrinia nubilalis).

Thestatisticsarethefollowing(Table10).

Table 10: Effects of 2,4D on aphid and pyralidæ populations on maize

Doses of 2-4 D Aphids (in September) Pyralidæ - % of maize attacked

Controls0.14 kg/ha0.55 kg/ha (standard dose)

6181,3881,679

16%24%28%

Theseresultscamefromstudiescarriedoutin1973;andrepeatedin1974with similar results.As to theaverageweightofpyralidæ pupaeonmaizeplants, treated respectivelywithdosesof5.2and80ppmof2,4D, thiswasfound to be significantly higher than on the controls. This fact seems toconfirmthenutritionaladvantageforpyralesofmaizetreatedinthisway.

Throughothertests,furthermore,OkaandPimentel(op. cit.)alsoshowedthatthesusceptibilityofmaizetoHelminthosphoriosiswasincreasedbyuseof 2,4D.Thisappearstoconfirmtheideaofa‘parasiticcomplex,’inwhichnoxiousinsects,pathogenicfungi,bacteria,andevenvirusescanco-existonthesameplant.

The results of Oka and Pimentel explain the observations made byAdams andDrew (1965)with aphids. These showed that proliferation ofRhopalosiphum padiandMacrosiphum avenaeonoatsandbarleywasasso-ciatedwiththeapplicationof2,4D.Onecanthereforeimaginethedifficultyof interpreting resultswhen an aphicide is applied simultaneouslywith aherbicide,torestrainfromtheoutsetthedevelopmentofaphidpopulations.

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However,whenevertheherbicideisappliedonitsown,weseethataphidpopulations,which vary fromyear to year, are alwayshigher thanon thecontrols:108%higherin1962,and205%higherin1963.Theauthorsputtheseincreasesdowntothenegativeeffectsoftheherbicidesonladybirds.Buttherearegroundsforsurmisingindirectrepercussions,througheffectsonthephysiologyofthespecificcereal.

Itshouldcomeasnosurpriseif,byananalogousprocess,thePyrethrum-type insecticides used against maize Pyralidæ should also make aphidsproliferate.Basedonwhatwehavealreadyseen,theseincreasesinPyralidæwouldappeartobelinkedtoherbicideuse,particularlyinthecentralandParisianbasinregionsofFrance.Significantly, it is theagriculturalexpertsthemselveswhoendupwonderingaboutsuch‘abnormal’proliferationandwhatextentitmightbelinkedtoanincreasedsusceptibilityofmaize,dueto‘amodificationofthephysiologyoftheplantswhichwouldmakethemmoreappetising’(Agri-Sept,17thApril,1981).

Suchcloseinquiryisencouraging.Infact,itshowsthatthese‘biologicalimbalances’cannotbeexplainedbythe(realor,moreoften,alleged)destruc-tionofnaturalpredators.Anentirelydifferentexplanationiscalledfor.

To sumup, theseproliferationsof parasites on cereal crops result froman alteration of the plants’metabolism by the use of chemical pesticides.Mostoftentheseareherbicides,butinsecticidesandfungicidescanalsobeinvolved.Sotoocanchemicalfertilisers.

ApartfromPyralidæandaphids,otherpestscanproliferateoncerealcropsforsimilarreasons.Thisisparticularlytrueofnematodes.Whileinthepast,diseases caused by worms have been neither numerous nor serious, fourtypesofnematodesthatdamagecerealcropshaverecentlybeenrecorded.AnematodespecialistatINRAwasledtoacknowledge,‘Theevolutionofagri-culturalmethodshasencouragedtheappearanceofspeciesnotpreviouslysuspectedorintroducedfromelsewhere.’(Ritter,1981).

It is strange that,amongst these ‘modifications’ inagriculturalmethods,thereisnomentionofeitherthenewandintensiveuseofherbicidesortheintensifieduseoffertilisation,particularlyofnitrogenfertilisers.)However,aswasdemonstratedlongago:‘Ontheoatplant,2,4Dstimulatesthedevel-opmentofDitylenchus dipsacibymodifyingthebiochemistryoftheplant,rendering itmore suitable for the parasite’s diet’ (Wester, 1967; Rambier,1978).


Variousfungicidescauseproliferationofnematodes,particularlyonstraw-berriesandonions.

Ithasbeenshownthat levelsofaminoacidsandamides intherootsofnematodeinfectedplantsarealwayshigher(from17%to316%)thanthoseinhealthyplants(HanksandFeldman,1963).Thisseemstoclearlyexplainthe‘integration’ofnematodesinthe‘parasiticcomplexes’recordedsinceabout1969orso-inotherwords,sincetheintensiveuseofherbicidesbegan.

Italsoseemslikelythattheeffectsoffungicidesandthetypeoffertiliserintervene in such a process. These aremainly nitrogen fertilisers, heavilyusedtoincreaseyield.Thereasonsarealwaysthesame:enrichmentofthetissuesinsolublenitrogen.Thussomeexperimentscanleadtoconclusionslikethis:

‘Fertilisers, particularly those over-rich in nitrogen, lead to an increaseindamagecausedbyparasites.Thus,inresearchonwheatcarriedoutin1972bytheI.T.C.F.,inthenorthernhalfofFrance,theuseofafertilisercontaining240unitsofNperhectareledtoadecreaseinyieldof250kg/ha,duetoincreaseddamagecausedbyparasites.’(BTI,‘Protectionofcrophealthbycerealrotation,’1975).

Parmentier(1979)repeatedlywarnedofthedangersposedtocerealcrops,especially byOidium, through the indiscriminate application of nitrogenfertilisers.

3. The ‘secondary’ effects of fungicides on cereal crops

Weshallnowanalyse somespecial studiesof theeffectsofBenomyloncerealcrops.

Fungicidestooarebeingcalledinquestion.Asusualwhenanypesticideprovestobeineffective,thecauseissaidtobeapossible‘resistance’bythepathogentothespecificfungicide.However,whatwehaveseenoftherela-tionship‘cerealherbicide’,or‘nitrogenfertiliserparasite’,shouldleadustoexaminetheissuefromtheperspective‘plantparasite,’accordingtothe‘conditioning’ofthecereal.

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InGreatBritain, the two strains strains of eyespot (Pseudocercosporella Herpotrichoides)thataresaidtoberesistanttobenzimidazolesarefoundinparcelsofcropstreatedwithBenomylandcarbendazine.Thesetreatmentsmaywellhavemadethecerealsusceptibletoeyespot.Buttheotherpossi-bilityisthattheplanthasalreadybeenmademoresusceptibletoattackbypreviousapplicationsofeitherherbicidesorfertilisershighinnitrogen.Thiswould render fungicide treatments ineffective.A scrutinyof theeffectsofBenomylappearstoconfirmthishypothesis.

According to an eminent plant pathologist, in the 1960s this fungicidepromised ‘to fulfill everyone’sdreamsof a successful treatment’ (Ponchet,1979).Ithasnowbeenthesubjectofanindepthstudyofitseffectsoncerealcrops(Poulain,1975).Hereisabriefanalysisoftheoutcome.Thisresearch,whichwasthesubjectofadegreethesis,wascarriedoutbothinthelabora-toryandinthefield.

Inthelaboratory,Benomyldidnotalwaysactasafungicide.In vitro,thepresenceofBenomyldidnotpreventthegerminationofFusarium roseumspores,evenatrelativelyhighconcentrations(10ppm).Benomylevenstim-ulatedgrowthofthemyceliumatdosesonlyslightlylowerthanthosethatinhibititsgrowthtotally.

Inasimilarway,BenomylshowsfavourableeffectsonSeptoria nodorum.Thisoccursontwolevels:

• itleadstoanearlierappearanceofpycnides.

• itincreasesthepercentageofcoloniesformingpyrenoids.

ThreestrainsthatwereintheprocessofdegeneratingwereregeneratedbytheapplicationofBenomyl.

It is not therefore surprising to find that three Benomyl sprays appliedonryegrowinginthefieldledtoamajorincreaseinattacksbyRhizoctonia solani.Thisshowsclearlythatwhatisinvolvedisproliferationcausedbythefungicide,andnota‘resistance’ofthefungustowardthechemical.

ThefieldresultsobtainedbyPoulain(op. cit.)arenolessinterestingandthought-provoking.Firstofall,theyconfirmthepositiveeffectsofnitrogenfertilisersondiseases.IntestsonCapitolewheat,diseasespreadsslowlyintheperiodbeforeJune25,atthebeginningofvegetativegrowth,butexplodessoonafterwards,whetherornottheplanthasbeentreatedwiththefungi-cides. ‘Thefungicidetreatmentdoesnotstopthespreadofthediseasebutmerelydelaysitsprogressionfortwotothreedays’.


To recap: despite this ‘qualifier,’ Benomyl has not proven itself to be a‘fungicide,’ as far as Septoriosis is concerned. In confirmation of what wepreviouslydiscussed,oneofthereasonsforthisfailurecouldbethephysi-ological‘conditioning’ofthecereal,mainlybyfertilisers.Poulainnotesthatnitrogenrichfertiliser(220U)appliedtohardywheat‘hasprobablypreventedthe fungicidal treatments from acting normally.’ The author adds: ‘Aloneamongthediseasesoftheroots,Rhizoctoniashowedamajorspreadwhich the treatments appeared to promote.Asingleapplicationofthefungicide,infact,leadseithertoagreaternumberofinfectedplantsortoanaggravationofthedisease’.

Proliferationoccurs in thesecircumstancesbecausepesticidesmake thecerealssusceptibletothesedisorders.Themechanismbehindthiscouldbethefollowing:

Toxiceffects (ofherbicideorfungicide)Malnutrition (excessofnitrogenfertiliser)

Metabolicproblem (inhibitionofproteinsynthesis) (triggeringofdeficiencies)

Sensitisation (tofungaldisease) (soluble (toanimalpests) substances)

alterationofcellnucleusonsetofavirus

One last indicationof theprofoundand long-termeffects thatBenomylhasonplantphysiology:asPoulainnotes, ‘Ineverycase, thegerminationpotentialofbatchesofplantstreatedwithafungicideduringthevegetativephasewaslowerthanthatofuntreatedbatches.’

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4. Herbicides and weeds

Chemicalcontrolhasnotbeenable towin thebattleagainstweedsanymorethanthebattleagainstplantdiseases.Heretoo,theso-calledproblemof ‘resistance’arises.Everythingwehavesofarsaidchallengesthevalidityofthisterm,particularlyiftheso-called‘secondary’effectsofherbicidesinsomewaystimulatethegrowthofplantsthatareconsideredharmful.

Beyond their direct effects on plants during application,herbicides can modify the life of the soil.Throughtheirharmfuleffectonmicroorganisms,theyarecapableofaffectingtheprocessesofnitrificationandtheactivityofenzymessuchasphosphorylaseanddehydrogenase.Thiscanleadtomalnu-tritionoftheplant,resultinginthesusceptibilitythatwedescribedabove.McClurg and Bergman (1972) were able to show that various herbicidetreatments can lower calcium levels in plants, resulting inmajor damage.Theysimultaneouslyreducebothresistanceandcropyield.

Wecanalsodrawaparallelbetweentheeffectsofherbicidesandthoseofnitrogenfertilisers.Asmentionedabove,acertaindoseoffertilisercanblocktraceelementssuchascopper1withalltheconsequencesofsuchadeficiencysuchaseffectsontheplant’sphysiologicalstateanditsresistancetoparasiticattack.

Ithasbeenpointedoutthatpesticidesthatcontainnitrogen–practicallyallchemicalpesticides-arecations.TheycanreplacecationssuchasCa,Mg,andZnfromtheexchangecomplex.Thesameis trueofchlorine.Huguetshowed clearly that repeated applications of nitrogen fertilisers result ininhibitionofboroninthecherrytree.

The same process seems to explain the disappearance of calcium afterprolongedtreatmentwithNPK(BetaegheandCottenie,1973).

We should also point out the reduction in phosphorous levels in soiltreatedwithMCPAandmalathion(Vicario,1972).

Wecouldjustifiablyaskwhethersuchdisturbancesinthesoilmightexplainfailuresintheuseofherbicides.Thesedisturbancesresulteitherfromcertainfertilisers(mainlynitrogenones),orfromnitrogenousandchlorinatedpesti-cides(herbicides,fungicides,insecticides).DeficienciesinPandlowlevelsofCaandMgpromotethedevelopmentofdicotyledons.Recentlytherehasbeenaspreadofself-sowinggrasses:forinstance,


foxtailandwildoats,aswellasdicotyledonssuchaschamomiles,knotgrass,and speedwell. The spread has been ascribed, erroneously, to ‘resistance.’(Barralis,1978).Mightthisnotrepresentananalogousphenomenon,duetodisruptionsincationicelements?

Here,oncemore,wearedealingwithproliferationduetochangesinthenutritional environment offered to the self-propagating plant. This couldexplainhowsomeinsecticidesusedagainstmaize Pyralidæ (Ostrinia nubi-lalis),whichinevitablyfallonthesoil,caninfluencethenatureoftheflora.Onestudy,forexample,notesthestimulationofvariousspeciesof‘weeds’inmaizefieldstreatedwithdiazinonagainst Pyralidæ (GojkoA.Pivar,1967).Astheauthorconcludesinhisarticle:‘Theseresultsshowthenecessityofcontinuous and systematic study of the appearance and spread of weeds,afterpesticideshavebeenappliedtoprotectcultivatedplants.’

Asonecropexpertrecentlystated,withregardtoweedcontrolinmaizecultivation:‘Thecontinualuseofconcentrateddosesofatrazinecreatesnewproblems.What isnoticeable is the ever increasing difficulty in eradicating summer grasses, but without the appearance of true resistance’(Morin,1981).

Other examples include the failure of triazines against knotgrass. InVilliers-BonneuxinYonne,south-eastofParis,farmerswerehavingdifficul-tieseliminatingknotgrass(Polygonumlapathifolium)whichhadchloroplastsresistanttoatrazine,apre-emergenceherbicide.Maizeandcornhadbeengrown in rotationon these fields since 1964.The ‘resistance’ of the knot-grass appearedafterfiveor six applicationsof atrazine (with the formula,C8H14ClN5).Accordingtonotedresearchers,however,thespectacularspreadoftheknotgrass‘pointstotheconclusionthatnumerousresistantplantswereselectedfromtheveryfirsttreatmentsandthenproliferatedgreatly,profitingby the selective advantage the atrazinegave them’ (Darmency,Compoint,andGasquez,1981).

However, it seems rather unlikely that selection could havemanifesteditselffromtheveryfirsttreatments.Selectionisnormallyalengthyprocess.The authors seem, quite right to be astonished. Yet, it does not seem sounlikelythatafterfiveorsixyearsoftreatmentwithsimazine,thischemicalwouldbeabletomodifythesoilinsuchawayastopromotethegrowthandproliferationofknotgrass.Besides,itdoesnotseemtobemerechancesince,ascertainobservershavenoted.

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‘Inagriculturalpractice,onespeaksof‘resistance’toatrazinewhenoneishelpingwiththemassivesurveyofweedsaftertheapplicationofatrazine’(Morin,1981).

Suchamannerofspeakingsuggeststheexistenceofanimmediateprocessofproliferation,not just a laterdifficultywith eradicationafter a seriesofinterventionswithherbicides.

Theseremarksseemtoconfirmthat,asinthecaseofthe‘biologicalimbal-ances’resultingfromtreatingfoliagewithpesticides,twoessentiallydifferentprocessesarecommonlyconfused:genuineproliferationandallegedresist-ancetoapesticide,whichismuchmorerare.

Itwouldalsoappeartoexplainwhyitisineffectivetotrytoovercomethis‘resistance’toherbicidesbyincreasingthedosage.Suchapracticecanonlyendby increasingproliferation.These indirect repercussionsofherbicidesconfirm the position of those who think it ‘is totally mistaken to releasecomplexmoleculesintonature,inacomplexenvironment,withouthavingatleastsketchedoutawayofcontrollingthem’(BoucheandFayolle,1981).

