How Pathogens Attack Plants

Front 1

Define virulence.

Back 1

degree of severity of disease

Front 2

Define monocyclic disease cycle.

Back 2

has only the primary infection, i.e. Sclerotinia sclerotiorum

Front 3

Define polycyclic disease cycle.

Back 3

has a primary and secondary infection, increases spread, i.e. Phytophthora infestans

Front 4

Define appressorium.

Back 4

swollen, flattened portion of a fungal filament that adheres to the surface of a higher plant, providing anchorage for invasion by a fungus

Front 5

Name some mechanical forces for infection for fungi, bacteria, viruses, and nematodes.

Back 5

fungi--appressorium and penetration peg
bacteria and viruses-- vectors
nematodes-- stylets

Front 6

Name some chemical weapons of pathogens.

Back 6

enzymes (soft rots, wilts), toxins (Bipolaris), growth regulators (crown gall, clubroot), polysaccharides (bacteria)

Front 7

What is tabtoxin?

Back 7

a nonhost specific microbial toxin

Front 8

What happened during the southern corn leaf blight epidemic?

Back 8

There was a monoculture of hybrid plant with sterile male cytoplasm susceptible to the disease, which produced T toxin that inhibited ATP synthesis

Front 9

What are examples of growth regulators?

Back 9

auxins, gibberellins, cytokinins, ethylene

Front 10

What is inoculum density?

Back 10

a measure of the number of propagules of a pathogenic organism per unit area or volume

Front 11

What is a propagule?

Back 11

any part of an organism capable of independent growth

Front 12

How can fungi, bacteria, and viruses survive?

Back 12

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

Front 13

How do plant pathogens disseminate?

Back 13

wind, rain, insects, irrigation or flooding, contaminated seeds, infected transplants, animals, boots, pruning shears

Front 14

Compare primary inoculum and secondary inoculum.

Back 14

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)

Front 15

How does direct penetration take place using an appresorium?

Back 15

melanin accumulates in the appressorial cell wall and turgor pressure builds up

Front 16

What are the 3 forms of ingress?

Back 16

direct penetration, wounds, natural openings

Front 17

What important enzymes are there in pathogen attack?

Back 17

pectinase (breaks down polysaccharides), cutinase (breaks down fatty acids)

Front 18

What are constitutive and induced enzymes?

Back 18

constitutive means its present in cells at all times and induced means its produced by cell in response to internal or external activators

Front 19

How are cellulose, lignin, starch and lipids attack by pathogens?

Back 19

through enzymes

Front 20

C/C nonhost specific and host specific toxins.

Back 20

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

Front 21

What is auxins, what does it cause and what are 2 examples of disease?

Back 21

growth regulators, causes hypertrophy and hyperplasia, examples: clubroot, root knot nematodes

Front 22

What is tabtoxin?

Back 22

a nonhost specific toxin that inactivates the enzyme glutamine synthetase; the molecule itself is not toxic

Front 23

What is an example of a nonhost specific toxin and the pathogen that produces it?

Back 23

oxalic acid-- Sclerotinia spp.

Front 24

What is an example that uses the nonhost specific toxin, pyricularian?

Back 24

Magnaporthe grisea (rice blast)