Name _____________________





1.  (14 pts)  Define the following:





primary inoculum






avirulence factor



hypersensitive response



               systemic acquired resistance






2. (6 pts)  Define tolerance as a type of host plant resistance.  List an advantage and a problem with growing plants with only this type of resistance.






3.  (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 specificis of each side of the triangle.  Would the disease be more common if the crop were grown in (__) Louisiana or (__) Pennsylvania?

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






4.  (10 pts)  Does a compatible interaction end in disease?  What combinations of resistance and virulence can the host and pathogen have that will result in a compatible interaction?  Which combinations give a compatible interaction? (Hint: Consider the gene for gene theory)








5. (6 pts)  Resistance is a potential problem when using chemicals to control plant disease.  Explain fungicide resistance and give two ways that it can be avoided.







6.  (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.









7. (8 pts)  List four defense mechanisms, 2 structural and 2 biochemical that plants can use to prevent pathogen infection and explain how each works.








8. (6 pts)  Define nonhost specific toxin.  Give an example of this type of toxin and explain how it works to cause disease.






9.  (8 pts) Diagram a disease cycle and explain which steps in the cycle would differ between fungi and bacteria.











10.  (12 pts)  The manager of a large tomato greenhouse operation in northern New Mexico phones you to come look at his plants.  He says that the plants are very stunted, and the leaves on the top part of the plant are yellow with purple veins and have necrotic margins on the leaves.  He says that the plants have only small poor quality fruit.  He is worried that he may have a new psyllid-transmitted bacterial disease caused by Candidatus-Liberobacter solanacearum in his tomatoes. Confirmation of the disease in his plants will cause a huge problem, since he wouldnÕt get any fruit from the plants and it would be the first report of that disease in the state.  He wonders if instead the tomatoes might have a nutrient deficiency. When you go look at the tomatoes 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?












11.  (10 pts)  Compare the use of plant resistance and cultural control for the next season if the tomatoes have the bacterial disease.  Answer the question again (compare the use of plant resistance and cultural control) for a local wheat field infected with rust.