A. First report of Sclerotium rolfsii on Jerusalem cherry (Solanum pseudocapsicum) in Europe.

Jerusalem cherry has recently become popular as a potted ornamental plant in Italy. During the summer of 1999, a sudden wilt of 60-day-old plants was observed in Northern Italy, an area of intensive floriculture. Initial symptoms included stem necrosis at the soil line and yellow and tan discoloration of leaves. As stem necrosis progressed, infected plants wilted and died. Necrotic tissues were covered with whitish mycelium that differentiated into reddish brown, spherical sclerotia. Sclerotium rolfsii was consistently isolated from the surface of symptomatic stem sections that were first disinfected for 1 min in 1% Clorox and then plated on potato-dextrose agar (PDA) amended with 100 ppm streptomycin sulfate.

1. What is the primary symptom? (2 pts)

2. What is (are) the secondary symptoms? (4 pts)

3. What is the difference between a primary symptom and a secondary symptom?

e.g. define the terms. (4 pts)

4. What is (are) the signs associated with the disease? (2 pts)

5. What is the difference between a sign and a symptom? (4 pts)

6. Was the medium used to isolate the pathogen a general medium or a selective medium? Explain your answer. (3 pts)

7. What is the cause of this disease? (2 pts)

8. This pathogen is a necrotroph. Define necrotroph. (2 pts)

9. This pathogen is a facultative saprophyte. What is the difference between a facultative saprophyte and a facultative parasite? (4 pts)

10. Outline the steps that you would follow to demonstrate that this fungus causes this disease (cause and effect relationship). (6 pts)

11. There is some indication that this pathogen produces a host specific toxin. What are two differences between host specific and non host specifc toxins? (i.e. define these two terms) (4 pts)

12. How could you determine if this toxin is, in fact, host specific? (2 pts)

13. No name was given to this disease. Be venturesome; give it an appropriate name. (2 pts)

14. This pathogen does not produce asexual or sexual spores and has no repeating cycle of disease during the season. In the space below diagram and label the disease cycle using the following terms: Inoculation, survival/overwintering, primary symptom, secondary symptom, colonization, penetration, sclerotium, canker, leaf chlorosis, hyphae. (5 pts)

B. The distribution of diseased plants in a field is information that diagnosticians use when determining what the disease is.

1. Name and diagram three ways that diseased plants are distributed in a field. (6 pts)

2. For each distribution pattern, discuss source of inoculum and whether secondary cycles of disease are involved during the current season (6 pts).

C. Some pathogens can not be seen with the aid of a dissecting or compound microscope and are not culturable on an artificial medium, e.g. viruses. Instead serological tests are routinely used in their identification. To do this, requires that antibodies be produced in a warm-blooded animal. Two kinds of antisera are commonly produced: monoclonal and polyclonal.

1. What is the primary difference between these two kinds of antisera? (2 pts)

2. What is an advantage of each? (4 pts)

D. The disease triangle is often used to illustrate the three main components which contribute to disease development.

1. What are these three components? (3 pts)

2. The disease pyramid includes a fourth component. What is this? (2 pts)

3. Disease symptoms lead to disruptions in the physiological processes of plants. For each of the symptoms listed below, fill in the primary physiological function of the plant which is affected. (5 pts)

Leaf spot ________________________

Root rot _________________________

Vascular wilt ______________________

Blossom blight _____________________

Tuber rot ________________________

E. True/False (20 pts)

1. ____________Oomycetes have septate hyphae.

2. ____________Tyloses are an example of a constitutive structural defense mechanism utilized by plants.

3. ____________Some Ascomycetes produce cleistothecia which serve as overwintering structures.

4. ____________Obligate parasites kill their hosts' tissue in order to obtain nutrients.

5. ____________The hypsensitive response is an example of an induced systemic defense response.

6. ____________Conidia are the asexual spores of the Ascomycetes.

7. ____________The Ascomycetes are also known as the "water molds."

8. ____________Hyperplasia is often a result of plant hormones produced by the pathogen.

9. ____________The most common method of inoculum dispersal is by humans.

10. ___________A resistant host is one that recognizes the pathogen and successfully defends itself.

F. The most common method for entry of plants by fungal pathogens is direct penetration through the leaf cuticle and cell walls.

1. What are 3 other routes or plant locations which fungal pathogens can take to penetrate plants? (3 pts)

2. What are 3 types of compounds which fungal pathogens use to cause disease? (3 pts)

Updated: January 3, 2001 (9:45am)