EPWS 310 PLANT PATHOLOGY EXAM 1, Fall 2009
1. (12 pts) Define the following:
2. (8 pts) Using one of the 3 historical diseases discussed in class ( coffee rust, late blight, or southern corn leaf blight) discuss the disease in relation to the disease triangle. What were the important factors contributing to the epidemic? Give the specifics of each side of the triangle.
Would the disease be more common if the crop were grown in (___) Georgia or in
(For 4 extra credit points, answer the entire question for another of the diseases listed.)
3. (6 pts) Define horizontal resistance. List an advantage and a problem with growing plants with only this type of resistance.
3. (10 pts) Does an incompatible interaction end in disease? What combination of resistance and virulence can the host and pathogen have that will result in an incompatible interaction? Which combinations give a compatible interaction. (Hint: Consider the gene for gene theory)
4. (6 pts) Define host specific toxin. Give an example of this type of toxin and explain how it works to cause disease.
5. (12 pts) List 2 enzymes that pathogens used to cause disease and the modes of action of the enzymes and 2 plant growth factors that pathogens used to cause disease and symptoms associated with an excess of the plant growth factors.
6. (12 pts) List four defense mechanisms, one of each type of induced structural, induced biochemical, preformed structural and preformed biochemical that plants can use to prevent pathogen infection and explain how each works.
7. (4 pts) Phytotoxicity is a potential problem when using chemical control of plant disease. Give two factors that influence whether a chemical will be phytotoxic.
8. (8 pts) Diagram a disease cycle and explain which steps in the cycle would differ between fungi and viruses.
9. (12 pts) The NMSU golf course manager has asked you to come look at the golf course because he has noticed circular dead areas on them. He is concerned that he might have spring dead spot, caused by Ophiosphaerella. This disease is common on Bermuda grass in Texas and Oklahoma, but has not been reported in New Mexico. Confirmation of the disease the on the golf course will cause a huge problem, since fungicides donŐt adequately control the fungus and there is little plant resistance. Alternatively, the turf may be infected with Fusarium or Pythium, which are more common fungi. When you go to the golf course for the first time what will you look for in diagnosing the problem? Since you need to be completely sure of your diagnosis, what steps will you need to go through to prove what is causing the problem?
10. (10 pts) Compare the use of plant resistance and cultural control for the next season if the onions have Fusarium or spring dead spot. Answer the question again (comparing the use of plant resistance and cultural control) for a different field of corn with bacterial leaf spot.