II. The state of health of cereals using traditional techniques: ‘organic agriculture’

A publication from IRAAB (Institute for the Research and ApplicationofOrganicAgriculture) lookedatnine farms thatwerepracticingorganicfarming- inotherwords,withoutusingartificialpesticidesandfertilisers.Onsomeofthesefarms,where‘classic’or‘chemical’agriculturehadprevi-ouslybeenpractised,thefarmerswerefacedwiththespreadofweedswhichsystematicuseofchemicalherbicideshadnotbeenabletoprevent.Perhaps,aswesawabove,theherbicidesevenencouragedtheweeds(particularlyinthecaseofcouchgrass,thistles,wildoats,andfoxtail).

In contrast, re-conversion to ’organic’ led to the disappearance of theseweeds,particularlywildoatsandsorrelinsandysoils.

Referencesinvolvingimprovementofthesoilinthisrespectarefoundinfourfarmsoutoftheninereviewed.Whataccountsforthedisappearanceoftheweeds?


Ifweexaminethenewgrowingconditionsthatthefarmersadopted,wefindthattheyfallintotwocategories:

• Onfarmnumbertwo,wheretherehadpreviouslybeentwoweed-killerapplications,twotreatmentsagainstfungaldisease,andonetreatmentagainstaphids,bothwildoatsandsorrelhavedisappeared.

• Italsoseemsclearthatotherpracticeshelpagreatdeal.Firstly,somedeep ploughing has led to the eradication of couch grass. Greateremphasisonleguminousplants(orcompanionplanting:leguminousplusgrainplants)allowsforthecleaningofthesoilanditsenrichmentin organic nitrogen and calcium. This effect is the inverse of whathappenswithfertilisationusingsyntheticchemicalsorwiththeutili-sationofchemicalpesticides(especiallyfungicidesandherbicides).

Moreover,accordingtothefarmersthemselves, thishasnotonlysolvedtheproblemofweedinfestation.Ithasalso:

• shownthathaltingpesticidetreatments(aswesawregardingaphids)seemstoleadtoanexcellentstateofhealthinthecrop.

• led to better health in livestock, by the elimination of septicaemia,mastitis,etc.(Itevenleadstotheeliminationofticks-apointwhichitwouldbeunreasonable toneglect, if this shows theexistenceofacertainstateof‘physiologicalresistance’inanimals.)

• demonstrated, finally, important energy savings. The study showedthat ‘organic agricultural methods for cereal production (maize,wheat,barley)consumearoundtwotothreetimeslessenergythandoconventionalagriculturalmethods.’

Suchresultscouldthereforebeconsideredasaconfirmationoftheharmfuleffectsofsyntheticchemicalsthroughtheirdualactionontheplant:atoxiceffectbydirectactionatthemomentoftreatment,andaratherpronouncedalterationofthenutritionmechanismsofthecerealcrop.Theresultsthere-fore seem to confirmour theoryof trophobiosis, particularly through thetechniquesofthistraditionalagriculture:stimulationoftheresistancebothofplantsand,vianutrition,oftheanimals(includinghumans)whofeedonthem.Allthiscomestogetherinimprovement of the nutritive value of food, according to the nature and level of protein synthesis.Thiscomprisesavastandengrossingsubjectofresearchforphysiologistsandothernutritionists,onethathasonlypartiallybeenattemptedbefore(Schuphan,1974).

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A question of yield: 5,000 kilograms per hectare a reasonable objective or a dangerous myth?

Yieldsof5,000kilogramsperhectarehavebeenrecordedoncertainsites,particularlyinFrance.Butisthisareasonableaiminallagriculturalsitua-tions?Aprimaryobstacletoincreasingyields,onwhicheveryoneisagreed,isclimate.Mildandwetwinters,forinstance,leadtoplantsputtingouttoomanysuckers,resultinginanumberofinferiorearsofgrain.Ontheotherhand,adroughtduringthemonthofJunecanbeequallydamaging.However,there have beenhardly any publicationswarning farmers against reducedyieldsbroughtaboutby these farmingerrors:namely,unbalanced fertilis-ation and pesticide intervention (herbicides, insecticides, and fungicides.Progressisequatedwithchemicalcontrol.Andtheseriousrepercussionsofpesticidesonthe‘health’ofplants,especiallycerealcrops,canbemaskedbyotherfactors.Itisthefarmersthemselvesandtheircommonsensethatcanhelpusanswerthequestionsposedabove.

Obviously,ayieldof5,000kg/hacanbeachievedthrough‘intensive’agri-culture,withhighlevelsofnitrogenfertiliserandrepeateduseofherbicide.But such techniques render the cereal susceptible to diseases, especiallyviral diseases, confirmed by the need to extend fungicide and insecticidetreatments.

Onthissubject,the‘LetterstotheEditor’incorporatenewspaperssuchasAgri-septhavemuchtoteachus,ifweonlyreadbetweenthelines.Oneletterrunsasfollows:

‘Toomany farmsof theLoiret havebeenblindedby the cerealmirage.TheLoiretisaheterogeneousdepartementwherewefindtherichBeauceregionproducing4,000kg/haofwheatalongsidelessproductiveregionssuchasOrleanais,Sologne,Giennois,andBerry.From1970to1974,goodharvestsandhighpricesencouragedalargenumberoffarmerstoploughuptheirpasturesandselltheirlivestockinordertobuypowerfultractors.

‘Thegoodyearswereoftenfollowedbybadones.Thesatisfactoryyieldsof 19721973 (2,000 to 2,250 kg) dropped from 1974 onwards. At thepresenttime,ifwetaketheaverageofthelastsevenyears,theyieldisonly1,650,1,750kg.Thisisclearlyinsufficient,becauseithardlycoverscosts’(Agrisept,May2,1981).’


Sowhatbroughtaboutthisdropinyields?Is itnotduetooutbreaksofdisease, the inevitable corollaryof ‘intensification’of agriculture? Inotherwords: excessive nitrogen fertiliser, plus the harmful effects of herbicidesandthenfungicides?Whensomeonespokeof5,000kg/ha,afarmerintheToulouseregionlaughedandsaid:‘Thewheatgotattackedbydwarfyellow,andtheaveragewasonly3,050to3,100kilogramsahectare.’

Another farmer said: ‘5,000 kilograms? I don’t think that’s possible orsensible.Thepointisn’tproducingmore,butproducingatthelowestcost.Inadroughtyear,whenyou’veputonyourtreatmentsandputdownnitrogen,therearenightswhenyoudon’tsleeptoowell.’

Thesefarmershadnotyethadthechancetodrawaconnectionbetweentheirfarmingmethodsandtheoutbreakofwhatare(hypocritically?)called‘diseasesofprogress.’Thesediseasesnaturallyneedtobetreatedwithmorechemicals,thusfurtherincreasingthecostofgrowingthecrop,inaviciouscircle. However, since it is becoming clear that one cannot control viraldiseases‘chemically,’mightthisnotleadpeopletoaskabouttherealcause,orevenbegintoblamethepesticidesthemselves?

By way of contrast, the example of the results of traditional (organic)agriculturehasshownusthatcertainagriculturaltechniques,particularlyabalancedfertilisation,canstimulatetheresistanceofaplanttoitsparasites.Ricegrowingoffersafurtherexamplewhenwestudyitfromthisperspective.

III. Rice growing: health problems and the results of a balanced fertilisation

1. Rice parasites

Theprincipalenemiesofriceinclude:

a) afungaldisease,‘blast,’causedbyPiricularia oryzae (riceblast).Thisafflictiondoesmajordamage,especiallyinIndiaandBrazil;

b) abacterialdiseasecausedbyXanthomonas oryzae.Everyyear, thisaccountsforthirtypercentofthelossinricecropsinJapanandSouthEastAsia;

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c) variousinsects,chieflythefollowing:• aleafhopper,Nilaparvata lugens,orBrownricehopper.Itsattackslead

to a blackening, and thendyingoffof the rice.Chemical pesticideshave not been able to address this. According toNew Scientist, thecauseoftheseoutbreaksof‘hopperburn,’whichwasneversoharmfulinthepast, is ‘certainfundamentalchangesinagriculturalpractices.’Wewilltakeupthispointlateron.

Amongtheothernoxiousinsects,weshouldalsomention:• theclassic‘borer’,orChilo suppressalis,amicrolepidopteran;• thericestemborer,Tryporyza incertulas;• thewhorlmaggot,Hydrellia sesakii;• the‘greenleafhopper’,Nephotettix virescens,\oneoftheCicadellidae;• the‘leafroller’,Cnaphalocrosis medinalis.

Tocompletethelist,weshouldmentionthericeweevil,Sitophilus oryzoe.Itstollisgrowing,likethatofotherinsects,withthegrowthinuseofnitrog-enousfertilisers.

2. Some harmful effects of herbicides on the resistance of rice to its parasites

IshiiandHirano(1963)wereperhapsthefirsttowarnagainsttheharmfuleffectsof2,4D,whenusedtocontrolweedsinriceplantations.Thissynthetichormone causes more intense attacks by the borer Chilo suppressalis.Accordingtotheseresearchers,proliferationofthisinsectismorerapidinricestemstreatedwith2,4D, duetohigherlevelsofnitrogeninthetreatedplants(+25%)comparedtocontrols.

Forthesamereason,treatingriceseedwithaldrinincreasesthenumberoflarvaeofthericewaterweevil,Lissorphoptrus oryzophilus(Bowling,1963).

Themechanismofthissensitisingofricearisesfromanincreaseinsolublenitrogeninthericetissues,asIshiiandHirano(op. cit.)haveshown.Thisprocessisidentical,weshallnowsee,tothatcausedbynitrogenfertilisationwhenitisnotsufficientlybalancedwithpotassium.

However,pesticidesandespeciallyherbicidesmaybemoretoblamethanmisguidedfertilisationforthedevelopmentofvariousparasites,duetotheinhibitionofproteinsynthesiscausedbythesechemicals.


It hasbeen shown that rice, alongwithother species of aquaticplants,absorbsandconcentrateschlorinatedproducts(pesticidesandpolychloro-phenols)intheaquaticenvironmentsoftheCamargue.Theseplantsabsorbandconcentrate thechemicals (alphaandgammaHCH,DDTandPCB).Measuredindryweight,thelevelsofconcentrationinrelationtolevelsinthewatervaryfrom16-foldto20,000-fold,dependingonthespeciesandthechemical(Vaquer,1973).Itisthereforenotsurprisingthatsuchconcentra-tionscauseacutechangesinthemetabolismofthetreatedplant(inthiscase,rice).

2,4D is obviously not the only herbicide used in rice growing.Wewillsingleout,forexample:• fenopropor2,4,5TPwiththeformulaC9H7O2Cl3,usedaftergermina-

tionatthe34leafstage,whensuckersarebeingputout;• propanil(C9H9NOCl2)appliedasapre-emergent;• and finally, nonchlorinated molinate (C9H17NO4S) derived from

carbamicacid.Ithasbeenshownthatthenitrogencontentofplantstreatedwithcarbamateswhetherherbicidesorinsecticidesincreasescomparedtothatofthecontrols,andthattheyoftenbecomesuscep-tibletovariousparasites.

Astochlorinatedproducts,itiswellknownthattheyreduceaminoacidsynthesisandpromoteproteindecomposition.Becauseoftheseproperties,the chemicals can often act as herbicides. However, the same phytotoxicpropertiesaffectthecerealcropbeingweeded.Nodoubtthiseffectismuchlessmarked,butsuchaninhibitionofproteinsynthesiscanrenderthecropsusceptibletoawholerangeofparasites,includingviraldiseases.

Inregardspecificallytorice,TrolldenierandZehler(1976)foundthatalargenumberofpathogenicorganismsdepend,fortheirnutritionandgrowth,on the soluble constituentsof cells such as sugars and amino acids. (ThisconfirmstheviewofDufrenoyandourownconceptoftrophobiosis.)Suchsubstancesarefoundinhighconcentrationsinplantscontainingabundantnitrogen,particularlythosethataredeficientinpotassium.ThisexplainstheharmfuleffectofahighN/Kratioandtoomuchnitrogen-richfertiliseronaplant’slevelofresistance.Wewillnowseethisconfirmedinthecaseofrice.

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3. Fertilisation and the resistance of rice to its parasites

A. Harmful effects of nitrogen chemical fertilisers.

Having seen how herbicides make rice susceptible to its parasites, weshouldnot be surprised by the effects of nitrogen fertilisers. Eden (1953)showsthatthedamagecausedbythericeweevilSitophilus oryzoeincreasesinproportiontothequantityofnitrogeninthefertiliser.WehaveseenthatthesamemechanismwasatworkintheproliferationofthericeborerChilo suppressalis,causedby2,4-D.

However, theeffectsofnitrogen fertilisersareperhapsmost clearlyandspectacularlyseenwith ‘blast’,orPiricularia oryzae.Throughexperimentsusingammoniumsulphate,Sridhar(1975)wasabletoestablishthatahighlevel of soluble nitrogen in the leaves of rice promotes the spread of thedisease.Piricularia oryzae uses various aminoacids as sourcesof carbon.In plants fertilised with these chemicals, glutamine and asparagine levelsincrease.Sridharconcludes,therefore,thathighconcentrationsofnitrogenin thehostprovide thepre-requisites for thedevelopmentof theparasiticfungus.

Thisexcessofsolublenitrogenintheplanttissuecanresultinpartfroma dis-equilibriumwith the other elements, inhibiting the condensation oftheaminoacids into insolubleproteinswhichareofnonutritionaluse tothevariousparasiticorganisms.Thisisoftenthecasewithpotassiumdefi-ciency.WeshallseethatriceconformstothegenerallawoftheimportanceoftheN/Kbalanceforaplant’slevelofproteinsynthesis,andthereforeitsresistance.

B. Beneficial effects of potassium fertilisers on the resistance of rice to its various parasites.

Clearly,theapplicationoffertiliserdoesnotcallforththesamereactionsfromallstrainsofrice.Ranga,ReddyandSridhar(1975)wereabletoshowthat,dependingonthevarietyofrice,identicalapplicationsofpotassiumdidnothavethesameoutcomewithrespecttothebacterialdiseasecausedbyXanthomonas oryzae.WhilenoimprovementinresistancewasinfactnotedinthehighlysensitivevarietyT(N)I,theapplicationofpotassiumhaltedthediseasemarkedlyinthelesssensitivevarietyIR8.


However,confirmingthegeneralrule,theleavesofthesensitivevarietyT(N)Ishowedhigherlevelsofphenol,reducingandnonreducingsugars,andaminoacids,thanthoseinthelesssensitivevarietyIR8.

The results clearly show that the phenol content has no link with theprocessofresistance(accordingtotheideaofapossibleantagonisticeffect).It is the presence of soluble nutritional substances - reducing sugars andaminoacids-thatmakesricesusceptibletothedisease.

In the end, according to these authors, it is insufficient application ofpotassium that promotes the buildup of these substances in the leaves ofthese two varieties, by comparisonwith plants providedwith a sufficientamountofthiselement.

Thebeneficial influenceofpotassium fertilisers inpromoting resistancetofungaldiseasesisalsoshownbytheresistanceofricetovariousnoxiousinsects.This factemergesparticularly fromrecent researchcarriedoutbyVaithilingam(1982)onresistanceofricetovariousinsects,broughtaboutbypotassiumfertiliser.

Thankstobothfieldandlaboratorytrialsthatinvolvednumerousanalysesofleaves,Vaithilingam(op. cit.)establishedthatpotassiumleadstoanotabledegreeofresistancetoaseriesofinsectsharmfultorice,whenappliedasafertilisertoplants.Theseinsectsare:• thebrownplanthopperorBPH(Nilaparvata lugens).This result is

allthemoreinteresting,sincechemicalcontrolofthisinsectistotallyineffective.

