Microbiology 530 - Introductory Plant Pathology
Exam 1- 50 pts.
1. What is a common leaf symptom and sign for the following plant pathogens: (6 pts.)
Fungus
Bacterium
Virus
2. You receive a diseased plant specimen and begin isolation procedures. Within 48 hr, you observe septate mycelium in the culture plate. (4 pts.)
What is one fungal or fungallike group that you are certain the pathogen does not belong to:
What is one fungal group that it might belong to:
3. Briefly, describe the purpose of Koch’s postulates and 2 situations in which their application may result in some difficulty. (4 pts.)
4. You receive some plant pathogenic bacterial cultures in the mail, but the labels have fallen off. The labels say: Clavibacter, Erwinia,and Xanthomonas. What characteristics of these cultures will allow you to replace the labels properly? (6 pts.)
5. Plant pathogenic bacteria produce no spores. How do they survive Massachusetts winters? (2 pts.)
6. What are the biological characteristics that define the fungi?
Why are Plasmodiophoromycetes not true fungi?
Why are Oomycetes not true fungi? (6 pts.)
7. Immunoassays are rapid and accurate means to detect viruses. Why are bioassays still used (i.e. what are the advantages of bioassays)? (2 pts.)
8. Name 3 kinds of insects that commonly transmit plant viruses:
What are some limitations to the use of insecticides to prevent virus transmssion? (5 pts)
9. Ascomycetes and other fungal groups are classified by the sexual spores and fruiting bodies that they produce. How are Imperfect Fungi (Deuteromycetes) classified? Use examples in your answer. (3 pts.)
10. You receive a package that contains plants that may have been injured by herbicide drift or may have a virus. With no further information, how might you determine which is the problem? (2 pts.)
Fill in the correct word. 10 pts. Do all 12 for extra credit.
designation of bacterial subspecies based on host plant
structure on mycelium that is found only in Basidiomycetes
early bacteriologist for whom a facultative anaerobic genus is named (first and last name)
most common type of nucleic acid found in plant viruses
motile, asexual spore
open, cup-shaped ascocarp/ascoma
pear-shaped fruiting body with opening at the top, containing conidia
sexual spores of the Ascomycetes
general term for an organism with nuclei
a parasite that requires a living host
a mass of mycelium with a dark rind
virus transmission that can occur without a latent period
1. You receive two plants in your diagnostic lab. One is infected with lesion nematodes and the other by root-knot nematodes. (4 pts.)
a. What root symptoms does each type of nematode cause?
b. For which nematode problem would you suggest use of a genetically resistant cultivar and why?
2. What are 2 ways to determine if a plant is infected by a phytoplasma or a virus (4 pts.)
3. Name 2 plant pathogens (or their diseases) that produce growth regulators and the symptoms they cause. (4 pts.)
4. Name two other chemical weapons commonly produced by plant pathogens (2 pts.)
5. Give an example of an obligate parasite from each of the following plant pathogen groups:
fungi:
nematodes:
prokaryotes:
viruses
6. Are all plant pathogens equally affected by environmental factors? Explain your answer with a few brief examples (6 pts.).
7. Name a common insect vector for each of these parasites (3 pts.)
Phytoplasmas:
Viruses:
Xylem-limited fastidious bacteria
8. Water is an important factor for infection by many (but not all) pathogens. What are 3 ways to minimize the time that leaves remain wet? (3 pts.)
9. You are a plant pathogenic fungus, so think like a fungus! Use appropriate terminology.
a. Describe how you might survive the impending Massachusetts winter (list of possible ways is fine) (3 pts.)
b. If you are a foliar pathogen, how will you get from the soil to the leaves of a new host plant and re-establish an infection (2 pts.)
c. If you are a root pathogen, how will you find and infect the roots of your host plant (2 pts.)
d. As a human being (now think like a person!), what are 3 ways you can interfere with these processes? (3 pts.).
Fill in the correct term. 10 pts. Do all 12 for extra credit.
a) Endoparasitc, migratory nematode (genus or common name- extra credit for both)
b) Host-specific, endoparasitc, sedentary nematode (genus or common name, extra for both)
c) Dioecious plant parasite of conifers
d) The coordinated timing of production of parasite inoculum and host susceptibility
e) Plant tissue in which spiroplasmas are found
f) Thick-walled asexual survival spore
g) Another general term for an obligate parasite
h) Structure that helps keep a germinating spore from falling off a leaf
i) Nutrient-rich area produced by root exudates
j) An enzyme that is produced continuously by an organism (an adjective, not a specific type)
k) Plant growth regulator discovered from studies of the “foolish seedling” disease of rice
l) Adjective that describes bacteria that require complex media for growth
1. What are 2 sources of genetic variation that exist in both fungi and plants?
Do fungi or plants have the advantage in terms of genetic variation? Explain your answer. (4 pts.)
2. What are 2 ways to prolong the usefulness of a resistance gene in an annual crop? (2 pts.)
3. What are 3 limitations (biological or agricultural) to the use of crop rotation?
Explain why crop rotation works so well to reduce the populations of many soilborne pathogens. (5 pts.)
