Name _____________________





1.  (14 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 (___) New Mexico 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.


3.  (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 an incompatible 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 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, two structural and two biochemical, that plants can use to prevent pathogen infection and explain how each works.









7. (6 pts)  Resistance is a potential problem when using chemical control of plant disease.  Explain what fungicide resistance is and give three ways that it can be controlled





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











9.  (12 pts)  A local pecan grower has recently expand into growing walnuts.  He has asked you to come look at the young walnut plantings because he has noticed yellowing and dieback, and insect holes in the bark.  He is concerned that he might have thousand cankers disease, caused by the fungus Geosmithia morbida, and moved around by bark beetles.  This disease was first identified in northern New Mexico around 10 years ago.  The grower is worried that his new plantings could be a total loss within 3-5 years.  Alternatively, the symptoms could be due to localized irrigation problems and minor insect feeding.  When you go look at the walnuts 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 walnuts have thousand cankers disease. (Fungicide or insecticide have not been very effective.)  Answer the question again (comparing the use of plant resistance and cultural control) for a field of corn with bacterial leaf spot.