Name _____________________





1.  (16 pts)  Define the following:























            virulence factor




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 (___) Florida or in

 (___) New York?

(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.






4.  (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)









5. (6 pts)  Define host specific toxin.  Give an example of this type of toxin and explain how it works to cause disease.






6.  (12 pts) List 2 enzymes that pathogens use 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 factor.









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





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











10.  (12 pts)  A local nursery has called you to look at Persea indica saplings. These small evergreen trees, related to avocado and bay laurel trees, are popular for landscapes in warmer locations.  The manager tells you that they recently got a large shipment of the trees in with wilt, leaf necrosis, and brown discoloration of sapwood.  Your internet research tells you that it could be Laurel wilt caused by the fungus Raffaelea lauricola which is vectored by tiny wood boring beetles.  Alternatively, the symptoms could be due to localized nutrient and irrigation problems and minor insect feeding.  When you go look at the saplings 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 trees have the Laurel wilt disease. (Fungicide and insecticide are difficult to inject into the trees.)  Answer the question again (comparing the use of plant resistance and cultural control) for a field of corn with bacterial leaf spot.