Name _____________________





1.  (12 pts)  Define the following:





primary inoculum






virulence factor



hypersensitive response



            systemic acquired resistance




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?  Would the disease be more common if the crop were grown in Wisconsin or Alabama?

(For 4 extra credit points, answer the question for another of the diseases listed.)












3. (4 pts)  Define nonhost resistance.  How effective is 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 nonhost specific toxin.  Give an example of this type of toxin and explain how it works to cause disease.






5.  (12 pts)  List 4 enzymes that pathogens used to cause disease and the modes of action of the enzymes and indicate for each whether they are used early, middle, or late in the infection process.









6. (8 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 onion breeder for a new seed company has asked you to come look at his breeding plots because his onion seed stalks have large dead areas on them and are falling down.  He has heard about a new thrips-transmitted virus disease of onions, iris yellow spot virus. Confirmation of the disease in his rare breeding stock will cause a huge problem, since he wonÕt be able to use the plants.  Alternatively, the onions may a Botrytis (a common fungus) infection. When you go to the field 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 Botrytis or iris yellow spot virus. Compare the use of plant resistance and cultural control for a local wheat field infected with rust.









11.  (6 pts)  What is horizontal resistance?  List an advantage and a problem with growing plants with only this type of resistance.