I. Correction True or False. If the statement is true, write TRUE in the blank. If the statement is false, CORRECT the underlined word(s) so that the statement reads true by writing the correct word(s) in the blank provided (22 pts).
1. ________________________________ For long distance dispersal of inoculum to occur, inoculum must be displaced into the laminar boundary layer.
2. ________________________________ The teliospore of the smut fungi is the overwintering structure.
3. ________________________________ The infective unit of plant parasite nematodes is the juvenile.
4. ________________________________ The period between inoculation and sporulation is termed the infectious period.
5. ________________________________ The human eye recognizes healthy tissue most readily at high disease levels.
6. ________________________________ The Basidiomycetes is an artificial group of numerous species of fungi whose sexual or perfect stage is unknown.
7. ________________________________ The proportion of stems with cankers to the total number of stems is a measure of disease severity.
8. ________________________________ A pycnidium is an asexual spore bearing structure of both the Ascomycetes and Deuteromycetes (Fungi Imperfecti).
9. ________________________________ The limiting factor for germination of most spores on foliage is nutrients.
10. ________________________________ Mushrooms, the fruiting body of some wood rotting fungi, have conidia located on their gills.
11. ________________________________ Sources of secondary inoculum for repeating cycles of disease are diseased plants.
II. Give two characteristics that differentiate circulative (persistent) from stylet-borne (nonpersistent) viruses (4 pts).
III. Draw a generalized disease cycle using all of the following terms. Some of the terms may be used twice (7 pts).
1. colonization, dissemination, host response, overwintering of survival structures, penetration, primary inoculum, secondary inoculum
2. Now add each of the following terms to your drawing under the step in the disease cycle to which it applies. Use each term only ONCE.
ascospores, conidia, haustoria, sclerotia, leaf spots (5 pts).
3. Now draw the disease progress model which would best describe this disease. Label the disease progress curve and graph axes. Indicate on the graph how each stage relates to the three components of the disease triangle (7 pts)
4. Why do disease progress curves flatten out late in the epidemic (2 pts)
5. What class of fungi would be characteristic of this pathogen (2 pts)
IV. Bacteria, fungi, nematodes and viruses have developed mechanisms to survive in the absence of its host or during periods of unfavorable environmental conditions. In the table below, match the pathogen group with the survival mechanism by placing an X in the appropriate box (11 pts).
V. A farmer growing beans in the Willamette Valley found that having 100 resting spores of the fungal pathogen Fusarium led to a severe (90%) root rot problem at 100 days. Using the appropriate equation given below:
Monocyclic disease progress model: ln 1/1-X = QRT
Polycyclic disease progress model: ln X2/1-X2 = ln X1/1-X1 + rt
1. Calculate the simple interest infection rate (4 pts). Show your work
2. If we assume the infection rate does not change, to what level would the farmer have to reduce the initial inoculum in order to have only 10% disease after 100 days (4 pts). Show your work.
3. If the disease were a foliar bacterial blight would reducing initial inoculum likely have LESS, the SAME or MORE effect on final disease than it does in the root rot case ( 2 pts)?
4. WHY? (2 pts)
VI. Confirmation of a diagnosis of a disease caused by a virus is frequently done with a serological test using either monoclonal or polyclonal antibodies.
1. Give two similarities and two differences in how monoclonal antiserum and polyclonal antiserum are produced. (4 pts)
2. What is the primary difference between polyclonal antibodies and monoclonal antibodies (3 pts)
3. In conducting any serological test, caution needs to be taken in interpreting results.
a. What is a false positive (2 pts).
b. Give two biological reasons for a false negative (4 pts).
c. Of the two, false negative and false positive, which is of greater concern and WHY (3 pts).
VII. Resistance to diseases such as stripe rust, powdery mildews, some smuts, late blight, and apple scab is frequently conditioned by a single dominant gene which has proven to be an unstable form of resistance over time.
1. A hypersensitive reaction is characteristic of this type of resistance (Vertical Resistance). Describe a hypersensitive reaction (2 pts).
2. Why does this resistance break down over time (2 pts)?
3. Races of the pathogen are associated with this kind of resistance. What is a race (2 pts)?
VIII. All plants have preformed and induced defenses that provide resistance against most pathogens.
What do the terms preformed and induced mean (4 pts).
2. Give an example of a preformed defense mechanism (2 pts).