• thegreenleafhopper(Nephotettix virescens),aCicadellidae.• theleafhopper,Cnaphalocrocis medinalis.• the rice stemborer (Tryporyza incertulas),whosenumbers are also

significantlyloweredinricefertilisedwithpotash.• finally,Hydrellia sesakii.

The author concludes‘Against the five principal insects observed, amaximumdoseof150kgofK2Operacreprovedsoeffectivethatnotasingleapplicationofinsecticidewasneeded.’

ForVaithilingam,thisresistanceprocessresultsfromtheplant’sincreasedutilisationofaminoacids for thebuildupofproteins.On theotherhand,withadeficiencyofpotassium, there isabuildupofvariousaminoacidssuchasvaline,alanine,asparticacid,glutamicacid,arginine,etc.

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Thisiswhy,astheauthorpointsoutwithreferencetonitrogen,onemustbecareful todistinguishclearlybetweenproteinandnonproteinnitrogen.Resistanceislinkedtoanabsenceofammoniumnitrogeninthetissues.

Potassium fertilisation should also, it appears, increase resistance todiseases such asPiricularia.Wewill discuss this disease later, in relationto the roleof the trace elements.Other cationic elements alsoplaya role.Primavesietal.(1972)notethattheratioK/Cais7.6inhealthyriceplants,ascomparedto2.9inricesufferingfromPiricularia.

Thebeneficialresultsshouldalsoshowupinrelationtoviralandbacterialdiseases.Thisisaresult,aswehaveseenabove,ofthecommonmechanismat the root of the ‘parasitic complexes’which stem froma lackof proteinsynthesis.However,accordingtocurrentknowledge,achievinganoptimumofproteinsynthesisdependsbothonthenatureoftheavailablepotassiumandonitsbalance(aswereportedabove)withtheothermetabolicelements,chieflythetraceelements.

In this respect we should note that, according to Xie JeanChang et al.(1982),absorptionofpotassiumbyriceiscorrelatedmorecloselywithpotas-siumthatisabsorbedslowlythanwithpotassiumthatiseasilyavailable.Thisbringsupanimportantpoint:inintensivegrowthconditionswithhighdosesofnitrogenandphosphate,potassiumlevelsarefartoolowforricetogrowproperly.

Is this a general phenomenon? It could explain the harmful effects ofexcessivenitrogen,whicharelinkedtoappearancesofdeficiencycausedbyunbalancedNPKfertilisation.AlthoughfertilisershighinN,P,andKleadintheshorttermtohigheryields,theybringlossesofnutritionalelementsthatarenotreplaced.Severalstudiesofdeficienciesinthetraceelements,Ca,Mg,andSconfirmthisratio.

AsBussler(1982)notes:‘Aswellasdeficiency-relateddiseaseswithvisiblesymptoms,latentdeficienciesareattractingmoreandmoreattention.Withmoreintensiveuseoffertilisers,thebalanceofallthenutritionalelementsbecomesmoreimportant,especiallyinlightsoils.’

Some symptoms of deficiencies in nutritive elements have in fact beenobserved, particularly in poorly drained soils. Analyses have shown thatalthoughthesesoilscontainedhighlevelsoforganicmatter,theywerepoorininterchangeableK,aswellasinavailablePandZn.


Thisexplainswhysuch‘organic’soilscanbetransformedintoproductivericefieldsbyaddingcertaintraceelements,forinstanceCu,Mo,andZn,toanNPKfertilisation.(Quidez,1978)

C. The influence of trace elements on the resistance of rice to its parasites.

Thepreceding analysis dealtwithdifferent studies of resistance in rice,accordingtothetypeoffertilisation.Itshowsthatthebalancebetweennutri-tionalelementsplaysamajorrole,relatedtothe levelofproteinsynthesiscausedbythisbalanceintheplant.Ifthetraceelements,throughtheiractiononenzymes,areadetermining factor inproteinsynthesis,weshouldalsoconsidertheirbalancewiththemajorelementssuchasN,P,K,andCa.

Theseconsiderations,relatedsofarmostlytoresistancetoattacksbyinsectpests,seemtoapplyjustaswelltodiseases.AsShigeyasuAkai(1962)notedinregardtoriceHelminthosporiosis: ‘Untilnow,studiesoftherelationshipbetweenpotassiumandplantdiseaseshasnotshedmuchlightontheinflu-enceofpotassiumsupplementationonthemechanismofdiseases.’

However,theauthor’sresearchconcerningpotassium,basedonhydropon-icallyraisedplants,showedthattheproportionoflargeHelminthosporiosisspots on the leaves was lowest when treated with ‘excess potassium.’ Incontrast, the proportion was highest with the ‘potassium deficient’ and‘nitrogendeficient’treatments.

Moreover,thegerminationrateofconidiainfungalparasiteswaslowestaftertreatmentwith‘excesspotassium,’whileitwashighestafterthe‘deficientin nitrogen’ treatment. This correlateswith the composition of the liquidexudatefromthericeleaves.Thisliquidcontainsvariousaminoacidssuchasglutamicacid,asparticacid,andleucin.AccordingtoShigeyasu,‘Itseemsthatthegerminationrateofthesporesisalmostproportionaltothequantityoffreeaminoacidscontainedintheleaves,Themoretheleveloffreeaminoacidsisraised,the more the germination rate of the spores is raised.Astothelevelofpotassiumintheleaves,thishaslittleinfluence.’

Thiswouldconfirmtheindirectroleofpotassium,byitsactiononproteinsynthesisandbyitsmobilitywithintheplant.TheK/Nratioalsoplaysarolehere.Accordingtosomeresearchers,applicationofnitrogenexclusivelyintheformofammoniahasanantagonisticeffectonthericepaddy’sabsorp-tionofpotassium.Thepresentwriterhasalsoobservedalowerpotassiumlevelintheleavesofriceplantsinplotswithexcessivenitrogen.

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AK/Mgantagonismhasalsobeennoted.AsShigeyasu(op. cit.)commentsconcerning this, ‘The influence of Mg and P should probably be takenintoaccount inplotswithanunbalancedK/Nratio, for examplewithanexcessofnitrogen.’Theauthoreventuallyconcludesthatthe development of Helminthosporiosis marks on potassiumdeficient rice is caused by an inhibi-tion of synthesis of proteins due to free amino acids.However,heconcludesfromtheseresultsthatpotassiummustbeconsiderednotonitsownbutinrelationshipwiththeotherelements.Thecriterionforahighrateofresist-ance,hestates,isahighlevelofproteinsynthesisand,conversely,alowleveloffreeaminoacids.

With regard to trace elements, Shigeyasu (op. cit.) notes that suscepti-bility toHelminthosporiosis decreaseswith the applicationof iodine, zinc,ormanganese.Thisalsohasafavourableeffectonvegetativedevelopment,whichconfirmsthebeneficialeffectsofthesetraceelementsontheproteinsynthesisprocess,whichoccursthroughtheiractionontheenzymes.

Conversely, the same author states that susceptibility to the parasiteincreaseswhenthereisalackofmagnesium,anexcessofpotassium,oranadditionof cobalt.Theauthor concludes: ‘The effectofpotassiumon theresistanceofricetoHelminthosporiosiscannotbeassessedpurelyfromtheangleofpotassium.’ThisconclusionisclearlythesamethatwecandrawfromthestudiesofPrimavesiet al.(1972)inrelationtoresistancetoPiriculariainrice,towhichwenowturn.

Tosumupbrieflytheimportantworkoftheseresearchers,wenotethatthey referfirstof all to certain fundamental lawsofbiology,primarily thefollowing:

• An abundant NPK fertilisation promotes a plant’s susceptibility todisease.

• A certainbalancebetween the elements ismore important for cropproductionthananover-abundantfertilisation.

• Thereisaverydelicatebalancebetweenmacro-elementsandmicroe-lements,justasbetweenbasesandacids.

• Themostdelicatebalanceistheonebetweennitrogenandcopper.


Thebasicreasonwhythis lastpointseemedimportanttotheauthorsisthatthediseasePiriculariaintheirviewarisesfromanutritionalimbalance:anexcessofnitrogen,whichitselfstemsfromadeficiencyincopper.

TheK/Nratioisalsoimportanthere,aswithotherplants.Excessivelevelsofnitrogenleadtodeficienciesinpotassium.Primavesiet al.(op. cit.)pointouthowanexcessofnitrogencausesafundamentalmodificationofthemetabo-lismofrice,leadingtoenrichmentofthetissuesandexudatesinaminoacids.Theresultissusceptibilityto‘blast’,aswellastoHelminthosporiosisAfurtherresultistheineffectivenessoffungicidesasstressedbyvariousresearchers.ThisispointedoutparticularlybySallaberryRibeiro(1970),byPrimavesiet al.,andbySanchezNeira(1970),allofwhomconcludebyrecommendingwellbalancedlimingasaneffectivepreventivemeasure.

TheresultsofthetrialsbyPrimavesiet al.(op. cit.)areasfollows:

• Thereisahigh,statisticallysignificantcorrelationbetweenyieldandlevelsofCaandMg.

• pHhasanimpactontheseverityofthedisease:healthyricegrowsinwaterwithapHbetween5.4and5.8;ricesufferingfromPiriculariagrowsinwaterwithapHlevelvaryingbetween6.8and7.9.

• Nitrogen-richfertilisersincreasethesusceptibilityofrice,whilepotas-siumlowersit.

• Maximumyieldisobtainedwithanaveragelevelofpotassium.• Higherlevelsofpotassiumarerecordedinhealthyrice(0.891%)than

inricesufferingfromPiricularia(0.739%).

Relations between the elements vary greatly depending onwhether thericeishealthyorsufferingfromthedisease.Wegiveatableshowingsomeoftheratiosbetweenvariousnutritionalelementsinriceplants,accordingtotheirconditionofresistance(Table11).

Table11clearlyshowsthatdiseasedricesuffersfromamarkeddeficiencyinMg,K,Mn,andCu.Itisworthrecallingthatwefoundsomedeficienciesof this typeproduced symptoms similar to those caused in grapevinesbyviraldisease.Thisledustoraisethequestionofacause-and-effectrelation-shipbetweendeficienciesandviraldisease.Wewillreturntothissubjectinthenextchapter.

170 Healthy Crops

Table 11: Ratios between various elements in rice, according to their state of resistance to Piricularia.

Ratios Values in healthy rice Values in diseased rice

KCaCa/MgCa/NaK/NaP/SN/CuP/MnBase/AcidMacro- elements/Mn

7.61.52.1

19.16.4

35.035.6

3.6231.0

2.04.0 2.26.42.2

54.7118.4

2.3656.0

In regard to rice, the authors point out thatmanganese decreaseswithsubmersion.Theyalsostressthegreatimportanceofcopper.Theirconclu-sionisasfollows:

‘Itisclearthatthecontaminationofthesoil,water,andseedswith‘blast’sporeshasnoinfluenceonthehealthoftheplantwhentheplant’snutri-tion iswellbalanced. Even in susceptible varieties, the disease does notpersist.Wecanacceptthatlevelsof18ppmofMnand2ppmofcopperaresufficienttokeeptheplantsingoodhealthinthesoilsstudied.’

We have looked at the effects of different types of fertilisation on theresistance of the rice plant to its different parasites. The results show thegreat importance of the plant’s nutrition in the stimulation of proteinsynthesis.Herbicidesmakericesusceptibletoitsparasites,andthisistrueofcerealplantsingeneral.Theydothisbyinhibitingproteinsynthesis,andthroughimperfectselectivity.Justtheoppositehappenswithawell-balancedfertilisation.

Although thisphrase, ‘well-balanced fertilisation,’ is a common-place, itisneverproperlydefined.Wedefineitasobtainingamaximumdegreeofproteinsynthesis,especiallyduringthemoresensitiveperiodsoftheplant’sphysiologicalcycle,suchasflowering.Toachievethis,wehavetounderstandtheneedsofeach individualplantandnotpoisonitwithonepesticideoranother.


Astoperfectingtheuseof fertilisers, this isasubtlequestion,giventhestateofourknowledge. It canonlybe achieved through the correctionofdeficiencies.Thisis,moreover,thereasonwhyallpreventivemeasuresthatadheretosuchamethodmustbebasedonexaminingboththesoilandtheplant.Weshallreturntothisinthecourseofthenextchapter,inwhichweexaminenutritional treatments with leaf sprays.

Notes1 Somerecentanalyseshaveshownthatanincreaseinnitrogenfertilisation,from150

U/haNto250U/haN,leadstoadecreaseofvariouselementsincolzacrops15%inS,11%inB,8%inMo,3%inMnwhileNincreasesby10%.

172 Healthy Crops

Chapter 9

Correction of Deficiencies and Stimulation of Protein Synthesis

to Prevent and Control of Diseases and Parasites

I. Introduction

The nutritional requirements of insects, pathogenic fungi,bacteria,andvirusesarenotidentical.Instead,theyalldrawfromthe available ‘pool’ of free amino acids and reducing sugars. It isthestateofproteolysiswhichsensitisestheplanttoitsparasites.InChapter2,welistedthevariousfactorsthatarelikelytoinfluenceproteinsynthesis.Theycanalsobeclassifiedaccordingtothedegreeofcontrolthatthefarmerhasoverthem.Heorsheismostoftensubjecttothevarietyoftheplant,sometimestherootstock,thesoil,andtheclimate.Thefarmerhaspoweroverfertilisation,grafting,andchemicaltreatments.

Fertilisationofthesoilandfertilisationofthefoliageshouldworktogether tobringaboutoptimumlevelsofproteinsynthesis.Thisassuresbothprotectionagainstparasitesandthenutritionalqualityoftheharvest.

Inpractice,thisoptimumnutritioncanbeseenfromtwoangles:• themajorelements, notablysuch ‘traditional’onesasN,P,

and K, to which can be addedCa,Mg, and others which,owingtotheirproperties,mightbebettergroupedwiththemicronutrients.

• themicronutrientsthebestknownofwhichareCu,Fe,Zn,Mo,Mn,Li,B,Co,Ni,andI.WemightalsoaddCr,F,Se,Sr,andVa.

173 Correction of Deficiencies and Stimulation of Protein Synthesis to Prevent and Control Diseases and Parasites

Giventhelengthofthislistandhowlittleweknowabouttheroleoftheelementsinthephysiologyoftheplant,itiseasytofeeldiscouragedinthesearchforthenutritionalbalancethatallowsustoensuresimultaneouslythehealthoftheplantand(moreambitiously,tobesure)thatofthepeopleandanimalsthatconsumeit.

Firstwemustdiscoverhowtoavoiddeficienciesandthenhowtocorrectthemasfaraspossible.Itseemsthat,withoutrealisingit, traditionalanti-fungalmeasureshaveoftendonethis.

Thischapterincludes:

• astudyofthebalanceofthecationicelements,deficiencies,andnutri-tionoftheplant,

• astudyofthewayvariousanticryptogamswork,• aspecialstudyofboronanditsproperties,• anexampleoftherelationshipbetweendeficienciesandviraldiseases,• thecontrolofscab(currentdifficultiesandnewperspectives),• variousexamplesofcuringdiseasesthrough‘nutritional’sprays.

II. Cationic balances and the nutrition of the plant

VariousresearchershavestudiedthebalancebetweenthecationicelementsK,Ca,andMg,althoughlessresearch,itseems,hasbeendoneonsodium.Thesestudieshavebeencarriedoutusinganumberofmethods:hydroponiccultivation,leafanalysis,effectsonthescion,andtheeffectsoffertilisersonthesoilorofspraysonthefoliage.

However,itisnotonlycationicbalancesthatinfluencethisbalance.Themicronutrients intervene just asmuch.The reason is simple: they consti-tutepartof thecoenzymes,andas such they intervenedirectly inproteinsynthesis.

Mn,Cl,andBareactivators of enzymes,whileCu,Fe,Zn,andMoarecomponents of enzymes.Thisexplains the importanceof theirrelationshipwithK,Ca,andMg.Finally,regardingthecriterionoftheplant’s‘resistance,’thisexplainstherelationshipsofMn,Cl,andBwithoneanotherandwithnitrogen, and the equilibria between the different forms. There aremanymysteriesregardingthissubjectstilltoberesolved,andthisisconfirmedbythevariousstudiesinthischapter.

