Fungal Fungal relationships relationships with plantswith plantsObligate and facultative Obligate and facultative parasitism/pathogenicityparasitism/pathogenicity
Why is plant pathology Why is plant pathology important?important?
Food quantityFood quantity Food qualityFood quality Agrinomic practices – tillage, Agrinomic practices – tillage,
pesticide usepesticide use Diversity and stability of ecosystemsDiversity and stability of ecosystems BeautyBeauty
Better understanding of Better understanding of disease processes – disease processes –
examples of useexamples of use Disease control through life cycle Disease control through life cycle
managementmanagement Puccinia graminis triticiPuccinia graminis tritici on wheat and on wheat and
barberrybarberry Orchard management practice in Orchard management practice in Venturia Venturia
inaequalisinaequalis Optimizing pesticide applicationOptimizing pesticide application
Disease forecastingDisease forecasting Pesticide designPesticide design Breeding for resistanceBreeding for resistance
Fungal pathogenicity on Fungal pathogenicity on plantsplants
Plant pathogens can be biotrophic Plant pathogens can be biotrophic (rusts and smuts) or (rusts and smuts) or hemibiotrophic/necrotrophic hemibiotrophic/necrotrophic (opportunistic)(opportunistic)
Necrotrophs can display high levels Necrotrophs can display high levels of host specificity, e. g. of host specificity, e. g. Magnaporthe Magnaporthe griseagrisea
Saprotroph“Weak”Facultative parasite
Necrotroph“Strong”Facultative parasite
BiotrophObligate parasite
Increasing specialization Increasing host range
Symptom types -- Symptom types -- necrosisnecrosis
Blumeriella on plum Alternaria solani – early blight of potato
Symptom types – wiltSymptom types – wilt
Ophiostoma novo-ulmi
Panama disease: Fusarium oxysporum f.sp. cubense
Symptom types – hormone Symptom types – hormone inducedinduced
Taphrina deformans
Hypertrophy Hypertrophy auxin
Synchytrium endobioticum
http://www.maff.gov.uk/planth/pestnote/pwd.htm
Symptom types – hormone Symptom types – hormone inducedinduced
Fusarium moniliforme = Gibberella fujikuroi gibberellins
EtiolationBakanae of rice
Symptom types – Symptom types – sterilization sterilization
Claviceps purpurea – ergot
Ustilago maydis
Obligate parasites – e. g. Uredinales
Rust fungi may have as many as five different spore-producing stages in their life cycles
Heteroecism – e.g. wheat stem rust- two taxonomically different host plants in order to
complete life cycle- ‘alternate’ host: stages (haploid)- primary host: stages (diploid)
Autoecism – e.g. bean rust- entire life cycle completed on a single host species
Microcyclic rusts ≤ 3 spore types
spermatia (n)insect transportedto receptive hyphae (n)heterothallic
aecia on barberry(n+n)
aeciospores(n+n)airborne
SUMMERurediniospores(n+n)airborne
FALL
uredinia on grassfrom infection byaeciospores orurediniospores
telia on grass
teliospore on straw(n+n)
WINTER
karyogamy(2n)
meiosis
teliospore (2n)germinating onstraw withpromycelium and basidiospores (n)
SPRING
basidiospore(n)airborne
spermagonia on barberry frominfection by basidiospores
Life Cycle of Puccinia graminis
IV
I
O
II
III
Puccinia graminisPuccinia graminis f.sp. f.sp. triticitritici life cycle life cycle
host ploidyOverwintering and transport of urediospores
Stage IV Basidia bearing basidiospores (n)
• in the spring teliospore germinates a promycelium• diploid nucleus migrates into the promycelium and
undergoes meiosis• four haploid nuclei migrate into developing sterigmata
& are incorporated into basidiospores• basidiospores reinfect alternate host
teliospore germinates, gives rise to a short germ tube of determinate growth known as the promycelium.
