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Botany 350 - Final (1999)


I. Match the elements in the first column with the form of resistance in the second column. There is only one correct answer per element (20 pts).

1. _______ Rate limiting 

2. _______ Delay in onset of epidemic 

3. _______ Pathogen races

4. _______ Quantitatively inherited

5. _______ Nonspecific resistance

6. _______Gene for gene hypothesis

7. _______Major gene resistance

8. _______ Cultivar mixtures

9. _______ Incompatible host-parasite interaction

10. ______ Stable over time


A. Vertical Resistance

B. Horizontal Resistance


II. 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 the statement reads true by writing the correct word(s) in the space provided (38 pts).

1._____________________ Crop rotation is a successful disease control tactic if the pathogen has a narrow host range.

2._____________________ Peppermint fields in the Willamette Valley are burned in the fall for control of rust.

3._____________________ Burning of grass seed fields in the Willamette Valley is primarily for control of root diseases.

4._____________________ Nonfumigant nematicides are not seriously phytotoxic and can be applied as post-plant treatments for perennial crops infected with nematodes.

5._____________________ For soil fumigation to be effective, the optimum soil temperature is 60-68 F.

6._____________________ To suppress root diseases that are favored by high pH (basic soil) ammonium fertilizers are recommended.

7._____________________ Long distance transport of systemic fungicides within a plant occurs primarily in the xylem tissue.

8._____________________ Plant parasitic nematodes are necrotrophs.

9._____________________ A pycnidium is an asexual spore bearing structure of both the Ascomycetes and Dueteromycetes.

10._____________________ Fungistasis in the inhibition of fungal spore germination in the absence of a susceptible host.

11._____________________ If two fungicides have the same mode of action, cross-resistance is seen a pathogen population.

12._____________________ The effect of several applications of a protectant fungicide is to delay the onset of an epidemic by a polycyclic pathogen.

13._____________________ The limiting factor for infection of foliage by most fungal and bacterial pathogens is nutrients.

14._____________________ With five differential hosts, it is possible to identify 16 races.

15._____________________ A thin, black polyethylene tarp is used for solarization because it transmits most of the solar radiation that heats the soil.

16._____________________ The shape of the disease progress curve for diseases caused by monocyclic pathogens is sigmoid.

17._____________________ Antigens are new or altered proteins produced in a warm-blooded animal as a reaction to a foreign protein.

18._____________________ By growing plants on raised beds for disease suppression, the target is the environment.

19._____________________ When the macroenvironment is suboptimal for development of wet weather diseases, sprinkler irrigation will have no effect on disease if the canopy is sparse.


III. Septoria leaf blotch is a perennial foliar disease problem of wheat in the Willamette Valley of Oregon. Instead of using fungicides to manage this disease, you have decided use alternative disease management strategies. A newly formed organic farming company is marketing two biocontrol agents, PYCNOBOMB and HEMANWHEAT, that are bacteria.

1. PYCNOBOMB is applied to the stubble after harvest. How would this help to control the leaf spot (2 pts)?





2. What effect would this treatment (PYCNOBOMB) have on onset of leaf blotch symptoms the next growing season (2 pts)?





3. HEMANWHEAT is applied to the crop at the flag leaf stage, where it produces an antibiotic. How would this control the disease (3 pts)?





IV. You observe the following diseases in the field and on the basis of your field observations you made a preliminary diagnosis of their identity. How would you verify (confirm) your field diagnosis in the laboratory (12 pts).

