Name _____________________





1.  (16 pts)  Define the following:


primary inoculum






avirulence factor






            suppressive soils



            systemic acquired resistance






            verical 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.  In which state would the disease be more common if the crop were grown there (__) Nevada or (__) Maryland?

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




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








5. (4 pts)  Phytotoxicity is a potential problem when using chemical control of plant diseases.  Give 2 factors that influence whether a chemical will be phytotoxic..







6.  (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 use to cause disease and the symptoms associated with an excess of the plant growth factors.









7. 8 pts)  List four defense mechanisms, one of each type of  1) induced structural, 2) induced biochemical, 3) preformed structural, and 4) preformed 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 viruses.











10.  (12 pts)  The manager of a local nursery phones you to come look at his boxwood plants.  He says that the shrubs are stunted, and the leaves have chlorotic and necrotic spots. He is worried that he may have boxwood blight, caused by the fungus Cylindrocladium pseudonaviculatum.  He read that it is a large problem in Europe and parts of the US, including North Carolina, Ohio, and Oregon, that the disease is worse in warm humid environments, and that it survives in leaves, cankers, and plant debris. Confirmation of the disease in his plants will cause a huge problem, since there is a quarantine on shipping or selling plants with the disease and it would be the first report of that disease in the state.  He wonders if instead the boxwoods might have a nutrient deficiency combined with excessive heat. When you go look at the boxwoods 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 boxwood shrubs have the fungal disease.  Answer the question again (compare the use of plant resistance and cultural control) for a local wheat field infected with rust.