174 Healthy Crops

1. K/Ca and K/Mg ratios

Potassium seems to be the element that, both in soil fertilisation andfoliagenutrition,mostoftencreatesresistanceintheplanttowardparasiticalinsectsanddiseases.Kactivatesenzymesandoverfortydifferentenzymesareinterconnectedwiththiselement.Accordingly,aKdeficiencyleadstoanincreaseofsolublesubstancesinthetissues.Theseincludereducingsugarsandsolublenitrogenouscompounds,especiallytheaminoacidsasparagineandglutamine,essentialnutritionalfactorsforparasites.

HighdosesofKlowertheproportionofaminoacidsandstimulateresist-ancetovariousdiseases.

ThisinfluenceoftheionK(sinceKisanon-componentpartoforganiccompounds)explainshowitcaninteractwithanumberofotherelements,includingmajorones suchasCa,Mg,andN,andvariousmicronutrientssuchasiron,zinc,molybdenum,andboron.TherelationshipswithCaandMgarelikelytobeofmostinterest,sincetheirbalancewiththesecationicelementshasthegreatesteffectonthemetabolismofproteinsynthesis.

Calcium is equally important for plant resistance. Shear (1875) lists nofewerthanthirtydisordersordiseases,inthestrictsense,arisingfromcalciumdeficiencies.Amongtheseareanumberofdifferentnecrosesor‘blackhearts’(aninhibitionofthemultiplicationofthemeristemcells).

WeknowinfactthatCahasaneffectonsomeenzymesandonthecircu-lation of carbohydrates, while certain proteins have some affinities withcalcium.Inthiswaycalciumencouragesthesynthesisofamylase.ItplaysanimportantroleintheSiCabalanceandkeepstheclayinaflocculatedstate.ItalsodeterminesthepHvalueofthesoilandthusthelevelofbacterialactivity.

These various functions explain the close relationship that calciumhaswith various other elements. Thus, while it can prove beneficial in exer-cisinga‘buffering’effectoncertainmicronutrients,itcanalso,intheformofcalcareoussoilimprovers,blockmanganeseincereals,zincinmaize,orboroninbeetroot.Arelationshiphasalsobeennoticedbetweencalciumandmolybdenum,aluminium,andstrontium.

Aborondeficiencyarisingfromacalciumdeficiencycanleadtoformationof‘proliferations’or‘witches’brooms,’causinggrowthfailureinmeristems,aswehaveseenabove.


AsaresultoftheimportanceofthetwoelementsKandCaforthephysi-ologyoftheplant,itisinterestingtostudytheinfluenceoftheK/Cabalance.WeshallalsoconsidertheK/Mgbalanceasacriterionforthelevelofproteinsynthesisatagivenstageofthecycle(eg:floweringorripening).

TheequilibriumbetweenKandCahasbeenstudiedbyCraneandSteward(1962)inMentha piperita,cultivatedinahydroponicsolution.Theeffectsonthesynthesisofproteinsandtheiraminoacidcompositionwerealsostudiedinrelationtothelengthoftheday(inotherwords,thephotoperiod)(Fig.2)

On longdays there isprotein synthesis inconditionsofhighglutaminecontent,withgrowthoccurringinproportiontoanelevatedK/Caratio.

Onshortdays,growthoccursaccordingtoarelativelylowK/Cabalance,whilelevelsofsolublenitrogenarehigherandthoseofproteinnitrogenarelower.Proteolysisdominates,withanaccumulationofasparagine.Asparagineis anaminoacid required for thegrowthof fungi (we shall return to thisinrelationtofruitscab).Itaccumulatesinthoseplantsthatarespecificallyfertilisedwithammoniumnitratefertilisers.Thiscouldexplainthesuscepti-bilitytodiseasecausedbythistypeoffertilisation(HuberandWatson,1974)andatthesametimetherenewalofattacksinthelateautumn.

Generally speaking, a Ca deficiency reduces the quantity of proteinproduced, with sudden cessation of growth. On short days K deficiencybrings a drastic increase in asparagine and on long days, an increase inglutamine.Similarphenomenaarealsofoundinotherplants.Althoughtheeffect ofKon themetabolismof nitrogen is still very poorly understood,neverthelessanalysesofplantsdeficientinKshowincreasesinsolublenitratecompounds,inparticularaminoacids,whileproteinsarefoundtodiminish.Such resultshighlight the relationshipbetween theK/Cabalance and theplant’sresistancetovariousparasites.

The K/Mg balance

Magnesium is, of course, part of the chlorophyllmolecule. It thereforeformspartofthechainofdecompositionandofcarbohydratesynthesis.ThereactionofADP+PtoATPcannottakeplacewithoutMg.ThisexplainstheimportanceoftherelationshipbetweenPandMg.

176 Healthy Crops

The fact that themetabolismofphosphorus is closely related to thatofcalciumexplainstheCaMgantagonism.ThisiswhytherelationshipbetweenKandCamaybeusedasafirstapproximationtostandardisethemetabolismof the plant, especially with respect to protein synthesis. In some plants,however,itismagnesiumthatseemstobethemostvariable,dependingonconditions.Thisisso,forexample,inthecaseofthegrapevine,wherespecialstudieshavelookedattheeffectoftheK/Mgrelationshiponthenutritionoftheplant(Delmas,1970)andonthepracticaluseofleafdiagnosisforsimilarends(Ryser,1982).

TheworkofDelmasonMerlotcultivatedinanutrientsolutionaimedtoassesstheeffectsoftheelementsN,P,K,Mg,Fe,Mn,B,Mo,andZnonthevegetativestateofthegrapevine,andespeciallythepotentialfordeficiencies.

According to Delmas (op. cit.), magnesium deficiency occurs at levelsbelow0.20%ofdrymatter,andaproportionofKhigherthan1.5%,andthusadeficiencywhentheK/Mgratioishigherthan7.Thisproportionissimilartothatestimatedbyotherauthors(LevyandGouny,forexample).

Thisratiovariesgreatlydependingonthenatureoftherootstock,aswehave seen inChapterVII.Thus theK/Mg ratio in the leaf blades followsthescalebelow(Table12),dependingonthenatureof therootstockused(Duval-Raffin,1971).

Table 12: Values for the K/Mg ratio in the leaf blades of Merlot, in relation to the rootstock (DuvalRaffin, 1971)

Root system Mg: mg/kg Dry Matter K/Mg ratio

Merlot ungrafted Merlot/SO4 Merlot/3 309 Merlot/Riparia

2 110 7651 009 912

5.3914.2711.2817.09

Astheauthorpointsout,KandMginthegrapevineareprofoundlymodi-fiedbygrafting,soweneedtodeterminetheK/Mgratio.SoilspoorinMgcauseMgdeficiencieswhichimpactonnutritionandthusontheresistanceoftheplanttodiseasesandparasites.Thishappensinthecaseofgrapebunchdesiccation.


According to Ryser (1982), there is a ‘latent’ deficiencywhen the ratiois around 1012, as can happen in some vineyards in French speakingSwitzerland.Thestandardratioinviticultureisbetween2and10.AnetMgdeficiencyoccurswhenthereisaratioofmorethan12.

Suchfiguresprovideabasisforcorrectingdeficienciesandthus,asweseeit,forcontrollingparasites,especiallybynutritionalsprays.

However,thecationicelementsK,Ca,andMgarenottheonlyonesthataffectthemetabolismoftheplant.Themicronutrientsseemtoplayaveryimportantrole in thisrespect,due to theirrelationshipwith theenzymes,whilemuchremainsunknownabouttheirrelationshipwithK,Ca,andMg.Phenomenasuchasblockingandstimulationmayoccur,althoughtherulesthatgovernthesearenotyetclearlyestablished.

2. The balances between micronutrients

Inhisexperimentswiththegrapevine,Delmas(op. cit.)hasbroughttotheforetheimportanceofcertainmicronutrientratiosatthelevelofdiet,espe-ciallytheFe/Mnratio.Optimumratioswouldbeontheorderof1duringthefloweringperiodand0.6duringripening.AMndeficiencycausesratiostoexceed5.Tobemoreprecise,suchaMndeficiencyleadstoseriousmetabolicproblems,whichareallthemoreimportantsince

• thelevelofPrises;• thefeedlevelofiron,previously,wasreducedorexcessive.

Finally,wealsonotetheexistenceofaK/Mnbalance,withtheMndefi-ciencyleadingtoanaccumulationofKintheroots.Atthesametime,aKdeficiencyistheresultofamanganesedeficiency.

Inbranchtendrils,aMndeficiencyprovokesadisturbanceoftheFe/MnandP/Mnratios.Thelatterratiocouldinfluencetheripeningofgrapesthatareundernourished,small,andrichinP.

Thisinteractionamongthenutritionalelements,especiallythemicronu-trients,isrelatedtotheabsorptionofthoseelements.Primavesiet al.(1982)pointoutthatinricetheabsorptionofMnmayriseto8,000ppmincertainvarietieswithoutanysideeffects,bycounterbalancingMnlevelswiththoseofFe.Inconclusion,theFe/Mnratiocouldbeagoodchoiceasanindicatorforplantmetabolism.

178 Healthy Crops

Lubetet al.(1983),confirmingtheimportanceoftheroleofironinthedietandthusintheplant’sresistance,emphasisethatasameansofanticipatingzincdeficiencyinmaize,theFe/Znratioappearedtobeamuchbetterindi-catorthanthezinccontentassuch.Weknowthatthelatterisaconstituentof numerous enzymes. This explains better the histological modificationscausedbyfunctionalproblemsintheenzymechains.Znactsasanessentialelementformanymetalloenzymesofthedehydrogenasetype.

Werecall thecloserelationship linkingzinc to themetabolismofphos-phorousinthegrapevine.ZincbasedtreatmentsleadtoanincreaseinthePcontentintheleaves-thatistosay,inorganicphosphates,phospholids,andnucleoproteins (Dobrolyubskii and Fedorenko, 1969). Such results couldexplain thebeneficialeffectsnotedbyDufrenoy(1934)withzincsulphatetreatments against the manifestations of infectious degeneration in thegrapevine.

Zincdeficiency,especiallyinthetomato,causesanincreaseinthelevelofaminoacids,withaconsiderableaccumulationinparticularofasparagine,because it cannot be polymerised into proteins (Krisna, 1963). From thisarisegrowthproblemsandsusceptibilitytodisease.

Finally,wedrawattentiontotherelationshipbetweenmolybdenumandtheotherelements.Delmas(op. cit.)indicatesthataModeficiencycausesleavestobedeficientinKbutenrichedinCa.TheratioK/Capassesfrom0.22ofdrymatterto0.12duringtheripeningperiodandfrom0.37to0.07after harvesting. Delmas also noted that an Mo deficiency provokes anenrichmentoftheleavesinMn.

According to Primavesi et al. (1972) a delicate balance exists betweencopperandnitrogen.ThustheN/Curatiois35.0inhealthyriceand54.7inriceinfectedwithPiricularia.

InMentha piperita a copperdeficiency encourages the accumulationofsoluble compounds, especially glutamine. If copper treatments actuallyenrichthetissueswithcopperandhaveaneffectonproteicmetabolism,thiswouldexplainitseffectivenessagainstvariousdiseases.(Seebelow,p.226).

Boron is another element whose deficiency has often been linked tosusceptibilitytodisease.


Tabl

e 13

: Fo

liage

ana

lysi

s of

tom

atoe

s h

ydro

solu

ble

elem

ents

in m

g/kg

Elem

ents

NH

4PU

4K

CaM

gFe

CuM

nZn

BCo

CdTi

Ni

Mo

Subj

ects

Hea

lthy

tom

atoe

s10

00

3125

48

50

3375

14

75

115.

0 62

.540

137.

516

07.

55

2.5

92.5

12.5

‘Viru

sed’

tom

atoe

s 12

5031

2549

0019

2514

0010

7.5

15.5

11.5

115

110

TT

T13

7.5

32.5

N

.B. T

= T

race

s

Tabl

e 14

: Ra

tios

whi

ch in

dica

te d

efici

enci

es

Elem

ents

K/Ca

Ca/M

gP/

CaK/

MFe

/Mn

P/M

nN

/Cu

N/P

Subj

ects

Hea

lthy

tom

atoe

s

1.4

2.

28

0.92

3.

28

2.87

78.1

2 16

0.

32

‘Viru

sed’

tom

atoe

s2.

4

1.39

1.

62

3.50

9.

24

271.

7 80

.64

0.40

N. B

.: M

n, C

u, a

nd C

a de

ficie

ncie

s in

tom

atoe

s w

ith v

irus.

180 Healthy Crops

III. Deficiencies and viral disease in the tomato

Severalyearsagoanagriculturalchemicalsfirmprovideduswiththeresultsofananalysisoftomatoeswithandwithoutvirus.Thedifferencesbetweenthemproved tobevery significant.Thisparticularfirmaddedobjectivelythatitseemed‘extremelydifficulttoknowifthesedifferenceswereduetothevirusesoriftheyarosesubsequenttofeeddeficiencies.’

Webelievethatitisthedeficiencythatcreatesintheplantastateofsuscep-tibilitytodisease,evenif,oncethevirusisestablished,bothsymptomsanddeficienciesbecomemorepronounced.Asfarastheprecisedetailsofhowaviraldiseaseistriggeredareconcerned,Dufrenoy(1934)notedinthecaseof‘mottleleaf’:‘Thepathologicalcasesarelinkedtoprematureappearance,aswellastoageneralcellularproteolysisandpecticdegeneration’.

Thisproteolysisincitrustissuesinfectedwith‘mottleleaf’wassatisfactorilyhaltedbyZnSO4basedspraysneutralisedbylime,asinBordeauxmixture.

Tables13and14showtheresultsoftheanalysisinmg/kgoftomatoleaves,with and without virus respectively. Some ratios provide more specificevidenceofcertaindeficiencies,whichapparentlycauseproteolysis.

Thus,Ca,Mn,andCudeficienciesareallfoundsimultaneously.Copperandmanganesedeficienciesseemtobethemostpronounced,althoughwecannot saywhat precisely is responsible for the disease.However, on thehypothesisthatcoppertreatmentscouldprovetobeeffectivetosomeextentagainstbacterioses thiswouldmerelybedue to thebeneficialeffectof thecopper onproteinmetabolism in the tomato.This conclusion leads us tostudy the anti-fungal action of various ‘fungicides,’ both ‘traditional’ and‘synthetic.’

IV. On the mode of action of various anti-fungal products

Itisevidentthatweknowverylittleabouthowanticryptogamicproductswork.Wemayarrivequicklyatthepointwhereweknowthatthisorthatformulaismoreorlesseffective,butwewouldprogressmorequicklyifweknewwhy.This,then,isgoodreasontotakeintoaccountthereactionoftheplantintheanalysisoftheproduct’seffectiveness.


1. Copperbased products

ThefamousBordeauxmixturewasdiscoveredwhenit ‘wasnoticedthatthe vine stocks at the end of each row of grapevines,when sprayedwithvitriol (coppersulphate) inorder toprotect themagainst thieves, sufferedfewer attacksofmildew.Following this,Millardet andGayonbecame the‘inventors’ofBordeauxmixture,’intryingtoexplainhowtheprocessworks.

EvenwithBordeauxmixturetherearesometimessetbacks.Aftermildewattacksin1932,thevalueofcoppertreatmentswascalledintoquestionbyadvancingtheoldcliché,‘Themildewhasbecomehabituatedtocopper.’(Atthisstagetheword‘resistance’wasnotyetincirculation.Someauthors(suchasVilledieu(1932))saidthatanexcessofnitrogenandphosphatefertiliserscouldhavemade thegrapevinemore susceptible.Even in that era, ithadalreadybeenshownthatthesefertilisersencouragedtheinvasionandmulti-plicationoffungalparasitesofthegrapevine(Schaffnit).