1. red leaf maple with Verticillium wilt









2. potato tubers with Columbia Basin root knot nematode









3. Manhattan rye grass (lawn) with stripe rust









4. Yellow zucchini squash with curly top virus.







V. Place the letter of each CULTURAL practice after the most appropriate category (9 pts).

Practices that evade or exclude the pathogen _______________________________________

Practices the reduce the amount of initial inoculum _______________________________________

Practices that decrease the effectiveness of initial inoculum ________________________________

Practices that suppress the rate of epidemic development _______________________________________


A. Eradication of alternate hosts

B. APHIS inspection of baggage

C. Soil pH adjustment

D. Refrigeration of harvested produce

E. Form of nitrogen

F. Crop rotation

G. Seeding date

H. Certified planting stock

I. Irrigation timing



VI. Below is a table with the disease reactions on a set of 4 differential hosts of barley inoculated with 9 different isolates of stripe rust. S = susceptible; R = resistance.

Stripe Rust isolates

1 2 3 4 5 6 7 8 9
Differential host (genotype)                  
R1R1 R R S R R R S S S
R3R3 S S S S R R S R S
R4R4 R R R R R R S S R
R5R5 S R S R S R S R R

1. How many races of stripe rust are there ____________ (2 pts)?

2. From the information given in the above table, indicate on the table below the type of reaction (R or S) these same isolates would produce on a host with the following genotype R3R3R4R4 (3 pts).

Stripe Rust isolates

1 2 3 4 5 6 7 8 9

Differential host


3. Which isolate is the most virulent on this set of differentials and why (3 pts)?






4. Isolate 1 induces a hypersensitive reaction on plants with genotypes R1R1 and R4R4. Describe hypersensitive reaction (3 pts).





5. Now explain the mechanism why disease did not occur on the differential host with the R1R1 genotype by isolate 1 (4 pts).





6. Now explain the mechanism why disease did occur on the differential host with the R3R3 genotype by isolate 1 (4 pts).





7. The kind of resistance illustrated above is Vertical Resistance. This form of resistance is not stable over time. Explain why it is not stable (4 pts).








8. The genotypes listed in the first table represent different barley cultivars that are grown in Klamath Falls.

a. Describe two strategies for managing the Vertical resistance genes that would prolong the usefulness of these cultivars (4 pts).


b. Indicate the effect of each strategy on both the initial inoculum and the apparent infection rate (2 pts).



VII. The following simplified diagrams are for two kind of climates called Continental and Mediterranean types.

1. Using the information from the diagrams above, indicate which climate is most favorable for bacterial diseases of the foliage and explain why (4 pts).







2. For disease to develop on foliage by a bacterium, growth (multiplication) on the surface of leaf is an essential component. Describe two disease management practices that could suppress this growth (4 pts).









3. Bonus (2 pts): Which climate is found in the Willamette Valley of Oregon?




VIII. Resistance to fungicides with site specific modes of action in a pathogen population occurs more frequently with polycyclic pathogens than with monocyclic pathogens.

1. Why is this true (3 pts)?





2. Discuss two fungicide use strategies that would delay the buildup of resistant strains and the rationale for these strategies (6 pts).






IX. Below are disease progress curves for early blight of tomato at three locations (A, B, and C) in the southern United States. The broad spectrum, protectant fungicide, chlorothalinol, was applied at each site. Obviously, disease control varied across sites. There are several explanations (fungicide resistance is NOT one) for the less than stellar control at some of the sites with this fungicide. Give three plausible explanations for the variation in efficacy of this fungicide and explain your answers (9 pts).








X. Chrysanthemums are grown in nurseries at several locations across the United States. Two diseases of concern are white rust, which was recently introduced into the United States, and a vascular wilt caused by the soft rot bacterium, Erwinia chrysanthemi. The planting stock was generated in a nursery in northern Oregon and shipped to a nursery in New York and a nursery in California where the number of cuttings was increased 1000-fold. In the table below are assessments on amount of both diseases in these two nurseries.

% rust % wilt
Disease Location    
New York 2 76
California 35 8


1. Give two explanations of why rust was more severe at the California nursery compared to the New York nursery and explain the reasons for your choice (6 pts).





2. Give one explanation why the vascular wilt was more severe at the New York nursery compared to the California nursery and explain why this would result in more disease (3 pts).