4. Briefly, explain how government regulations minimize pesticide residues at the time of harvest. (3 pts.)
5. What are 2 ways that heat can be used to reduce pathogen inoculum? (2 pts.)
6. What is an advantage and a disadvantage to the use of meristem culture for the production of propagative plant material (2 pts.)
7. Penetrant/systemic fungicides are more subject to resistance than contact/protectant fungicides. What are 2 advantages to penetrants that make them attractive for disease management? (2 pts.)
8. The following statements are false. Write a correct statement. (10 pts.)
When genetically-resistant plants develop disease, the resistance gene has “broken down” and no longer functions.
Because of the intense movement of plants and people around the world, quarantines are no longer needed.
If a compound has a high LD50, it is relatively nontoxic and people should not be concerned about their exposure to it.
All fungicides are equally likely to result in the development of resistant fungal strains with intensive use.
All pesticides are equally likely to be groundwater contaminants.
ESSAY QUESTIONS. Choose only 2. 10 pts. each.
The genetic interaction between hosts and parasites has been described as a “chess game.” Explain this analogy. Then, explain how cultural practices and environmental conditions can modify the outcome of such an interaction.
You have a plant with genetic resistance conferred by a single gene for tomato yucky spot, a new and devastating polycyclic fungal disease. You also have a contact/protectant fungicide that is effective against the fungus that causes yucky spot. Describe a management plan that will provide good stewardship of the resistance gene and the afailable fugnicides and also provide reliable tomato crops in the coming years.
Integrated pest management (IPM) is the mainstay of modern agriculture. Explain how an understanding of monocyclic and polycyclic pathogens and the relative effect of reducing initial inoculum and epidemic rate can be used to create effective integrated disease management programs. Use graphs to illustrate your answer.
Extra credit:
Who provided the experimental evidence that led to the gene-for-gene theory?
Name any of the 3 diseases that led to the first US quarantine legislation in 1912.
Part I. T or F. If false, explain why. Use an example. (20 pts.)
1) Indicator plants used to detect plant viruses are always inoculated by rubbing infective sap on the leaves.
2) All plant pathogens are parasites.
3) Wind is always an important factor in the dissemination of fungal spores.
4) Angular leaf spots are a common symptom of bacterial infection.
5) Sclerotia are produced only by Ascomycetes.
6) All plant pathogenic prokaryotes can be grown in culture.
7) Micronutrient deficiencies can often be corrected by adjusting soil pH.
8) All plant pathogens produce toxins and enzymes that degrade plant cells.
9) Stunting is a common symptom of nematode injury.
10) Powdery mildew fungi remain on the leaf surface, so they should not really be called parasites.
Part II. Match the correct genus name. 10 pts.
Venturia Pythium
Striga
Agrobacterium
Meloidogyne
Botrytis
Aspergillus
Verticillium
Pseudomonas
Alternaria
1) Root-knot nematode 2) Vascular wilt fungus
3) Includes soft-rot bacteria
4) Apple scab
5) Most common cause of damping-off
6) Conidia with alternating horizontal and vertical septa
7) Crown gall
8) Gray mold disease
9) Produces aflatoxin
Part III. Write the correct term 10 pts.
1) closed sexual fruiting body of powdery mildew fungi
2) the “exogenous dormancy” that keeps spores from germinating too soon
3) pleomorphic mollicute
4) full scientific name (genus and species) name for a xylem-limited fastidious bacterium
5) feeding structure of a nematode
6) Gram+ genus of plant pathogenic bacteria
7) The person who first proved that a fungus caused a plant disease following the Irish potato famine
8) Sexual spores of Oomycetes
9) Structure on mycelium that is found only in Basidiomycetes
10) Thick-walled asexual spore
Part IV. Short answers. 40 pts.
1) Name 6 survival spores or structures produced by plant pathogenic fungi (3 pts.).
2) Name one secondary air pollutant and its source (2 pts.)
3) What are 2 ways that bacterial diseases are different from most fungal diseases of plants? (2 pts.)
4) Choose a plant pathogenic Oomycete, Ascomycete, and Basidiomycete and fill in the chart:
Example Survival structure Mycelial characteristics
5) Why has fungicide resistance become a significant problem only since the late 1970s?
6) Name 3 alternatives to chemical control for nematodes. Discuss briefly, a limitation to the use of each. (6 pts.)
7) Briefly, describe how the knowledge of whether a pathogen is a monocyclic or a polycyclic pathogen can help in the design of an effective disease management program. (3 pts.)
8) You have been given a stunted plant. What are 3 possible pathogen causes of this symptom, and how can you determine which one is the causal agent? (6 pts.)
Pathogen Diagnosis
9) What are 2 symptoms that suggest an abiotic problem rather than a biotic one? (4 pts.)
10) What are 2 features of Oomycetes that exclude them from the true Fungi? (4 pts.)
11) Describe one successful example of a plant disease biological control and why it works. (2 pts.)
Part V. Final essay. Choose only one. 20 pts.
Many people in the general public would like to see “chemical” pesticides banned and replaced with biological controls. Discuss some of the advantages and disadvantages of both chemical and biological disease management. How do you think that plant disease management, in general, should be optimized in this new century?
OR
Describe the basic biology of the major groups of plant pathogens and what adaptations they have made to become parasites of plants. Consider, for example, survival, dispersal and infection.
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Updated: July 7, 2001