Link to home

Botany 350 - Final (1998)

I. Bacterial spot of zucchini can be a serious problem in the humid southeastern United States. From the information given in the article (click here for the article), answer the questions posed on the next two pages.

1. What is the name of the pathogen? (2 pts)

2. What is the name of the disease? (2 pts)

3. What is (are) the sources of primary inoculum? (2 pts)

4. How is the pathogen disseminated within the crop? (2 pts)

5. How does the pathogen gain entry into the foliage and into the fruit? (2 pts)

6. Is this a polycyclic or monocyclic disease? (1 pt)

7. Assume that the latent period for this disease was either 6 or 21 days. How effective would destruction of crop refuse at the end of the season be as a tactic for managing this disease the next season for a 6-day latent period versus a 21-day latent period? Explain your answer (4 pts).









8. Some disease suppression could be achieved if seed free of the bacterial pathogen was available. Outline the steps you would follow to produce a large enough quantity of pathogen-free true seed of zucchini for sale to commercial zucchini growers (8 pts).















9. As one disease control tactic, the recommendation is to manage the irrigation water. If trickle irrigation is NOT an option and water could be applied only by sprinklers,

a. develop an sprinkler irrigation program to manage this disease (4 pts)






b. explain the rationale for your strategy (3 pts).







II. A particular pathogen has a latent period of 2 years. Circle the disease progress model that best describes disease development over one season. (2 pts)

1. Is disease development based on the amount of initial inoculum or current disease level? (1 pt)




2. Three parameters describe this curve, and each can be altered to provide disease control. Name the three parameters (don't give the mathematical symbol) and give an example of a disease management tactic that affects each parameter. (6 pts)







III. Consider the following situation: A crop is favored by warm temperatures and is attacked by two pathogens. Pathogen A is a fungus that survives as sclerotia in soil and infects roots best at a soil pH of 6.0. Pathogen B is a fungus that survives in debris of the previous crop. The spores are splashed onto leaves and cause blight symptoms under cool temperatures and long periods of leaf wetness. Discuss for pathogen A and for pathogen B the probable effects on disease development for the following management practices (12 pts).

1. Crop rotation

Pathogen A:

Pathogen B:



2. Ammonium fertilizer

Pathogen A:

Pathogen B:



3. Soil fumigation

Pathogen A:

Pathogen B:





IV. List four reasons or conditions that reduce the effectiveness of soil fumigation (4 pts).







V. 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 (26 pts)

1. With (A) polycyclic pathogens (B) monocyclic pathogens, the effect of reducing xo is to delay the epidemic.

2. The human eye recognizes healthy tissue most readily at (A) low, (B) high levels of disease.

3. Pathogens that kill host cells in advance of invasion to obtain nutrients are (A) biotrophs, (B) necrotrophs.

4. Shifts in virulence patterns of plant pathogens may occur as a result of (A) sexual recombination, (B) mutation.

5. The effect of horizontal resistance is to (A) delay the onset of the epidemic, (B) reduce the rate of disease increase.

6. Horizontal resistance reduces amount of disease caused by polycyclic pathogens by (A) shortening the length of the latent period, (B) increasing lesion size.

7. Vertical resistance genes when combined in a cultivar mixture act to (A) reduce the amount of initial inoculum, (B) reduce the apparent infection rate.

8. Nematodes that vector plant viruses are (A) sedentary endoparasites, (B) migratory ectoparasites.

9. Number of applications of a protectant fungicide is a function of (A) susceptibility of host tissue, (B) duration of inoculum production.

10. By growing plants on raised beds for disease suppression, the target is the (A) pathogen, (B) environment.

11. When the macroenvironment is optimal for disease development, sprinkler irrigation will have no effect on disease if the canopy is (A) sparse, (B) dense.

12. Plant pathogenic nematodes are identified to class based on (A) structure of esophageal region, (B) presence of stylet.

13. The proposed mechanism of action of bicontrol of take all root rot of cereals includes (A) antibiosis, (B) parasitism.


VI. List and describe three mechanisms of action for biological control of plant pathogens (6 pts)









VII. The following is a table of resistant and susceptible disease reactions on a set of differential apple hosts for apple scab, caused by Venturia inaequalis. Each cultivar was inoculated with a different isolate of the pathogen.


V. inaequalis isolates

Differential hosts







Fuji (R1R1)







Granny Smith (R3R3)







Red Delicious (R5R5)








1. There are ____________ races of Venturia inaequalis. (3 pts)

2. From the information given in the above table, indicate on the table below 1) the genotype of each pathogen isolate and 2) the type of reaction (R or S) these same isolates would produce on Braeburn that has the genotype of R1R1R5R5. (6 pts)

V. inaequalis isolates

Differential hosts 1 2 3 4 5 6

Pathogen Genotype







Braeburn (R1R1R5R5)








3. A hypersensitive reaction was observed with isolate 2 on Fuji. Define hypersensitive reaction. (3 pts)



4. Explain why Granny Smith is resistant to isolates 1, 3 and 5 and susceptible to the other three isolates. (5 pts)



5. Resistance to apple scab is not stable. Explain what happens when resistance to a disease 'breaks down'. (4 pts)




VIII. My cousin Shirley is the production coordinator for a company that produces poinsettias. Two major disease problems that are prevalent prior to the Christmas season are bacterial soft rot caused by Erwinia carotovora and gray mold, caused by Botrytis cinerea. Bacterial soft rot develops on stem cuttings and gray mold occurs on the developing bracts.

1. Describe in detail the laboratory procedures and/or tests you would use to determine that Erwinia was the cause of bacterial soft rot. (4 pts)


2. Describe in detail the laboratory procedure and/or tests you would conduct to determine that Botrytis was the cause of gray mold. (3 pts)


This company has greenhouses located in Santa Monica, CA and Tallahassee, FL. The source of the propagation stock for both greenhouses is Woodburn, OR. In the table below are the disease readings taken on the Saturday following Thanksgiving Day.

Disease Incidence

Bacterial soft rot Botrytis blight
Santa Monica 5 % 75 %
Tallahassee 90 %

20 %

3. Provide two explanations why bacterial soft rot was more severe in Florida than in California. Be specific in your answer. (4 pts).


4. Provide two explanations why gray mold was more severe in California than in Florida. Be specific with your answer. (4 pts).




IX. Below are disease progress curves for Fusarium patch, caused by the fungus Microdochium nivale (formerly Fusarium nivale) of annual blue grass at five golf courses in the Pacific Northwest this past summer. Although the systemic fungicide, Bayleton, was applied at these sites, control was not equal across locations.

a. Give two reasons for lack of fungicide efficacy at some of the sites (6 pts).







X. Management strategies to extend the usefulness of both vertical resistance genes and narrow spectrum fungicides (at-risk fungicides) have some similarities. What are these strategies and the underlying bioloigcal reasons for them. (6 pts)










XI. In the plant pathology world, there are numerous terms that start with the letter P. Select five terms starting with this letter and give a definition of each (15 pts)