I. In each of the questions below, there are two choices marked A) and B) with which to complete the statement. Either answer, both answers, or neither answer may be correct. You are to circle all the answers, if any, that correctly complete each statement; i.e., circle one, or both, or neither of the letters in each question (40 pts).
1. Multiple applications of a foliar fungicide serves to A) reduce r, B) delay the onset of disease.
2. Failure of inherently susceptible plants to become diseased, even though disease is prevalent, is A) escape, B) tolerance.
3. The cuticle is an example of a(n) A) constitutive, B) induced host defense mechanism which functions to hinder direct penetration by fungal pathogens.
4. Long distance transport of systemic fungicides within a plant occurs primarily in the A) phloem, B) xylem tissue.
5. Crop rotation will be successful as a disease management strategy if the pathogen has a A) narrow host range and survival structures, B) broad host range and no survival structures.
6. Shape of a disease progress curve for a monocyclic disease plotted over many seasons would be A) inverted J, B) sigmoid.
7. For solarization to be effective in reducing populations of soilborne plant pathogens, the soil must be A) wet and covered with black plastic, B) wet and covered with clear plastic.
8. The greatest multiplication of polycyclic pathogens occurs during the A) exponential phase, B) logistic phase.
9. The phase of the sigmoid disease progress curve where environment is limiting is A) exponential, B) terminal.
10. Source of secondary inoculum for repeating disease cycles is A) diseased tissue, B) crop refuse.
11. A kind of fungal sexual spore is a A) conidium, B) urediospore.
12. When the macroenvironment is suboptimum for disease development, sprinkler irrigation will facilitate disease under a A) dense canopy, B) sparse canopy.
13. A) Length of time of inoculum production, B) susceptibility of host tissue, determines the number of applications of a foliar fungicide for control of monocyclic diseases.
14. The result of increasing the number of plants per acre is to A) increase duration of leaf wetness, B) support a higher relative humidity within the canopy.
15. For a polycyclic disease such as potato late blight, planting of late blight-free seed tubers acts to A) delay the epidemic in time, B) reduce the rate of the epidemic.
16. Plant parasitic nematodes are identified to Order on A) structure of esophageal region, B) presence of stylet.
17. In the third year of a wheat monoculture, the severity of take all root rot can be reduced by the application of A) ammonium-based, B) potassium-based fertilizers at planting.
18. The rust pathogen, Puccinia striiformis, gains entry into the host through A) wounds, B) stomates.
19. A nematode that periodically tunnels inside a root and then moves back out into the soil is called a A) migratory endoparasite, B) sedentary ectoparasite.
20. The A) Ascomycetes, B) Basidiomycetes is (are) a group of numerous species of fungi whose sexual or perfect stage is known.
II. Agricultural practices can have a direct effect on disease epidemics. Below is a list of some of these practices. For each item on the list, indicate in the blank which of the important three epidemiological variables, initial inoculum (Xo), infection rate (r), or time (t) is primarily affected. (16 pts)
___________1. crop rotation
___________2. state border inspections
___________4. hot water seed treatment
___________5. plant architecture
___________6. late maturing cultivars
___________7. irrigation frequency
___________8. open field burning
III. Effectiveness of a protectant fungicide for controlling polycyclic foliar diseases is a function of the r-value. In general, the greater the r value, the lower the effectiveness of the fungicide. Please explain why this statement is true. (4 pts)
IV. Match the terms in the left-hand column with those in the right hand column by placing the correct letter of the most appropriate answer in the space provided. (18 pts)
_____1. additive gene action
_____2. environmentally regulated
_____3. reduces r
_____4. reduces xo/Q
_____5. race x cultivar interaction
_____6. ranking of isolates always constant
_____7. lengthens latent period
_____8. cultivar mixtures
_____9. spatial deployment
|A. Vertical Resistance
B. Horizontal Resistance
V. A wholesale nursery near Woodburn, Oregon sold Japanese maples to a retail nursery in both New York and California. In the table below are disease readings for Verticillium wilt and a bacterial leaf spot at both out-of-state nurseries one year later.
