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24 Cards in this Set

  • Front
  • Back
Define virulence.
degree of severity of disease
Define monocyclic disease cycle.
has only the primary infection, i.e. Sclerotinia sclerotiorum
Define polycyclic disease cycle.
has a primary and secondary infection, increases spread, i.e. Phytophthora infestans
Define appressorium.
swollen, flattened portion of a fungal filament that adheres to the surface of a higher plant, providing anchorage for invasion by a fungus
Name some mechanical forces for infection for fungi, bacteria, viruses, and nematodes.
fungi--appressorium and penetration peg
bacteria and viruses-- vectors
nematodes-- stylets
Name some chemical weapons of pathogens.
enzymes (soft rots, wilts), toxins (Bipolaris), growth regulators (crown gall, clubroot), polysaccharides (bacteria)
What is tabtoxin?
a nonhost specific microbial toxin
What happened during the southern corn leaf blight epidemic?
There was a monoculture of hybrid plant with sterile male cytoplasm susceptible to the disease, which produced T toxin that inhibited ATP synthesis
What are examples of growth regulators?
auxins, gibberellins, cytokinins, ethylene
What is inoculum density?
a measure of the number of propagules of a pathogenic organism per unit area or volume
What is a propagule?
any part of an organism capable of independent growth
How can fungi, bacteria, and viruses survive?
Fungi--on or in soil, on plants, on or in seed, and on or in vegetative propagative organs through resting structures
Bacteria-- same as above but no resting structures
Viruses-- on or in insects
How do plant pathogens disseminate?
wind, rain, insects, irrigation or flooding, contaminated seeds, infected transplants, animals, boots, pruning shears
Compare primary inoculum and secondary inoculum.
primary inoculum-- inoculum, usually from an overwintering source, that initiates disease in the field, as opposed to inoculum that spreads disease during the season (secondary inoculum)
How does direct penetration take place using an appresorium?
melanin accumulates in the appressorial cell wall and turgor pressure builds up
What are the 3 forms of ingress?
direct penetration, wounds, natural openings
What important enzymes are there in pathogen attack?
pectinase (breaks down polysaccharides), cutinase (breaks down fatty acids)
What are constitutive and induced enzymes?
constitutive means its present in cells at all times and induced means its produced by cell in response to internal or external activators
How are cellulose, lignin, starch and lipids attack by pathogens?
through enzymes
C/C nonhost specific and host specific toxins.
Nonhost specific toxins produce all or part of the disease syndrome not only on host plant, but also on other pecies not normally attacked; increase the severity of disease by increasing the virulence of the pathogen.
Host specific toxins is a substance produced by a pathogen only toxic to the hosts of that pathogen and has no toxicity against nonsusceptible plants; most of these toxins must be present for the microorganism to be able to cause disease
What is auxins, what does it cause and what are 2 examples of disease?
growth regulators, causes hypertrophy and hyperplasia, examples: clubroot, root knot nematodes
What is tabtoxin?
a nonhost specific toxin that inactivates the enzyme glutamine synthetase; the molecule itself is not toxic
What is an example of a nonhost specific toxin and the pathogen that produces it?
oxalic acid-- Sclerotinia spp.
What is an example that uses the nonhost specific toxin, pyricularian?
Magnaporthe grisea (rice blast)