ThecopperquestionwastackledbySemichon(1916).Theeffectivenessofcopper,evenonthesurface,doespresentsomeproblems,aswesawabove.Semichon(op. cit.)distinguishedbetweenthe‘surface’copperthatremainson the leaves and the ‘absorbed’ copper.He observed that the surface or‘reserve’coppercanonlyprotectthegrapevineforaveryshortperiod.Thisisforthesimplereasonthat‘thecopperhydrates,copperhydrocarbonates,andtetracoppersulphatewhichremaininthegreenpartsofthegrapevineafterapplicationbecomelessandlesssolubleduetotheeffectofatmosphericagents.’

Itisinterestingtonoteatthispointthat,accordingtoSemichon(op. cit.),leaves which are burnt by copper are immunised againstmildew. Yet thequestionremains:howdoesthecopperwork?Shoulditbeconsideredasasortoftoxicwall,afterithasparticipatedinthemetabolismofthegrapevine?Orshouldonenot, instead, lookmorecloselyat therelationshipbetweencopper,plant,andparasite?

Copper,mediated by its action on enzymes (the oxidases), acts on thenitrogenmetabolismoftheplant.Thusitparticipatesinproteinstructure,incombinationwiththesubstrate(Malström,1965).Thisexplainshowvineleaves treated with Bordeaux mixture can produce much lower levels ofsolublenitrogenincomparisonwithotherchemicalproducts(Pinon,1977).

182 Healthy Crops

Crane andSteward (1962)have established, regardingMentha piperita,that copperdeficiency in thenutrient solutioncausesproteolysis,withanaccumulation of glutamine in the tissues.One can therefore imagine thatapplication of copper through foliar treatments could have the oppositeeffect.Similarly,AgrawalandPandey(1972),experimentingonwheat,wereabletoshowthatcoppertreatments,byallowingsugarstobebetterutilised,increaselevelsofproteinnitrogenincereals.Apositiveeffectsuchasthisonproteinsynthesiswill,inourview,onlyservetostimulatetheresistanceoftheplant.

TheworkofMarchal(1902)onlettuceshowsthatcopperappliedatlevelsof5to7/10,000inthenutritionalenvironmentpreventsthedevelopmentofMeunier(Brema lactucae).

Conversely, copper deficiencies resulting from the use of productscontainingnitrogen(fertilisersinthesoilorchemicalpesticides)couldmakecrops susceptible to variousparasites.This is thequestionwehaveprevi-ouslyconsideredinregardtothecurrentspreadofbacterialdiseases.InthisrespectonecouldperhapsrefertotheN/CuratiosuggestedbyPrimavesiet al.(1972)inrice.

2. Sulphur

Priest (1963)mentioned thatduringmore than2000years that sulphurhasbeenusedtoprotectcrops,ithasneverbeenusedasafungicide.Nowitisusedassuch,especiallyinthecaseofOidium.

Thatsulphurcannotbeusedonitsownasa fungicide isprovenbythefactthatsulphurparticlescannotpenetrateintofunguscells.However,someearlywritersobservedthattheeffectofsulphurincontrollingOidium onthegrapevine,which they called ‘remarkable,’wasprincipallydue to ‘thewaysulphuraffectsthevegetationoftheplantgenerally.’Oneofthemgavethefollowingexplanation:

‘Grapevineswhich are sulphured, especiallywith a very fine spray, feeltheeffectofthisexcitationwhentheyaresick.Immediatelythepaleandshrivelledleavesstarttobecomegreen,supple,andshinyagain,andthevine branches start to grow. If the disease is not too far advanced, it isnoticeable how thewhitish efflorescencewhich has begun to cover theberriesdisappearsinthesamewaythatparasitesdoggingananimalbegintodisappearwhenitisfedaplentifulandhealthydiet(Martres,1862).’


Suchapertinentobservationaboutthebeneficialinfluenceofsulphur,byits indirect effecton thephysiologyof theplant, ties inwith thequestionposedbysomeauthorsabouttheinfluenceofthenutritiveenvironmentonthe vitality of the spores. Recent observations effectively confirm such anindirecteffectofelementarysulphur.AnexampleofthisisthetreatmentbysulphurinoaksagainstOidium.Observershavefoundthatsulphur,unlikeother chemicals, benefits the oak foliage. They conclude, ‘The beneficialeffectofsulphurisnotdirectlylinkedtoitspowerasafungicide.’(MaennleinandBoudier,1978).Howthendoesitwork?Inthiscasetoo,theanswermaybefoundbylearningwhathappensinthecaseofsulphurdeficiencies.

CraneandSteward(op. cit.)haveshownthatinMentha piperita sulphurdeficiencyinthenutrientsolutionleadstoan‘importantchangeinthebalanceofnitrogen,favouringthesolublepart,chieflyglutamineandarginine,andoverthecourseofthelongerdaysofsummer.’Thissuggeststhatsulphurisa‘plastic’elementcloselyassociatedwithproteinsynthesis.Moreover,therearenumerousauthorswhohaveunderlinedthecloselinksthatexistbetweenthemetabolismofsulphurandthatofnitrogen.

We know that plants that are rich in nitrogen and poor in sulphurcontainlargequantitiesoffreeaminonitrogen,nitrates,andcarbohydrates.Thisphenomenon is linked to adecrease in the reductionofnitrates andto reduced protein synthesis, together with a higher level of proteolysis(Nightingale,1932andEaton,1941).Ithasbeenshownthattheleavesareabletoabsorbthiselementarysulphur,becauseitislaterfoundintheplant’sproteins(TurrelandWeber,1955).

IfsulphurplayssucharoleinindirectlycontrollingOidium,thenitmighthave similar beneficial effects on plant diseases. Thus Dufrenoy (1936),stressing the damaging effect of deficiencies, as shown by the beneficialeffectofcertainfertilisers,recallsthatsulphurattherateof200to1200kg/hawas successful inFlorida in combating thebacterialdiseaseBacterium solanacearuminpotatoes.

Sothecorrectionofadeficiencyofsulphurthroughaprocessofanutri-tionalkind,atthesametimestimulatestheresistanceoftheplanttoitspara-sites.Thisactionofsulphur,byitspositive influenceonproteinsynthesis,wouldalsoappeartocomeunderthegeneralheadingoftrophobiosis.

184 Healthy Crops

BecauseCruciferae needhighlevelsofsulphur,itislogicaltoassume,asPolyakov and Vladinurskaya (1975) have done, that a sulphur deficiencydecreasestheresistanceofcabbagetoitsvariousparasites.

Soare thechemicalswhichhavealwaysbeenacceptedas ‘fungicides’ inactualfact‘remedies,’actingindirectlybyapositiveeffectonthemetabolismoftheplant?

3. How does maneb work?

If we look, for example, at a very widely used new ‘fungicide’ such asmaneb,wewillseejusthowdifficultitistoproveitseffectivenesssimplyintermsofitstoxicity.

ThisisthequestionposedbyVielandChancogne(1966).Initially,theyobservedthatifmanebissuspendedinwater,itabsorbsoxygenanddecom-position takes place: themanganese ismade soluble. Perhaps there couldbeanindirecteffectthroughthereactionoftheplanttothesolubilityofthemanganese.Thisisinfactwhathasalreadyhappenedwithcaptan.

4. Is captan itself a fungicide?

This is the question that can be posed in the light of the results of theexperimentsofSomersandRichmond(1962)toverifythepossiblesystemicactionofthischemical.Weshouldpointoutthatwearedealingherewithaphthalimide,aderivativeofsulphur,withtheformulaC9H8Cl3NO2S.

Somesolutionsofcaptanhavebeenappliedtobeansthroughirrigation,duringexperimentstocontrolBotrytis fabae.Analysisshowedthepresenceoflevelsofcaptanintheleavestobesolowtheycouldnotexplainanypossiblechemotherapy effect through systematic activity.The authors came to theconclusionthatsucheffectivenesscouldonlybeinterpretedas:‘interferenceinthemetabolismofthehostplant,whichisresponsiblefortheanti-fungaleffectobservedintheleavesafteranapplicationhasbeenmadetotheroots.’


5. How fosetyl (phosethyl) Al works

The new fungicide fosetylAl seems to have opened up ‘new avenues inthecontrolofplantdisease’(Bompeix,1982).Ashewrites,‘Contrarytothemajority of fungicides, systemic or not, fosetylAl (or aluminium trioeth-ylphosphonatewith the formulaC6HAlO9P3) is characterised by a weakdirecteffectonfungus.Thiseffectisnotsufficienttoexplaintheverygoodresultsobtainedinpractice.’

Onenotesanaccumulationofpolyphenolsthatpresumablyhaveafungi-toxiceffectonthehyphaefoundatthislevel-thatis,atthelevelofthenecroticblockingzones.Mightnotthisaccumulationofpolyphenolsbeaccompaniedbyadeclineinthenutritionalsubstancesrequiredbythefungus?Itwillbenotedthatnecroticblockingzonesalsooccurwithcopper.

Bompeix(1981)concludes:‘Allthesefactspointtoamodeofactionsituatedatthehost/parasiteinterface,notadirectactionontheparasitesthemselves.’Researchisstillbeingcarriedoutonthissubject,whichnodoubtwilldetectwhetherthisimmunityoftheplantorgancausedbythechemical,iscausedbyatoxic or even an abiotic mechanism.

Insummingupthissection,devotedtothestudyoftheeffectsofvarioustraditionalorchemicalantifungalproducts,wecanstatethattheprocessofeffectivenessproceedsthroughthereactionoftheplanttothepesticide.Theinhibitionof growthofpathogenic fungi couldderive fromanabsenceofnutritionalfactors.

V. Boron in plant physiology and resistance

1. The physiological role of boron: its balance with the other elements

Boronisthemicronutrientmostoftenviewedasthecauseofplantresist-ance,becauseofitseffectsontheplant’sphysiology.Yetitsmodeofaction,likethatofotherelements,stillremainsverymysterious.Mostknowledgeoftheroleofthevariousmicronutrientscomesfromstudyingthephysiologicalproblems caused by the lack of them. While boron does not seem to beessentialforanimals,theoppositeistrueforallplants.

Aswehavepreviouslynoted,borondeficiencyhasbeenlinkedtonumerousdiseases,whetherfungal,bacterial,orviral.However,borondeficiencyalsoaffectstheresistanceoftheplanttocertaininsectpests,suchasmites, forexample.

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Conversely,applicationsofborontothesoilorintheformofleafsprays,or even by impregnating seeds, stimulate the plant’s resistance to certaindiseases.

The relationship between boron and calcium

Calciumdeficiencies,whetherspontaneousorduetoaborondeficiency,oftenshowupthroughashorteningoftheinternodes,givingrisetosometypesof ‘witches’brooms’.Thishappensespeciallywiththemaritimepinethatgrows in soilsdeficient incalcium.Calcium is linked toanumberofenzymatic activities. In the plant, it is displaced in an upwards direction.AccordingtoPolyakov(1971),calciumactsbyincreasingthetotal levelofphosphorusanddifferentgroupsofphosphorouscompounds.TheroleofmicronutrientssuchasBorCuistointensifyCapenetrationintothecells.

This ‘synergy’, well known between certainmicronutrients, also comesintoplaywithboron.D.Bertrandemphasisesthefactthatborononitsownhasnosignificanteffect;it is only in the presence of Mg, Mo, and Mn (the 3 Ms) that the properties of boron become apparent.

Moreover,thewell-knownfactthatthereisarelationshipbetweenboronandthe transportofsugarswouldexplainthenecessityof itspresence fortheprocessofresistance,thankstoitsactioninprovidingthecarbonchainsrequiredforproteinsynthesis.

Whatarethefactorsthatprovidetheplantwiththeboronitneeds?Whatantagonistic factorswouldbeopposedeitherto itsverypresence,orto itsavailability?

2. The availability of boron and the requirements of the plant

The principal factors capable of affecting the availability of boron inensuring thehealthy functioningof theplant’sphysiologycanbeput intothreecategories:

• thetypeofsoilanditspH• fertilisation• pesticideintervention.

Asregardsthesoil,Coppenet(1970)observedthatmanyareasaredefi-cientinboron,forexample,intheFrenchMoyenne-GaronneregionandtheregionaroundToulouse.


Borondeficiencieshavebeenrecordedinawiderangeofcrops:appletrees,cauliflowers, alfalfa,beetroot, andgrapevines.Thus there couldbea rela-tionshipbetweensuchdeficienciesandthefrequencyofcertaindiseases.Itisperhapsnocoincidencethat,forinstance,flavescencedoréeingrapevines,whichinextremecasesresultsfromtheproliferationofamycoplasmaoravirus,isparticularlywidespreadintheArmagnacregion.AborondeficiencywaslateridentifiedinthevineyardsofGersandLotetGaronne.

Boronreservescannotbeactivatedinneutraloralkalineconditions.Cl.Huguet(1970)noticedthatboronisthemicronutrientmostoftendeficientinperennialplants,especiallyinappletreesandgrapevines.Ashestressed,moreover,‘Pebblysoilsdonotprovidesufficientamountsofboroneithertograpevinesortocherrytrees.’Onemightponderthereasonforthis-insuffi-cientboroninthebedrock,orparticularlypoorconditionsforthedissolvingoftheboron?Inthelattercase,shouldwenotalsohavetoconsideralackoforganicmaterialandtheroleofmicro-organisms?Wewillreturntothispointlater.

Towhatextentdoinorganicandorganicfertilisersaffecttheavailabilityofboronand,inabroadway,thatofmicronutrientsingeneral?

As has been noted, micronutrients constitute less than 1% of the dryweightofplants.Sowhyisitthatdeficienciesintheseelementsarerecordedsofrequently?ItseemsthatCoïc(1971)hasansweredthisquestion,whenhecommented: ‘Inageneralway, a factorwhichaffects theplant’sphysi-ologymayalsoaffectitslevelsofmicronutrients.’Amongthesefactors,Coïcmentions attempts to increase yields that actually produce an increase oforganicmaterialandthereforeadecreaseintheconcentrationofmicronutri-entsintheplantsandintheiryieldsingeneral.

The‘intensive’agricultureusedtoincreaseinyieldsisbasedonchemicalfertilisers,especiallynitrogenousfertilisersandpesticidespracticallyallofthemnitrogenousandchlorates.Aswehaveseeninthiswork,theparasitesthenfollowoneafteranotherinaninevitablecycle.Thisisbroughtaboutbytheplant’ssensitisation,whichmayitselfbethedirectresultofadeficiency.

Howdochemicalfertilisersandpesticidesinterveneinthisspecificcaseofthecreationofdeficiencies,especiallythoseofmicronutrientsand,morespecifically,boron?

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First, disregarding slag, which is fairly rich inmanganese, the amountof micronutrients provided by chemical fertilisers is insignificant whencomparedwithmanureorcompost.

Secondly,thesesyntheticfertilisersgenerallyincreasethepHofthesoil,thusloweringtheassimilationpotentialofthemicronutrientsMn,Fe,andZn.Forexample,becauseoftheantagonismbetweenPO4andZn,phosphatefertiliserscanengenderZndeficienciesinfruittrees,maize,andflax.

However, it is perhaps chemical nitrogen fertilisers, often used in highdosesinanefforttoforcehighyields,whichbearmostoftheresponsibilityfor blocking micronutrients. This is a phenomenon that has long beenrecognised for copper. It causes hypoglycaemia and lowered fertility inlivestock,when animals are fedwith fodder deficient in copper. PérigaudandDémarquilly (1975)note that, inBrittany, incidencesofpoor fertilityin cattle occur in areaswhere the soil is poor in copper, especiallywherefarmersmakeapplicationsofnitrogenexceeding100kg/ha.

As we mentioned in Chapter IV, in regard to bacterial diseases, suchblockage is linked not only to copper but also to boron. As Cl. Huguetshowed,applicationofnitrogentothesoilinincreasingdosescausesadropinboronintheleavesofcherrytrees(TableXV).

