Name _____________________





1.  (16 pts)  Define the following:





            suppressive soils



            systemic acquired resistance






            vertical resistance



primary inoculum






avirulence factor



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 specifics for each side of the triangle.  In which state would the disease be more common if the crop were grown there (__) Arizona or (__) Wisconsin?

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




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








5. (4 pts)  Resistance is a potential problem when using chemical control of plant diseases.  Explain what fungicide resistance is and give 3 ways that it can be controlled.







6.  (12 pts)  List 4 enzymes that pathogens used to cause disease and the modes of action of the enzymes and indicate whether they are used early, middle, or late in the infection process.









7. 8 pts)  List 4 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 causes symptoms.






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











10.  (12 pts)  A small organic farmer phones you to come look at her quinoa plantings near Cloudcroft.  This grain is native to the high plains of Peru and Bolivia and is highly nutritious. The grower is trying to be the first to introduce the crop into New Mexico, since it could be very profitable. She says that the plants germinated and emerged poorly, leaving a poor stand and many of the plants look stunted and a few have necrotic spots on the leaves. She is worried that they may have Fusarium leaf spot and Rhizoctonia (a soil borne fungus) damping off (death of seeds and seedlings). She read that they are common problems in Peru and that both pathogens could be found in New Mexico soils. Alternatively, she wonders if instead the quinoa may be germinating poorly and growing poorly due to excessive heat. Quinoa is known to require cool temperatures and grow very poorly when temperatures exceed 95F. When you go look at the planting 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 quinoa have one or both of the fungal diseases.  Answer the question again (compare the use of plant resistance and cultural control) for a local wheat field infected with rust.