Promycelium: site of meiosis & formation of sterigmata and basidiospores
Stage 0: Spermogonia bearing spermatia (n) and receptive hyphae (n)
• fertilization of the receptive hyphae by spermatia initiates the dikaryon and the formation of aecia
Stage 0 and I produced on “alternate” host
helios.bto.ed.ac.uk/bto/microbes/biotroph.htm
Stage II: Uredinia bearing urediniospores (n+n)
• reinfect primary host• amplifies disease within primary host• uredinia can eventually develop into telia
helios.bto.ed.ac.uk/bto/microbes/biotroph.htm
Teliospore: site of karyogamytechnically part of the basidium
Stage III: Telia bearing teliospores (n+n2n)
• final stage on primary host• overwinters as dikaryon
Facultative parasitismFacultative parasitism: : Magnaporthe griseaMagnaporthe grisea
infectioninfection
Magnaporthe griseaMagnaporthe grisea / / Oryza Oryza sativasativa
Some non pathogenic M. grisea strains can grow in host plants if wound inoculated
Host resistance and basic Host resistance and basic compatibilitycompatibility
Most plants are not attacked by the Most plants are not attacked by the vast majority of potential pathogensvast majority of potential pathogens
Preformed defensesPreformed defenses Potential pathogens secrete Potential pathogens secrete
chemicals during growth that can be chemicals during growth that can be detected detected
What is a pathogenicity What is a pathogenicity gene?gene?
A gene whose product contributes to A gene whose product contributes to successful fungal establishment in successful fungal establishment in the hostthe host
ExamplesExamples Hydrolytic enzymes (especially for Hydrolytic enzymes (especially for
necrotrophs)necrotrophs) Compatibility determinants (especially Compatibility determinants (especially
for biotrophs)for biotrophs) Defense avoidance/detoxificationDefense avoidance/detoxification
What is a resistance What is a resistance gene?gene?
A gene whose product enables the A gene whose product enables the host to detect a pathogen and/or host to detect a pathogen and/or mount a defensemount a defense
The fungal product that is detected The fungal product that is detected does not have to be directly involved in does not have to be directly involved in
pathogenesispathogenesis is defined as being produced by an is defined as being produced by an
avirulence geneavirulence gene
Fungal pathogenicity on Fungal pathogenicity on plantsplants
Fungal pathogens of plants include Fungal pathogens of plants include opportunists, necrotrophs and biotrophsopportunists, necrotrophs and biotrophs
Resistance is seen at several levels Resistance is seen at several levels Non-host resistance – Non-host resistance –
Widespread, early onset, effective Widespread, early onset, effective Passive – attachment/germinationPassive – attachment/germination Active – initial colonization, e. g. wall Active – initial colonization, e. g. wall
appositionapposition HypersensitivityHypersensitivity
DurableDurable
Varietal resistanceVarietal resistance
Superimposed on basic compatibilitySuperimposed on basic compatibility Often based on a single resistance Often based on a single resistance
genegene Typically not durableTypically not durable
Gene for gene Gene for gene interactionsinteractions
HostHost RR rr PathogenPathogen AA resistresist suscsusc aa suscsusc suscsusc basic compatibility overcomes nonhost basic compatibility overcomes nonhost
defensedefense pressure on host to detect pathogen leads pressure on host to detect pathogen leads
to (temporary) resistanceto (temporary) resistance pressure on pathogen to overcome/evade pressure on pathogen to overcome/evade
resistanceresistance
Breeding for resistanceBreeding for resistance
Identify likely targets, disrupt, look for Identify likely targets, disrupt, look for attenuation of pathogenicityattenuation of pathogenicity
Cross commercial susceptible strains to Cross commercial susceptible strains to wild relatives, backcross to retain yield wild relatives, backcross to retain yield and desireable characters in resistant and desireable characters in resistant strainstrain 8-10 years; resistance may last 3-5 years8-10 years; resistance may last 3-5 years
Pyramid strategiesPyramid strategies Horizontal resistanceHorizontal resistance