Inasecondorchard,whereatfirstnoborondeficiencywasfound,appli-cationsofnitrogenfertilisertothesoilcaused‘adecreaseinlevelsofboronthatbecamemorepronouncedoveraperiodofyears,asthetree’snutritionwasincreased.Itseemsthatwehavearrivedjustatpresentatalevelofboronwhich isno longer theoptimum for cherry trees’ (Table 15) (Cl.Huguet,1982).

Table 15: The decline in boron levels in cherry trees caused by nitrate fertiliser

Nitrogen fertiliser/ha Levels of boron in 1980 (ppm)

Average levels of, over 11 years (ppm)

Controls: 0100 kgs/ha200 kgs/ha

444032

474037

Further,Cl.Huguet(1982)studiedtheeffectsofapplicationsofzincandboronsprayedonthefoliageofcherrytreesoveraperiodoffiveyears.


Tostartwith,thetreesweresufferingfromborondeficiency,causingearlyblossomdrop.TheseresultsareputinconcreteforminTables15and16.

Table 16: The effects of treatments on the boron content of the leaves (ppm of dry matter)

Treatments Boron content (ppm) Nitrogen content %

Without boronWith boron

1959

2.382.56

Inthiscase,onealsonotesarelationshipbetweenboronandnitrogen,butinanopposite,beneficialsense.Thereareproteincompoundsthatbecomemorepronouncedfollowingacorrectionoftheborondeficiency.So,iftheNBrelationshipsometimesappearscontradictory,itisbecausetheyspringfromthestartfromdifferentcases-forexample,inthetwoorchardswhereCl.Huguetconductedhisexperiments.

1)Inthefirstone,thetree’snitrogenstatusrangedfromhightoveryhigh.Inotherwords,proteolysispredominated,withboronasthe‘limitingfactor.’Thisexplainswhy,undertheseconditions,applicationsoftoomuchNmakeborondeficiencymorepronounced.

2)Inthesecondcase,thetree’snitrogenstatuswascriticallylow,andtheboroncontentcorrespondedtoadeficiency.Thisiswhy:‘Theestablishmentofafeedwiththecorrectboronlevelscaninfluencethewholemetabolism,includingthenitrogenmetabolism,whichimprovesslightlyinthiscase.’(ClHuguet)What theauthormeansbythis is thatproteinsynthesis is inthiswayimproved.Fromthisstemthepositiveeffectsontheplants’resistancetovariousparasites,aswehaveseeninthecourseofthisbook.

3. The boron requirements of plants: Critical stages and application periods - effectiveness of sprays and boron treatments

Allthisdemonstratestheimportanceoftheboronrequirementsofvariousplants, especially fruit trees and grapevines. It also showswhere the defi-ciency threshold lies.AccordingtoRyser(1982),whoseresearchconcernsthepracticaluseoffoliagediagnosis,theratioN+P/Kcanbeusedtoassesstheriskofborondeficiency.Iftheratioincreases,thereisatendencytowardsastateof‘predeficiency.’Thisisaphenomenonofaquitegeneralkind,equallylikelytobefoundinviticulture,arboriculture,chrysanthemums,roses,andmarketgardens.

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Towhatextentcouldchemicalpesticides(largelynitrogenousandchlo-rinated), through repeated annual application, and by their cumulative,extended effects from one year to the next, upset the normal balance ofelementsandcauseaharmfuldeclineofboronintheplant’stissues?

Someanalysesmayperhapssufficetoprovidethekeytothecurrentdevel-opmentofbacterialandviraldiseasesinfruittreesandgrapevines,whichweareatpresentwitnessing.

Boron deficiency levels

Thenormisverysimilarforbothgrapevinesandfruittrees,andcanbedisruptedevenonageneral level inthesameway.Thegenerallyacceptednormput forward is 25ppm for the leaves and30ppm for the fullygrownfruit.

MmeHuguet(1979)proposesasanormallevelofboronamongapplesarangeof25to50ppmfortheleaves.Inthe‘Golden’variety,thecontentvariesfrom17to70ppm,anddeficienciescanoccuratlevelsof20to9ppm.Thesefiguresseemtoagreewellwiththethresholdof15ppm,generallyproposedasbeingabletoproduceseriousdeficiencies.

The best times for applications of boron in the form of leaf sprays arethoughttobethoseperiodswhentheboronappearstobemostcrucialforthemetabolismofthespecificplant.Boronis,besides,verymobile,andanetincreaseinthelevelofboronisobservedonlyashorttimeafterapplication.Thisnewlevelcanthusexceedthenormalleveltenfoldaftertheleaveshavebeentreated.

Nevertheless,sinceboronistransportedthroughoutthegeneralstructureoftheplant,levelsoftenreturntonormalafterspringtimeapplications,bytheendoftheseason,andoftenasearlyasthesummer.

In a general way, in fact, the authors admit that boron produces itseffect fromthebeginningof thefloweringperiod, inbothsunflowersandgrapevines.Inthecaseofsunflowers,accordingtoPolyakov(1971),cobaltbeginstoactbeforethefloweringperiod,whilecopperandmanganeseareactiveduringallstagesofdevelopment.Polyakov(op. cit.)alsoworkedonSclerotinia,obtainingexcellent resultsbysoakingsunflowerseeds insolu-tionsofboronandalsoofcobalt,manganese,andcopper.Saltswereusedontheseedsatlevelsof0.1%.


These saltshavebeen tested separatelybut, givenwhat is knownaboutthepropertiesofboronmentionedabove,itwouldbeinterestingtotryout‘complexes’bycombiningboronwith,forexamplethe‘3Ms’,i.e.Mg,Mn,andMo.

Inregardtotheboronrequirementsofperennialspecies,Cl.Huguetgivesthemasthefollowing:

Cherrytrees:10tonnesoffruit/harequire290gboronand230gzinc.Grapevines:Ugni blancgraftedonto4lBrequires108gB,75gMn,and

565gFe.

Formaximumabsorption,thebestperiodsforpeartreesareasfollows:boron:fromMarchtothebeginningofApril,manganese:aroundmidApril.

Forgrapevines,maximumabsorption: Boron:aroundmidAugust Manganese:aroundmidApril.

4. On the influence of different types of fertiliser on the availability of boron and other micronutrients for the plant

Thedataonthissubjectareveryincomplete.Wemustagainpointoutthatchemicalpesticidesandfertilisersmayblockmicronutrients.

Moyer(quotedbyVicario,1972)emphasisesthefactthatpesticidetreat-ments thatkilla largenumberof soilmicroorganismscan lead to toxicitytoward plants, which is attributed to a lack of availability of phosphorus.(Thisarisesfromaprocessthatisnotyetfullyunderstood.)

Moreover,MoyerpointsoutthatsomepesticidescontainingnitrogenarethemselvescationsandmaydisplaceothercationssuchasCa,Mg,andZn.Thisleadstobothtoxiceffectsanddeficiencies.

Similarphenomenamayoccurwithfertilisersforsimilarreasons.Bussler(1982)notesthat‘fertilisationwithhighlevelsofN,P,andK,thoughitcanleadtohigheryields,alsoincreasestheexportationofnutritionalelementsthatarenotreplaced.AnumberofreportsonmicronutrientdeficienciesinCa,Mg,andevenSconfirmthisrelationship.’

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Infact,casesofdeficienciesincopperaremoreandmorefrequent,espe-cially in cereals.Why specifically in cereals? Perhaps because ‘intensive’cultivation, as we have seen above, combines the harmful effects of bothfertilisers,especiallynitrogenousones,andchemicalpesticides,startingwithherbicides.Iftheblockageremainsasaresultofthesecultivationtechniques,onecanjustifiablyaskwhatuseis theapplicationofmicronutrientstothesoil?

However, organic fertilisers and applications of manure and silagematter improve the assimilation ofmicronutrients, especially boron.CoïcandTendille(1971)emphasisestronglythatcopper,ofwhichwehavejustspoken, is more easily assimilated thanks to the bacterial developmentlevelofthesoil.Thisisthesameforotherelements,especiallyphosphorusandboron.Thephenomenaofmicronutrientsbeingblockedinthesoilbychemicalpesticidescouldbetheresultofthepesticides’harmfuleffectsonmicroorganisms.Ontheotherhand,thesemicroorganismsareabundantinmanureandcompost.

It ispossible toseebacteriaaspackagesofenzymes.Thisexplains theirinfluenceonthephenomenaofassimilationcapacity,balances,synergy,andexchange.

Whilewaiting fornewresearch tobringus freshdataon the roleofK,Ca,Mg, andnumerousmicronutrients inprotein synthesis,wemust relyonwhatweknowaboutthecorrectionofdeficienciesinordertostimulateproteinsynthesiswithaviewtoachievingmaximumimmunityfortheplant.Wemustrely,thatis,ontheoptimumlevelofthevariousbalanceswehavelookedat(K/Ca,K/Mg,Fe/Mn,Fe/Zn,etc.)aswellastheperhapsmoreimmediateconsequences(N/Cu,N/Ketc).

Given how little we know about the process of protein synthesis, wecertainlycannotdenythatsuchanundertakingpresentscertaindifficulties.However,itcouldintheendpresentalesserriskthantheblindapplicationofpesticides(i.e.withoutpayingattentiontotheeffectseitherontheplantitselforonthelifeofthesoil).

Besides,we have also seen that it is probably through such an indirecteffectthatcopper,sulphur,orsomenewfungicidecanactto‘dissuade’thepathogenicagentfromattackingthespecificplant.


VI. Is it possible to control fruit scab by nutritional treatments?

1. The ‘resistance’ of fruit scab to chemical anti-fungals

Weshallnowlookathowitmightbepossibletocontrolacommondisease,namely fruit scab.Thenew fungicides arenotonlypowerless against thisdisease,butalsocausephenomenaofso-called‘resistance’(orproliferationbyprovokingsusceptibilityintheplant).

Fruit scab (Venturia inoequalis), together with mildew, Botrytis andOidiuminthegrapevine,manifeststrong‘resistance’phenomenainreactiontocertainchemicalfungicides.AccordingtoOlivierandMartin(1979),forexample,inanumberoforchards:‘Difficultiesintreatingwholetrees,linkedtorainmeasurementandassociatedwithanactiveparasitepopulation,haveledtothemorefrequentuseofbenzimidazoles(inparticularcuratives).Theconditions have promoted the appearance of phenomena of resistance tobenzimidazolesintheseorchards.’Theseauthorscontinue:

‘Aftertheobservationofthisinitialdamage,treatmentsweresteppedupandsometimesthedosesexceededauthorisedlevels.Evenso,theprogres-sionofthediseasewasnoteffectivelyhalted.Undertheseconditions,thefrequencyof resistant strains among infestations of fruit scab increasedsteadily.’Andfinally:

‘Ceasingtousebenzimidazolesdoesnotautomaticallymeanthatresistantpopulations will decline.’ ‘Observations of apple trees in Australia andGermany,andofpeartrees inIsrael,showedinsteadthatthesestrainsarebeingpreserved.WehavealsocomeacrossanidenticalsituationinFranceintheappleorchardswearestudying’(OlivierandMartin,1979).

Observationsof‘resistant’strainshavebeenconfirmedbyvariousparties.Thefollowingquotationsarefromapopulararticle(Phytoma,May1982):

‘Theresistanceofappleandpearscabtobenzimidazolebasedfungicidesis shownby the significantdamagewhichoccurs, in spiteofnumeroustreatments.’

‘Someresistantstrainsareinfactcapableofsurvivingforatleastfouryearsormore,evenwhennouseatallismadeoffungicidesofthischemicalfamily.’Andfurther:‘Insomeorchards,asingleapplicationofbenzimi-dazolesallowedaverysmallnumberofresistantstrainstodevelopunde-tectedduringtheautumn.’

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Lerouxcomments: ‘Inorder forresistance tomanifest itself inpractice(by a decrease in effectiveness), it is necessary that resistant individualsare selected (to the detriment of the sensitive ones). In other words, thefrequency of resistant individualsmust increase from one in amillion toaround2030%’(Leroux,1982).

Lerouxrecognisesthatthemodeofactionbehindthisselectionandthefactorsthatcontrolitarelargelyunknown.‘Manyoftheobservationsmadeinpractice involvesituationswhere thefinal stagehasbeenreached.Thatistosay,90to100percentofthepopulationsareresistantindividuals,andtreatmentiscompletelyineffective’(Leroux,1982).So,asPhytomaacknowl-edges:‘Notallunexplainedattacksoffruitscabcanbesystematicallylinkedtotheissueofresistance’(Phytoma,May1982).

Theseobservationssuggestthatthereismuchconfusionandthat,inthefaceofanunexplainedphenomenon,thetermsusedinanattempttoclarifyitarelikelytobeinadequate.Inthiscase,theterm‘resistance’isinadequatetodefineaprocessthatisnearlyimmediate,aswellaspersistent.

So might this phenonmenon be the result of proliferation? Is this thecase in the stimulation of the development of Botrytis in tomatoes (Coxand Hayslip, 1956), strawberries (Cox andWinfree, 1957) or grapevines(Chaboussou, 1968), by various dithiocarbamates (maneb, nabam, zineb)usedagainstOidium?(Seeabove,ChapterI).

Unlesscomparisonsaremadewithcontrolstreatedwithpurewater,onecannotdismissthehypothesisthatthediseaseisstimulatedbyanindirecteffect of pesticides on the plant’s physiology. If it is indeed a nutritionaleffectthatleadstotheappearanceofthispseudo’resistance’,whichmaybecomparabletoaproliferation,itwouldbelogicaltoassumethat,conversely,onemightobtainanti-fungalresultsbyusing‘nutritional’treatmentswhicharebeneficialfortheplant.Thiswouldespeciallybethecase,aswehaveseenabove,withtraditionalfungicidessuchascopperandsulphur.Thisiswhatweshallnowstudy, inregard tocontrolof fruit scab.Weshallbeginwithaninvestigationofthemechanismofthesensitisingoftheplantwewishtoprotect.


2. The nutritional requirements of Venturia inoequalis and the mechanism behind the sensitisation of the plant by new chemical ‘anticryptogamics’

Certainstudiesofhowdifferentsourcesofnitrogenpromotethegrowthand sporulation of various isolates ofVenturia inoequalis have shown, inparticular,that:

• Lhistidine is an excellent source of nitrogen for sporulation withcertainisolates,

• DLalanine,DLphenylalanine,DLasparagine,DLaminobutyricacid,Lprolineandglycineprovetobeequallygoodsourcesofnitrogenforsporulation(Ross,1968).

Inotherwords, thesamenutritionaleffects thatencouragesomeaminoacids(foundintheexudationsorinthetissuesthemselves)alsoencouragethedevelopmentofpathogenicfungi.

Might this statewhereproteolysisdominatesbecausedby theactionofsyntheticfungicides,andcouldthisbetheoriginofwhatisdesignated‘resist-ance’?Pathologistshaveremarkedonthefactthatthis‘resistance’isobservedpreciselywiththoseproductsthatinhibitprotein,sterol,andcarbohydratesyntheses.Ifoneacceptsthatpesticidesparticipateinthemetabolismoftheplant by penetrating its tissues, it is possible that, as a result of synthesisbeinginhibited,theplantmaybepredominantlyinastateofproteolysis,andthussusceptibletoparasitesfornutritionalreasons.

In otherwords, these ‘resistance’ phenomenawhichmultiply in such astrangemannercanperhapsbeexplainedasprocessesofproliferationwhichthemselves result froma sensitisingof theplant.Theplant is ina state inwhichproteolysispredominates,astatethatmayitselfhavebeencausedbyoneormoredeficiencies.

3. The provocation of deficiencies by synthetic pesticides

A. Soluble nitrogen and susceptibility to disease.

Lookingat therelationshipsbetweendiseasesandtheaminoacids,VanAndel(1966)emphasises:

‘Thefactthatthenitratenutritionoftheplantmayinfluenceitssensitivityindicatesthatnitrogenmetabolismplaysaroleofitsownintherelationshipbetweentheplantandthepathogen.’

