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25 Cards in this Set
- Front
- Back
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What is nonhost resistance?
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when a plant is in contact with a pathogen to which is is not a host; lacks recognition factors; most common form of resistance in nature
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What is host resistance?
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ability of the host to hinder the growth and/or the deveopment of the pathogen
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What is vertical resistance?
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host possesses specific genes (R) that are active against specific pathogenic races only, and are controlled by single genes or major genes. Hypersensitive response.
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What is horizontal resistance?
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(Partial Resistance or Rate-reducing Resistance) Host, using polygenic control, has a reduced susceptibility to all races of the pathogen
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What are the components of host plant resistance?
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incubation period
latent period lesion length lesion expansion number of sporulation lesion/mm2 number of spores/mm2 |
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What is incubation period?
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the time between penetration of a host by a pathogen and the first appearance of disease symptoms
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What is latent period?
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the time between infection and the production of new inoculum; the time after a vector has acquired a pathogen and before it can be transmitted
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What are some constitutive structural plant defenses?
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waxes, epidermal cell walls, stomato, thick walled tissues
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What are some induced structural plant defenses?
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cytoplasmic (becomes granular), cell wall defense structures (form lignintuber, papilla), histological
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What are the histological defense structures?
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Abscission layers (middle lamella dissolves cutting infection off)
Cork layers (blocks spread and stops flow of nutrients and water to infection) Tyloses (overgrowth of protoplast into xylem) |
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What are some preexisting chemical plant defenses?
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tanins, preformed plant proteins, hydrolytic enzymes
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How did plant pathologists and corn breeders solve the Southern corn leaf blight epidemic?
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Produced a cultivar that didn't have the specific receptor protein molecule (URF13) to react with the T toxin
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What are some induced biochemical plant defenses?
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Hypersensitive response
Active oxygen species Reinforcement of host cell walls with strengthening molecules Pathogensis-related proteins Phenolic compounds Phyolexins SAR |
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What are the steps in a hypersensitive response?
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1) Nucleus moves toward the invading pathogen and soon disintegrates
2) Brown, resin-like granules form in the cytoplasm, first around the point of penetration of the pathogen and then throughout the cytoplasm 3) Invading hyphae begins to degenerate and cannot spread any further 4) Complete destruction of all cellular components followed desiccation and necrosis of leaf tissue |
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How does silicon affect Magnaporthe grisea (rice blast)?
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decreased severity of disease
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What is the difference between Systemic Acquired Resistance (SAR)and Induced Systemic Resistance?
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SAR- is triggered by a pathogen triggering the HR and the production of certain chemicals
ISR- induced by nonpathogens such as rhizobacteria, induces structural defenses and phytolexin but not antimocrobial PR proteins |
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What are the 4 types of resistance?
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nonhost, vertical, horizontal, apparent
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What is the 4 outcomes of gene-for-gene reaction?
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Avr/R gene + recognition = HR (rapid cell death)
Avr/R gene, no recognition = disease No Avr/R gene, recognition = disease No Avr/R gene, no recognition = disease |
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What is apparent resistance?
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plants remain free from infection or symptoms and thus appear resistant; can be caused by disease escape or tolerance
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What is the role of pathogenicity genes in development of plant disease (virulence factors)?
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recognition of host by pathogen, attachment of pathogen to host, germination and formation of infection structures, plant cell wall-degrating enzymes, toxin, phytolexins
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What are the general mechanisms of variability in plant pathogens?
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Mutation
Recombination Pathogen fitness |
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What are fungi's specialized mechanism of variablity?
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Heterokaryosis
Heteroploidy Parasexualism |
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What are bacteria's specialized mechanism of variablity?
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conjugation
transformation transduction |
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What are virus's specialized mechanism of variablity?
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genetic recombination
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What is vegetative incompatibility and why is it important?
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Vegetative hyphae of same fungal species come in contact will not fuse.
Important b/c it is a defense mechanism against harmful nuclei, mitochondria, plasmid and viruses |
