How Pathogens Attack Plants
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- 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.
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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 toxin that inactivates the enzyme glutamine synthetase; the molecule itself is not toxic
- 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?
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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.
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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 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)