bacterial leaf spot
|New York nursery
1. What explanation might be given for the similar amount of Verticillium wilt at both nurseries? (2 pts)
2. Give two explanations for the large differences in amount of bacterial leaf spot between the two nurseries. (4 pts)
VI. To prevent or delay the onset of resistance to systemic (narrow spectrum) fungicides, it is recommended that antiresistance strategies be initiated early before resistance becomes a problem. Name two tactics a grower might use for minimizing the risk of developing fungicide resistance in the pathogen population and explain the underlying rationale for each approach. (4 pts)
VII. The following is a table of susceptible and resistant disease reactions on apple varieties that have been inoculated with different isolates of the apple scab pathogen.
||Apple scab isolates|
|Red Delicious R1
|Granny Smith R5__
1. There are ____________ races of the pathogen. (2 pts)
2. On the table above, give the disease reaction (R or S) of each isolate on Liberty. (3 pts)
3. A hypersensitive reaction is observed with isolates 1, 2, 3 and 4 on the Fuji with genotype R3__ . Describe a hypersensitive reaction. (2 pts)
4. Explain the biological basis by which Braeburn is resistant to isolates 1, 2, and 3 but susceptible to isolates 4, 5, and 6. (6 pts)
VIII. Typhula blight, caused by the sclerotial forming Basidiomycete, Typhula incarnata, is a disease problem of turf where snow cover occurs throughout much of the winter. Instead of using fungicides to manage this monocyclic disease, you as the golf course superintendent, have decided to manage the disease without pesticides. A newly formed organic farming company is marketing two biocontrol agents, SCLERBOMB, a fungus, and MORETURF, a bacterium.
1. SCLERBOMB is disked into the soil before the turf is laid. Explain how would this control Typhula blight? (2 pts)
2. What effect, if any, would this treatment have on the onset of Typhula blight? (2 pts) Explain your answer for a 3 pt BONUS.
3. MORETURF is applied to the turf as a foliar spray where it produces an antibiotic. Explain how would this control typhula blight? (2 pts)
4. What two cultural practices could the turf manager employ to enhance disease suppression by SCLERBOMB? (4 pts)
5. A single application of MORETURF was applied at two rates: 1 lb and 3 lbs/A. The 3 lb rate was 3 times more effective in suppressing disease than the 1 lb rate. Give one biological reason why the 3-lb rate performed better than the 1-lb rate of the biocontrol product. (3 pts)
IX. A friend of mine produces pathogen-tested chrysanthemum planting stock for sale to commercial greenhouses. Recently, she received cuttings of a new variety of chrysanthemums from a commercial greenhouse operation in Colorado. She plans to produce planting stock of this variety for sale on the West Coast. Because chrysanthemums are very susceptible to Erwinia chrysanthemi, a bacterium that causes vascular wilt, special care must be taken to prevent the perpetuation of this bacterium.
1. Why is meristem tip culture the preferred procedure to produce the mother plant? (3 pts)
2. Disease symptoms would not be seen in the mother plant even if the pathogen were present. Why? (3 pts)
3. The mother plant was indexed for the presence of this pathogen using the serological test of ELISA. The test came back negative, but upon culturing a portion of the stem on crystal violet pectate agar, a selective-differential medium for soft rot erwinias, the bacterium was isolated. Give two biological reasons for the false negative result. (4 pts)
X. You observe the following diseases in broccoli and on the basis of your field observations you made a preliminary diagnosis of their identity. Write the laboratory procedures you would use to verify your field diagnosis. (12 pts)
1. root rot nematode
2. Phytophthora root rot
3. turnip yellow mosaic virus
4. bacterial soft rot
XI. Three farmers grow snap beans, and all three fields are afflicted with Hypothetical Blight disease. The pathogen overwinters on host debris and is favored by high humidity levels. The curves below represent disease progress models for the three fields.
1. Compared to Farmer A, which farmer cleaned up last year's bean debris? (2 pts)
2. Of the three factors that determine disease severity in the disease progress model, which one was affected by this practice? (2 pts)
3. Compared to Farmer A, which farmer manipulated her planting pattern to lower relative humidity? (2 pts)
4. Of the three factors which determine disease severity, which of the three factors did this affect? (2 pts)
5. If you were Farmer B and wanted to claim that you have less disease than Farmer A, would you use area under the disease progress curve, final proportion of disease, or apparent infection rate? (2 pts)
6. If you were Farmer C and wanted to claim that you had less disease than Farmer A, which measure would you use? (2 pts)
7. If you could somehow make the latent period of this polycyclic pathogen longer than a single growing season, what shape would you expect your disease progress curve to have? Draw it on the same graph (2 pts)