Plant Defense

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What is nonhost resistance?: 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
What is host resistance?: ability of the host to hinder the growth and/or the deveopment of the pathogen
What is vertical resistance?: host possesses specific genes (R) that are active against specific pathogenic races only, and are controlled by single genes or major genes. Hypersensitive response.
What is horizontal resistance?: (Partial Resistance or Rate-reducing Resistance) Host, using polygenic control, has a reduced susceptibility to all races of the pathogen
What are the components of host plant resistance?: incubation period
latent period
lesion length
lesion expansion
number of sporulation lesion/mm2
number of spores/mm2
What is incubation period?: the time between penetration of a host by a pathogen and the first appearance of disease symptoms
What is latent period?: 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
What are some constitutive structural plant defenses?: waxes, epidermal cell walls, stomato, thick walled tissues
What are some induced structural plant defenses?: cytoplasmic (becomes granular), cell wall defense structures (form lignintuber, papilla), histological
What are the histological defense structures?: 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)
What are some preexisting chemical plant defenses?: tanins, preformed plant proteins, hydrolytic enzymes
How did plant pathologists and corn breeders solve the Southern corn leaf blight epidemic?: Produced a cultivar that didn't have the specific receptor protein molecule (URF13) to react with the T toxin
What are some induced biochemical plant defenses?: Hypersensitive response
Active oxygen species
Reinforcement of host cell walls with strengthening molecules
Pathogensis-related proteins
Phenolic compounds
Phyolexins
SAR
What are the steps in a hypersensitive response?: 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
How does silicon affect Magnaporthe grisea (rice blast)?: decreased severity of disease
What is the difference between Systemic Acquired Resistance (SAR)and Induced Systemic Resistance?: 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
What are the 4 types of resistance?: nonhost, vertical, horizontal, apparent
What is the 4 outcomes of gene-for-gene reaction?: 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
What is apparent resistance?: plants remain free from infection or symptoms and thus appear resistant; can be caused by disease escape or tolerance
What is the role of pathogenicity genes in development of plant disease (virulence factors)?: recognition of host by pathogen, attachment of pathogen to host, germination and formation of infection structures, plant cell wall-degrating enzymes, toxin, phytolexins
What are the general mechanisms of variability in plant pathogens?: Mutation
Recombination
Pathogen fitness
What are fungi's specialized mechanism of variablity?: Heterokaryosis
Heteroploidy
Parasexualism
What are bacteria's specialized mechanism of variablity?: conjugation
transformation
transduction
What are virus's specialized mechanism of variablity?: genetic recombination
What is vegetative incompatibility and why is it important?: 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

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