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Phenoliccompoundshaveraisedhopesoffindingtoxicantagonistsoftheparasites(aswediscussedinChapter2).ToquoteVanAndel:

‘The effect of the phenolic compounds, which according to Flood andKirkhamhavebeenfoundtobeveryimportantintheresistanceofappletreestoV. inoequalis,wasfoundtodependonthenitrogenconcentrationoftheaminoacids.’

In other words, as we saw in Chapter 2, the phenols, like the otherphytoalexinesproposed,donotseemtohaveanysortoftoxiceffectonpath-ogenicfungi.Theyactasbalancingelementsfortheaminoacids,whichplayan eminent anddecisivenutritional role against theparasites.Thiswouldseem to confirm the findings of the same author. As he observes, ‘Someamino acids such as glycine, asparagine, aspartic acid, and glutamic acid,whichholdakeypositioninthemetabolismofnitrogeninplants,havebeenfoundtoincreasesusceptibilitytocryptogamicdiseases.’

Theinfluenceofsolublenitrogenonthesusceptibilityofappletreestoscabcanbefoundatthelevelofvarieties.AsWilliamsandBoone(1963)observe:‘TheCortland variety,which is susceptible to all strains ofVenturia inoe-qualis,hasanasparaginecontentof1.969intheleaves,whilsttheMcIntoshvarietyisresistantwithlevelsofonly0.756.’

Thevarietythereforeaffectstheresistanceprocessbymeansofthelevelofproteinsynthesisthatitisabletocreate,thoughthisvariesinaccordancewithlocalconditions.

B. The effects of treatments with chemical pesticides

Itisessentialtorememberthatallsyntheticfungicidetreatmentsincreasetotal nitrogen levels in the plant being treated. There are, however, greatdifferencesintheaminoacidswhenanalysedseparately(Symposiumoninte-gratedpestcontrolinorchards,Boulogne,1972.)Aswesawabove,nitrogenworks inbalancewithboron.Whathappensat the levelof the soilmightequallywell beproducedas a resultof repeated treatmentswith chemicalpesticides,whicharealmostallnitrogenous.So,onemightaskwhetherthesefrequentborondeficienciesingrapevinesandfruittreesariseasaresultofvariouschemicalpesticides.


Itisalsoimportanttorecordthatthenitrogencontentoftheleavesvarieswidely,accordingtothewaythenitrogenisused.Soenen(1975)notes, inregardtothepercentageofNindrymatter:

• ‘intensive’use:2.44%N• ‘random’use:1.9%N

Theauthorattributesthesedifferencestotheeffectofthepesticides.Thisconfirmswhatwesuggestedabove.LefterandPascu(1970)establishedthatthedegreeofthefruitscabattackisproportionaltotheratio:N%/K2O%.Sucharelationshipwouldseemtojustifycertainpracticesinthecontroloffruitscab,whoseactioncanonlybetheresultofnutritionaleffects.

4. Nutritional treatments against fruit scab

Potassiumisfrequentlyfoundintheformulationsrecommendedtocontrolfruitscab.DemestjevaandSturna(1970)reportgoodresultsfromtheuseofpotassiumchlorideasaleafspray(sixsprayingsduringtheseason).

Apartfromsulphurandcopper(whichcanbeconsideredasnutritionalchemicals and are officially confirmed to act against fruit scab certainpopular products employ amixture of sulphur and potassium carbonate,as generally used inGermany. Potassium permanganate, which is rich inmanganese,isalsoused.

Ofcourse,potassiumplaysafundamentalroleinproteinsynthesis.ThisisshownbythefactthateveryKdeficiencycausesagrowthofliquidexudateintheplantthatoccursfollowingproteinhydrolysis,withanaccumulationofaminoacids,especiallyasparagine.Thisisanaminoacidwhichisrecog-nised,aswehaveseenabove,tobethepreferredfoodofVenturia inoequalisandofanumberofotherpathogenicfungi.

Optimumprotein synthesis, as shown in research carried out on appleandpear trees,hascertain requirements. It is essential toguardagainstKdeficiency, but Kmust be present in balance with calcium, which is alsoindispensable.CraneandStewart(1962),workingonMentha piperita,wereabletoestablisheffectivelythataK/CaratiowhereCaisdominantencour-agesaphysiologicalstatewithdominantproteolysis,whiletheoppositeisthecaseifpotassiumisthedominantelement.

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Inthefirstcaseasparagineispresentingreaterquantities,whichshouldinprincipleencourageattacksoffruitscab.Inthesecondcase,however,theopposite is true: theplant ispredominantly ina stateofprotein synthesiswithahighglutaminecontent(Fig.2).

WedonothavethefigurestoallowustopositarelationshipbetweentheK/Caratioandtheresistanceof theplantto fruitscab.However,wehaveoneindication.Forexample,accordingtoSoenen(1976),theoptimumK/Caratiointheappletreeis1.20.(Soenendoesnotspecifytowhatextentthisratiowouldleadtoresistancetofruitscab.

As forboron,wedonothaveatourdisposal, for themoment, a singlereferencetoitsroleinrelationtofruitscab.Itisextremelylikely,however,that itplaysan important role, to theextent that (aswehaveseen) it isadirectfactorinproteinsynthesis.

Certaingoodeffectsofzinc-basedfungicidesmayquitelikelybeduetotheenrichmentinzincofthetissuesoftheplantstreatedwiththem.Ithasbeenestablished thateverydeficiency inzinc leadsconversely toan increaseofaminoacidsinthetissues,especiallyofasparagine.

VII. The immunity of the plant achieved by nutritional treatments

First, it is important todefinewhatweunderstandby the term ‘immu-nity’.Aswehaveemphasizedabove,certainfactorsaffectproteinsynthesis,causingtheplanttoshowresistance.Yeteveniftheplantappearstobe‘genet-ically’resistant,thiscannotbethecaseforthewholeofitsannualcycle.Theimportantthingisthattheplantisresistantatthestageof‘sensitiveperiods,’especiallyatthemomentofflowering.

Moreover,wehaveseenthatdifferentfactorsgoverningtheplant’senvi-ronmentmayserve,asitwere,to‘erase’resistance.Aharmfulinfluencemayoftenbeexertedbychemicalpesticides.Soitseemsthatsuchaninhibitionofproteinsynthesis(towhichweattributethesensitisationoftheplanttoitsparasites)mayhaveadeficiencyasitsimmediatecause.Thisdeficiencyistheresultofan‘inhibition’inducedbythepesticide,possiblythroughrepeatedapplicationstotheleavesortothesoil.Inbothcases,theoutcomeismalnu-tritionintheplant.


Toxicityandmalnutritioncouldbe(accordingtoVago)thetwofactorsattheoriginofdiseases,especiallyviraldiseases,duetothemetabolicproblemsthattheyengender(Chapters5and6).

Thisisthereasonwhy,inthethirdsectionofthischapter,wegaveexamplesofthedifferenceinlevelsofvariouselementsfoundinthetissuesofhealthytomatoesandthosebadlyinfectedwithaviraldisease.Itissignificantthatvariousdeficienciesarerecorded,ofCa,Mn,andCu-deficienciesthatarenottheconsequencebutthecauseofthedisease.

If,aswebelievewehavedemonstratedabove,deficiency=metabolicprob-lems=disease(that is tosay,parasitism), itwouldbenormaltoregisteraremissionofthediseasetotheextentthatweareabletocorrecteverypossibledeficiency.Itisatthispointthatwecanseetheextentofourignorance.Wedonotknow,forexample,howtocorrectmicronutrientdeficiencies,sincewearestillquitefarfromknowingallthepropertiesoftheseelements,ortheexactmannerinwhichthedeficienciesaremanifested.

In order to proceed further,we have to await further progress in plantphysiology.However,whatwealreadyknowshouldenableustoavoidtheworstmistakes and even to have a positive effect on the resistance of theplant.Often,intheuseofchemicals,weaimattheparasitebutitistheplantwhichisdamaged.

Synergies in micronutrients

While copper and sulphur seem toworkwell, use of these elements inisolationmaynotbethebestwaytoachievenutritionformaximumresist-ance.Manyothermicronutrientsmayalsoplayapart.

WelearnfromD.Bertrand,forexample,thatthefullrangeofpropertiesofboronisonlymanifestedinthepresenceofmagnesium,manganese,andmolybdenum. In the samewaywe see how copper andmanganese worktogetherinthegrowthofwheat(PilandandWillis,1937)orintheresistanceofricetoPiricularia(Primavesietal.,1972).

Another example of ‘synergism’ and its practical results, comes fromDufrenoy(1930).Ashepointsout,‘Withasolutioncontaining26elements,Hoagland andSnyder obtain strawberrieswhich aremuchmore vigorousandmore resistant toOidium and red spidermites than with a solutioncontainingonly12elements.’

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Allthisinthemeantimejustifiesthelogicofusingmicronutrientcomplexes,alliedwiththemajorelements.Thisformsthebasisofoursuggestionsforcontrollingfruitscab.

The balance: KCaMg

WedrawheremainlyontheworkofCraneandSteward(1962)concerningtheK/Caratioinrelationtothelevelofproteinsynthesis.Fortherest,werelyontheresultsobtainedforthedeclineofvariousparasitesthroughbetterpotassiumnutrition,aswehaveseenabove.

Calcium is also a fundamental element for the plant’s nutrition. Shear(1975) lists no less than 30 afflictions or diseases that arise as a result ofcalcium deficiency. Calcium andmagnesium are very closely related. Forexample,Shear(op. cit.)notesthatifMglevelsareincreasedtoasufficientdegree,thelevelofabsorptionofCaalsorises.Thisexplainsthegoodresultsobtainedintacklingdiseasesinvolving‘necroses,’and‘blackheart,’or‘blackrot.’Atthemoment,‘blackrot’inchicoryandnecrosisintheterminalbudsof chard grown under glass can be controlled by treatments based on acombinationofCa,Mg,andB.

In the same way, ‘proliferation’ in apple trees, which is attributed tothemultiplicationof amycoplasma, isonly secondaryandcanbe treatedeffectivelybyaspecialcombinationofCo,Cu,andMn.Thisisquitelogical,bearinginmindthatcalciumdeficiencies,whetherspontaneousorasaresultof boron deficiency, are oftenmanifested in shrinking internodes knownas ‘witches’brooms’onthetreesor incrinkly leaves.KandCaarecloselylinked:Cadeficiency causes liquefactionof themiddle lamella of the cellwall,becauseoflackofpotassiumpectate.ThisiswhatmakestheK/Caratioimportant.

Chieflyby correcting this ratio in favourofpotassium,wewere able tocontrol scale in citrus trees, asVaithilingam (1982)managed to eliminateparasiticinsectsfromrice(p.206).

Treatments with micronutrients

Followinghisstudiesofdiseasesof thecitrusandregardingdeficienciesandtheirpathologicaleffects,Dufrenoyexpandedonotherdiseases,exper-imentingwithvariousmicronutrientsandespeciallywithzinc.Itwasfoundthatthenumberofenzymescontainingzincasacomponentwasveryhigh.


This explains thehistologicalmodifications brought about by the func-tional problems of enzyme chains. He drew attention to the use of zincsulphateingrapevinesagainst‘fanleaf’or‘infectiousdegenerationofgrapes’(Dufrenoy,1934).

Henotes: ‘From thepoint atwhich thebudsburst, the vinedevelopedbranch tendrils with longer internodes than in the ‘fanleaf’ vines. Then,on24July,measurementsconfirmedthatthiselongationofthemerithalleswasaccompaniedbyabundantfructification.’Weknowthatzincdeficiency,especiallyintomatoes,causesproteinsynthesistobeinhibited,andthatthiscoincideswithanincreaseinaminoacids.Significantlythereisaconsider-ableaccumulationofasparagine,anitratefoodstuffwhich,aswehaveseen,isessentialforpathogenicfungi(KrisnaChutima,1963).

Asforboron,werecall thatapplicationsof thiselement,whethertothesoilorasaleaftreatment,provedtobeeffectiveagainstanumberofdiseases.Thus,bycorrectingborondeficiencyinbeet,itispossibletoeliminatePhoma betae.Inthesameway,silverleafdiseasecanbecontrolledingrapevines.

Inthecaseofpeachblightravagingtreesthatareshrivellinginanenvi-ronmenttoohumidforthem,DufrenoyandBruneteau(1937)showedthatthosetreestreatedwithaboronsaltre-establishthemselvesveryquickly.

Similarly,thetrialsofBranasandBernon(1954)showedthatgrapevinesattackedwithshrivellingbysilverleafdisease[Stereum purpureum]reestab-lishthemselveswhenborontreatmentsareappliedtoboththeleavesandthesoil.Thisisnotreallysurprising,giventheimportanceofboronintheplant’sphysiology,aswehaveseenabove.

Thesefindingslendweighttothehypothesisthatborondeficiencyliesatthe bottomof a large number of diseases, especially viral diseases. Aswehaveemphasized,thesymptomsofviraldiseasesresemblethosearisingfromborondeficiency.Thiswouldseemtobefurtherprovedbytheexampleof‘apricotvirula.’AsPenaandAyusoobserve,‘Asaconsequenceofthesymp-toms,thedevelopmentofthedisease,andthe result of analyses of the leaves,theborondeficiencyhypothesiscouldbeadvanced’(PenaandAyuso,1970).

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Wemustalsoprobablyplacethe‘declines’inthesamecategoryofideas:inotherwords,thevarioustypesofwitheringseeninfruittrees,forexample,pearsandapples.Campbell(1970)wasable toobtaingoodrecoveryratesinpeartreessufferingfrom‘appledecline’thankstocopperandzincbasedsprays, after he discovered a number of ‘latent’ viruses in the trees. Thiswouldseemtoconfirmouropinionthatalldiseases,includingviraldiseases,arelinkedtometabolicproblemsthatareinturnoftenlinkedtodeficiencies.

Finally, the ‘complex’ disease that attacks certain species of Prunus intheMolières region inTarn, seems also tobe the result of oneor severaldeficiencies. One thing is certain: the existence of a pathogenic agent, amycoplasma,hasalsobeensuspectedhere.Theexistenceofthisorganismhasbeenshownconvincinglyintheinfectedhostplant.But,asresearchersrecognise(Bernhardetal.,1977),thepathogenicityofthismycoplasmaisfarfromobvious.Yetagainwearefacedwiththesamequestion:causeoreffect?Asfarasweareconcerned,thisquestionstillcallsforthesameresponse:itis thedeficientnutritionof theplant that leads to its susceptibility,due toinhibitionof protein synthesis. (Research is currently inprocess todeter-mine,asfaraspossible,thefactorsthatareresponsible:rootstock,variety,feedingwithmajor elements,micronutrients, etc.Onemight add that allthesefactorsrelatetothenutritionoftheplant.)

Finally, we recall that numerous authors have deliberately tried usingmicronutrientsagainstdiseases,withanindirecteffectonthenutritionoftheplanttheyaretryingtoprotect.Mudich(1967)showedthat,unlikeCu,Zn,andMn,molybdenumcausedadecreaseinthesusceptibilityofpotatoestomildew.However,thissameauthorquotesGalilov,accordingtowhompotatodiseasescanbecontrolledwithsomelevelofsuccessbytheuseofvariousmicronutrientssuchasCu,Mn,B,andZn.Wethinkthatthedifferencesintheseresultsmayarisefromdifferences,tostartwith,inthecompositionofthesoil,andespeciallyfromanylaterdeficiencies.

The research of Prusa (1965) into the effects of variousmicronutrientsonleafrollinhopsalsoproducedinterestingresults.Theauthorestablishedthatthediseasewasviralincharacter,andemphasisedthecloserelationshipbetweentheexternalmanifestationsofthediseaseinotherwords,thesymp-tomsandthenutritionalconditions.

