biological control joyce e. loper research plant pathologist, usda-agricultural research service...

Biological control

Joyce E. Loper

Research Plant Pathologist, USDA-Agricultural Research Service

Professor (courtesy), Department of Botany and Plant Pathology

[email protected]

738-4057

mailto:[email protected]

The Plant Disease Triangle

Path

ogen H

ost

Environment

Take home message: Microorganisms, whether indigenous or introduced are an important component of the environment.

Biological control

Reduction of the amount of inoculum or disease-producing activity of a

pathogen accomplished by or through one or more organisms

other than humans.

Biological control gained strength as a subdiscipline of Plant Pathology in the 1960s, when a group of scientists recognized that epidemics of soilborne plant diseases could not be understood without considering the the ecology of soil fungi and Oomycetes and the resident soil microflora.

Biological Control of Plant Diseases

Kinds of Biological Control

• Conservation- cultural practicesConservation- cultural practices Suppressive soilsSuppressive soils

General suppressionGeneral suppression

Specific suppressionSpecific suppression• ClassicalClassical – self sustaining following a single release of a “natural enemy”

• AugmentativeAugmentative – periodic introduction to supplement natural reproduction Chestnut Blight and hypovirulenceChestnut Blight and hypovirulence

• InnudativeInnudative – mass introduction of biocontrol agent Crown gallCrown gall Heterobasion Heterobasion root rotroot rot Fire blightFire blight Postharvest diseasesPostharvest diseases

Suppressive Soils

• The pathogen does not establish or persist

• The pathogen establishes but causes little or no disease

General Suppression

A fixed level of the pathogen causes less disease in the presence of indigenous soil organisms.

Propagule level

Dis

ease

sev

erit

y

field soilsterilized soil

Take all of wheat caused by Gaeumannomyces graminis var tritici

Take-all decline with monoculture of wheat

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Years of Monoculture

Disease severity

Associating populations of organisms with soil suppression

Pseudomonas fluorescens produces an antibiotic that is toxic to the take-all pathogen

The antibiotic 2-4-diacetylphloroglucinol

is toxic to the take-all pathogen

CH3 CH3

OHOH

OHO O

No seed treatment Seed treatment with P.f.

Wheat seed treatment with Pseudomonas fluorescens for control of take-all

Seed treatment with mutant that does not produce an antibiotic

Borneman and Becker evaluated theMicroorganisms associated with cysts in suppressive and conducive soils

Associating populations of organisms with soil suppression

Olatinwo, R., Borneman, J., and Becker, J. O. 2006. Induction of beetcystnematode suppressiveness by the fungi Dactylella oviparasitica andFusarium oxysporum in field microplots. Phytopathology 96:855-859.



General suppressionGeneral suppressionSpecific suppressionSpecific suppression

• ClassicalClassical – self sustaining following a single release of a “natural enemy”

• AugmentativeAugmentative – periodic introduction to supplement natural reproduction

InnudativeInnudative – mass introduction of biocontrol agent Crown gallCrown gall Heterobasion Heterobasion root rotroot rot Fire blightFire blight Postharvest diseasesPostharvest diseases

Chestnut Blight Chestnut Blight and hypovirulenceand hypovirulence

Biological control with Introduced Antagonists

Biological control agent:

Hypovirulent isolates of Cryphonectria parasitica

Disease: Chestnut Blight

Pathogen: Cryphonectria parasitica

Mechanism: hypovirulence

History of the Chestnut Blight Pathogen in the United States

Transmission of hypovirulence decreases with diversity of vegetative compatibility groups in the pathogen population






• InnudativeInnudative – mass introduction of biocontrol agent

Crown gallCrown gall Heterobasion Heterobasion root rotroot rot Fire blightFire blight Postharvest diseasesPostharvest diseases

Biological control with Introduced Antagonists

Biological control agent:

Agrobacterium radiobacter

Disease: Crown gall

Pathogen: Agrobacterium tumefaciens

Mechanism: antibiosis

Crown gall caused by

Agrobacterium tumefaciens

Infection byAgrobacteriumtumefaciens

Short period ofSusceptibility:Wound typicallyheals over after about 24 hours andis no longer an opening for infection

In nurseries growing woody perennials, wounds are inducedby root pruning. These can betreated with the biocontrol agent immediately

Treated with K84 Untreated

Why does biological control of crown gall work so well???