In the field, the disease was controlled by applications of various saltsbasedonmicronutrients,especiallythosewithabaseofboron,magne-sium,manganese,nickel,iodine,andzinc.


ThisledtothediseasebeingcontrolledinGermanybyzincbasedprepa-rations,whetherintheformofsulphateorzineb.Still,weshouldpointoutequallysignificanteffectsasthoseachievedwithzincmaybeobtainedwiththeuseofboronormagnesium.Analysis shows thatdiseasedplantshaverelativelylowlevelsofthesetwoelements.

Ontheotherhand,onefactunderlinesclearlytheindirect natureoftheseeffects:copper-based products aggravate the disease rather than combating it.

Weshouldalsopauseamomenttolookatanotherprocedureofindirectpest control,byanactionbeneficial for themetabolismof theplant.Thisis an elegantprocedure,which consists of soaking seeds inmicronutrientsolutions.

Polyakov(1971)triedthefollowing:Cu,Mn,Co,andBagainstSclerotiniaorgreymouldinsunflowers.Hismethodwastosoaktheseedsbeforesowingthem.Inpractice,seedsweresoakedfor10hoursinsaltsolutionsof0.1%.Twolitresofsolutionaresufficienttosoakalltheseedsneededtoplantonehectare.

Theseexperimentsshowacleardecline,accordingtotheevidence,withdifferentmicronutrients(Table17).

Table 17: Percentage of attacks on sunflowers by Sclerotinia according to the micronutri-ents used to soak the seeds (averaged over 4 years)

Controls Manganese Cobalt Boron Copper

16.3 4.4 4.9 6.4 7.7

As can be seen, cobalt and manganese have shown the best results.However, one wonders, after what we have already seen above regardingsynergeticeffects,whethercertain‘complexes’ofmicronutrientsmightnothavebeenstillmoreeffective. Interestingresearchcouldbeundertaken inthisdirection.

Polyakov’s experiments (which note in passing that ‘microelements’improve resistance tonumerousdiseases) also includedananalysisof theleaves.Itwasshownthatthroughtheactionofthemicronutrientsonemaybringaboutadeclineinreducingsugars.

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Theauthorobservedthatthisphenomenonistheconsequenceofarefluxtowards the reproductive organs, and of rapid transformation of simplesugarsintoreservenutritionalsubstances.Asaresultthedevelopmentofthepathogenicfungusisinhibited,sinceitnolongerhasthesolublesugarsoftheplantcellsatitsdisposal.

Theoutcomeisanexplicationthatcoincidescompletelywithourtheoryoftrophobiosis.Polyakovwrites,‘Thetreatmentofplantswithmicronutrientsintensifiesthephysiologicalprocessesandthuscausesthepathogenicagenttobeinhibitedordestroyed,ashappenswithvarietieswhicharenaturallyimmune.’

205 General Conclusions

General Conclusions

Itisuniversallyrecognisedthatthehealthofourcropsisdeclining.Thereisaseriousproliferationofparasitesanddisease,inspiteoftheuseofpowerfulchemicalpesticides,Infactitispreciselythesechemicalpesticidesthatcausetheproblem.Atlonglastithasbeenadmittedthattheyhave‘repercussions,’otherwisecalled‘sideeffects.’Inotherwords,theirusecausesotherproblemstoflareup,intheshapeofrapidproliferationofpestsorthedevelopmentofdiseases(fungal,bacterial,andviral)-nottomentiontheappearanceofneworganismsrecentlyidentifiedasmycoplasmas,spiroplasmas,or‘viroids.’

Inhumanandveterinarymedicinesuchphenomenahavebeen labelled‘iatrogenicillnesses.’Whenitcomestothehealthofplants,weshouldrecog-nise similar ‘failures’with equal clarity.These arenormally characterised,however, indifferentways,dependingonwhetherone isdealingwith therapidmultiplicationofaninsectormite,orwiththedevelopmentofapath-ogenicagentfromtheplantkingdom.Onespeaksof‘proliferation’whenatreatmentwithonepesticideoranotherisfollowedbyanincreaseinpopula-tionsofspidermites,aphids,orpsyllids.However,whenfungaldiseasesareraging,suchasOidiumorbotrytisingrapevinesorfruitscabinappletrees,therapidmultiplicationisexplainedasa‘resistance’ofthepathogenicagenttothefungicideinquestion.

Accordingtothetraditionalidea,ifthereisarapidmultiplicationofspidermitesoraphidsafteratreatmentwithparathionorcaptan,thesechemicalsaresaidtohavedestroyedtheirnaturalpredators.However,suchanexpla-nation does not apply to all ‘imbalances’ of this sort - for instance, rapidproliferations following treatments of the soil. It is even less useful whenlookingatthedevelopmentofcryptogamic,bacterial,orviraldiseases.Thisiswhy,asmentionedabove,adifferentexplanationisadvanced:a‘resistance’ofthepathogenicfungustothespecificfungicide.

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But to adopt suchan interpretation is to turnablind eye to a seriesofresultsobtainedinbothlaboratoryandfieldtests.Asweourselvesshowedinthecaseofspidermites,thepestsactuallyincreasedtheirbioticpotentialwhenfedonleavestreatedwiththesuspectchemical.Thereisanincreaseindailyrateofreproductionandlifeexpectancy,modificationofthegenderratioinfavourofthefemale,andshorteningoftheevolutionarycycle.Suchaprocess,alsofoundinaphids,explainstheirproliferation,whichisnutri-tionalinnature.

Suchphenomenaarenot,however,limitedtotheanimalworld.Ithasalsobeenshown,forexample,thatdithiocarbamatescausethedevelopmentofOidiumandBotrytiswhenusedtotreatgrapevinesformildew.(Chaboussou,1968,andVanevandCelebiev,1974).Themechanismisthereforethesameinbothcases,andfairlyeasytoproveaslongasonehasadequatecontrols.

Wethereforebelievewehaveestablishedafundamentalfact:namely,thatthe relationships between plant and parasite are primarily nutritional innature.Wehavegiventhename‘trophobiosis’tothistheory.

Wehaveshownthatsolublesubstancessuchasaminoacidsandreducingsugars cause the stimulationofbioticpotential inparasiticorganisms (forinstance,spidermites,aphids,bacteria,pathogenicfungi,andviruses)whichisexpressedasproliferationinthefield.Thesesubstances,whicharelocal-isedinthecellularvacuoleandinthevessels,formtherawmaterialsoftheproteins,withwhich they are in constant balance.We referred to variousauthors, in particular to the works of the eminent French biologist JeanDufrenoy.

Inthelastanalysis,then,theresistanceoftheplanttoitsdifferentparasitesdependsonthebalancebetweenproteinsynthesisandproteinbreakdown.Inotherwords,a predominance of protein breakdown increases the plant’s susceptibility.Thishappenswiththeuseof‘poisons’(whichiswhatchemicalpesticidesareforplants),especiallyinmultipleapplications.

Conversely,predominance of protein synthesis increases the plant’s resist-ance, or its ‘immunity.’This iswhathappenswith some ‘remedies,’whoseactiononaplant’smetabolismrenderitresistantthankstothebiochemicalstatecreated(at least foracertainperiod).Thisresistanceseemstocorre-spondtoagreatextenttothatfoundinvarietiesthatareresistant‘bynature,’thatis,genetically.


In thisnewdevelopmentofbacterial andviraldiseases, chemicalpesti-cides,especiallyforaggravatingthepoorhealthoffruittrees.Thisiswhywegavesomespacetotheissue.

It seems tousparticularly significant that aplantbacteriologist suchasourcolleagueRide(INRA), inhisresearchonthegrowing importanceofinfectionsofbacterialorigin,seesthesameconnection.Ashenotes,‘Thisspreadseemstooccurasaresultoftheincreaseintreatmentsmakinguseofsyntheticchemicals.’

It is obvious thatwehere encounter two factors atwork.Bothof theminterveneinthesameharmfulwayattheleveloftheplant’sphysiology:

• theabandoningofmineralproducts,suchascopperorzincproducts.• theadoptionofchemicalpesticides,especiallydithiocarbamates.

Whatmightatfirstappeartobeasimplesubstitutionofoneproductforanother actually has a doubly harmful impact on the plant.Minerals likecopperandzincgenerallyhaveabeneficialeffectontheplant’smetabolism,andthusonitsresistance.Chemicalproducts,ontheotherhand,havetheopposite effect, by inhibiting protein synthesis. The impact of these twoeffectsonthemetabolismoftheplantmakeitsusceptibletovariouspara-sites,especiallybacteria.

Moreovertheoldquestionaboutthenatureof therelationshipbetweenplantanddiseasehasstillnotyetfoundananswer.InthewordsofTrocmé:

‘We cannot exclude thepossibilityof relationshipsbetweendeficienciesandcertaindiseases,especiallybacterialandviraldiseases.Itmaybethatthese diseases encourage the manifestation of deficiencies, or that thedeficienciesencourage themanifestationof thesediseases.Forexample,treesdeficientinboronorzincmaybemoresusceptibletocertainviralorbacterialdiseases’(Trocmé,1964).

Webelievethatourtrophobiosis theorycouldfill thisgap.Aswesee it,thereisasequencethathasbeenclearlyproven,namely:

Deficiency inhibitionofprotein synthesisaccumulationof solublesubstancesimproved nutrition of parasitesrapid multiplication andvirulenceofbacteriaandviruses,etc.

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Italsoseemsvital to try toconfirmas soonaspossible therelationshipthatseemstoexistbetweentheuseofchemicalpesticidesandthetriggeringof deficiencies. Several works have raised this issue. As we have alreadymentioned, the overwhelmingmajority of chemical pesticides are nitrog-enousandoftenchlorinatedaswell.Thus the traditionalbalancebetweennitrogen andmicronutrients (especially boron and zinc)may be upset infavour of soluble nitrogen, because of a deficiency. This in turn creates asituationthatisunfavourablefortheplant’sresistance.

The theoryof trophobiosisalsoexplainswhysymptomscausedbydefi-ciencies coincidewith those caused by diseases.Official plant protection,however, assiduously casts doubt on this convergence, claiming that anycause-and-effectrelationshipisanillusion.

We are still a longway fromgrasping the extent and the gravity of theeffectsofchemicalpesticides.Thisappliesespeciallytomultipletreatmentsthatsomeresearchsuggestsmayhaveacumulativeeffect.

Forthesamereasons,chemicalfertilisersmaycausedeficiencies.Thesecanhaveextremelyseriousconsequencesfortheplant’smetabolism.Dufrenoy,forexample,hasshownthatborondeficiencyinbroadbeanscausesdisin-tegrationof thenucleusof thecell. Inconditions suchas this, it ishardlysurprisingthatviraldiseasesandotherdiseasesoftherootcandevelop,quitepossiblyasaresultofthecumulativeuseofherbicides.

Viral diseases appear to differ very little from other diseases in theirreactionstoenvironmentalfactorsortocontaminationoftheplant.Inotherwords,justaswithotherdiseases,itisthebiochemicalstateoftheplantthatgenerallydetermineshowsusceptibleitwillbe.

InthisconnectionwegaveabriefsummaryoftheworkofVago,inrelationto the effects of the environment on the development of viral diseases ininsects.It seems that, in both animals and plants, susceptibility to disease is the result of metabolic problems.

Furthermore,theseproblemsthemselvesmayappearasaresultofmalnu-tritionor toxic effects. Suchaprocess seems to stemquiteoften from theeffectsofchemicalpesticides.Thismayoccurthroughdirectactionontheplantatthetimeofapplication(especiallyofherbicides),whicharescatteredso liberallywithnoconcern for the lifeofsoilmicroorganisms.Or itmayoccurthroughtheimpactofchemicalfertilisersandthedeficienciestheycancause,whichinturnaffecttheassimilationandnutritionoftheplant.


Itisnoaccidentthat,inexploringtheseissuesofresistanceandprotectionoftheplant,wefindourselvesface-to-facewiththephenomenonofnutri-tion.AtthispointitisperhapsrelevanttorecalltheworkofBodenheimer(1955),whodisputestheDarwiniantheoryabouttheregulationofanimalpopulationsbypredatorsandparasites.Bodenheimerstressesthatthisneverpreventsproliferationintheenvironment.Instead,Bodenheimeremphasizestheimportanceforpopulationlevelsofthequalityofthedietas‘thesourceofanimalenergy’.

Forexample,fluctuationsinvolepopulationsdonotnecessarilyconformto the level of predators, but can be explained, he says, by differences inlevelsoffertility.Thesedifferencesmaythemselvesbesubjecttoanindirectseasonal influence on the quality of the diet. Bodenheimer alsomentionsthevoles’ingestionofcertaingonadotrophicsubstancesproducedincertainseasonsandinvaryingquantities.

In addition, according to Maurice Rose and Jore d’Arces (1957), thenutritionoforganisms,viadeficiencies,hasplayedafundamentalroleintheprocessofevolutionitself.

Toconclude:atheoryonlyacquiresvaluethroughtheresultsitprovides.Inthisrespect,wecanalreadysaythattheresultssofarobtainedconcerningtheprotectionofvariousplantsfromdifferentdiseasesservetoconfirmourideasandencourageustocontinuealongthispath.Theseresultsarebasedonachievingwell-balancedfertilisationandstimulationofproteinsynthesisthroughtheuseofcomplexesofmicronutrients.

First,weneedtoovercometheideaof‘thebattle’:thatis,wemustnottrytoannihilatetheparasitewithtoxinsthathavebeenshowntohaveharmfuleffectsontheplant,yieldingtheoppositeeffecttotheonedesired.Weneed,instead,tostimulateresistancebydissuadingtheparasitefromattacking.

This implies a revolution in attitude, followedby a complete change inthenatureofresearch.Workonplantphysiologyanditsrelationshiptotheresistanceoftheplantwouldbeparticularlyimportant.Inotherwords,weneedadeeperunderstandingoftherelationshipbetweenthe‘conditioningoftheplant’andproliferationoftheparasite.

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THIS BOOK CALLS INTO QUESTION THE CENTRAL ARGUMENTS OF INDUSTRIAL AGRICULTURE, sets out the theoretical foundation for ecological agriculture and quietly calls for a revolution. Based on his own research and that of others, Francis Chaboussou argues that we should improve the health of our crops rather than using chemicals to eliminate pests and diseases, because healthy crops resist attack. Furthermore, chemical pesticides and fertilisers weaken plants, making them vulnerable to disease.

Chaboussou says: ‘... we need to overcome the idea of the ‘the battle’: that is, we must not try to annihiliate the parasite with toxins that have been shown to have harmful effects on the plant, yielding the opposite effect to the one desired. We need, instead, to stimulate resistance by dissuading the parasite from attacking. This implies a revolution in attitude, followed by a complete change in the nature of research. Work on plant physiology and its relationship to the resistance of the plant would be particularly important.’

As farming becomes more intensive and GM crops are prmoted as another narrow ‘techno-fix’, Chaboussou’s book reminds us that there are genuine alternatives to the chemical treadmill. The questions he raises about the impact of chemical pesticides and fertilisers on the health of plants urgently need to be investigated with new research.

‘For me this is one of the most important books ever written on theoretical agriculture, as important as Albert Howard’s Agricultural Testament.’EDWARDGOLDSMITH

‘Almost all conventional chemical agricultural technologies create favourable conditions for the growth of pest and disease organisms: this book shows that much of the problem can be explained through increases in soluble nitrogen, amino-acid and sugar concentrations in the plant cells.’DRULRICHLOENING

‘A very important reference book... every agronomist should have it on his desk.’JOSÉLUTZENBERGER

‘Although the ways in which synthetic fertilisers and pesticides affect plant physiology are not yet fully understood, Chaboussou’s Theory of Trophobiosis gives a clear approach for how to deal with such problems in practice. learning how to treat the sick and not the sickness is an effective tool for plant protection, substantially reducing problems with pests and diseases in the field, especially for those working in agriculture without chemicals.’MARIAJOSÉGUAZZELLI

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