•Limited time of host susceptibility to disease This means the biocontrol agent doesn’t have to persist for a long time in the environment

•The infection court is defined and easily treatedThis means the biocontrol agent can be applied directly to the infection court, and doesn’tHave to move there on its own

•There are no chemical controls available •The sensitivity of the pathogen population can be predicted

For example, strains pathogenic to cherry are sensitive to agrocin 84, whereas strains pathogenic to apple are not uniformly sensitive.


• Conservation-Conservation- Suppressive soilsSuppressive soils




• InnudativeInnudative – mass introduction of biocontrol agent Crown gallCrown gall

Heterobasion Heterobasion root rotroot rot Fire blightFire blight Postharvest diseasesPostharvest diseases

Heterobasidion root rot of pine

•The fungus Heterobasidion annosum is the most damaging root pathogen of coniferous trees in the Northern hemisphere.• It progresses from the roots into the base of a tree, causing an economically important butt rot. •Once established in a site, the fungus is almost impossible to eradicate; it spreads progressively by contact of healthy roots with infected roots

http://www.biology.ed.ac.uk/research/groups/jdeacon/microbes/heterob.htm

•Fruiting bodies release air-borne basidiospores that can spread the infection to new sites. •Basidiospores land on freshly cut stump surfaces, and the fungus grows down through the stump tissues to the dead roots, from which it can infect the roots of adjacent healthy trees.


•Fresh pine stumps can be colonised by another fungus, Phlebiopsis gigantea (previously called Peniophora gigantea), which is weakly parasitic but poses no danger to healthy trees. •If Phlebiopsis is applied first then it can prevent invasion by H. annosum, protecting the stump surfaces without the need for phytotoxic chemicals. •P. gigantea is commercially available in Britain, Sweden, Norway, Switzerland and Finland, as either a spore suspension or a dry product (named "Rotstop"). •It was available in the USA until 1995 when the Environmental Protection Agency required it to be registered officially as a biological pesticide - a relatively expensive process that probably would not be cost-effective for the commercial producers.

http://www.biology.ed.ac.uk/research/groups/jdeacon/microbes/heterob.htmhttp://www.nysaes.cornell.edu/ent/biocontrol/pathogens/p_gigantea.html



• Conservation-Conservation- Suppressive soilsSuppressive soils




• InnudativeInnudative – mass introduction of biocontrol agent Crown gallCrown gall Heterobasion Heterobasion root rotroot rot Fire blightFire blight

Postharvest diseasesPostharvest diseases

Decay management productDecay management product

for for • CitrusCitrus• Stone fruitsStone fruits• Pome fruitsPome fruits• PotatoesPotatoes

a.i.: Pseudomonas syringaea.i.: Pseudomonas syringae - ESC-10: EcoScience strain- ESC-10: EcoScience strain - ESC-11: USDA strain- ESC-11: USDA strain

Bio-Save

untreated

Why PostharvestWhy Postharvest Biocontrol?Biocontrol?

• Market needMarket need::

– few labeled chemicalsfew labeled chemicals

– fungicide resistance problemfungicide resistance problem

• System characteristicsSystem characteristics

bin dump

chlorine spray

Chlorine bath or sprayChlorine bath or spray

Clean Rinse or Fungicide SprayClean Rinse or Fungicide Spray

fungicide in wax

Wax applicationWax application

Bio-SaveBio-Save Application Application

Usage History of Bio-Save by CropUsage History of Bio-Save by Crop

00

1,000,0001,000,000

2,000,0002,000,000

3,000,0003,000,000

4,000,0004,000,000

5,000,0005,000,000

Ca

rto

ns

Ca

rto

ns

CitrusCitrus

00

1,000,0001,000,000

2,000,0002,000,000

3,000,0003,000,000

4,000,0004,000,000

19991999 20002000 20012001 20022002 20032003 20042004 20052005

Sa

cks

Sa

cks

PotatoPotato

00

2,000,0002,000,000

4,000,0004,000,000

6,000,0006,000,000

8,000,0008,000,000

19991999 20002000 20012001 20022002 20032003 20042004 20052005

Lug

sL

ugs

CherryCherry

00

2,000,0002,000,000

4,000,0004,000,000

6,000,0006,000,000

8,000,0008,000,000

10,000,00010,000,000

Ca

rto

ns

Ca

rto

ns

Pear and ApplePear and Apple

From Stockwell and Slack. Phytopathology 97: 244-249.

The Plant Disease Triangle

Path

ogen H

ost

Environment

Take home message: Microorganisms, whether indigenous or introduced are an important component of the environment.

biological control joyce e. loper research plant pathologist, usda-agricultural research service...

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