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Botany 350 - Final (1997)

I. Match elements in the first column with the associated structure or structures in the second column. Elements may have more than one answer and the structures may be used more than once (14 pts).

II. Make your own disease! Draw and label the disease cycle of a hypothetical bacterial disease of blueberries. Indicate whether it is monocyclic or polycyclic; how it overwinters; and what the primary and secondary inocula (if any) are. Your disease cycle need not be complex, but should be internally consistent and consistent with your general knowledge of bacteria (7 pts). Naming the disease is worth 1 bonus point.

III. For many years development of a biocontrol agent for control of white rot of onion, has been a concerted effort of many pathologists who work with this disease. The sclerotial-forming fungus, Sclerotium cepivorum, causes this disease. This past year, there was a report of a bacterium providing control of this disease. The reported mechanism of action was parasitism. Describe how you might demonstrate a cause and effect relationship between this bacterium on its host, the sclerotia of S. cepivorum (7 pts).

IV. This summer you observed the following diseases in a mint field. On the basis of your field observations you made a preliminary diagnosis of their identity. Describe the procedures/tests you would use in the laboratory or greenhouse to verify your field diagnosis (9 points).

1. mint with root lesion nematode

 

 

2. mint with Verticillium wilt

 

 

3. mint with curly top virus

 

 

 

V. Two greenhouse rhododendron growers purchased rootstock of the same variety of rhododendron from the same producer at the same time and planted them in their respective glasshouses. One year later when you visited each greenhouse you observed the incidence of gray mold and Phytophthora root rot. 

	Grey Mold	Root rot
Grower A	10 %	25 %
Grower B	90 %	0 %

Give two reasons for the difference in amount of gray mold and two reasons for the differences in amount of Phytophthora root rot between the two growers (12 pts).

1. Grower A

 

 

2. Grower B

 

 

 

VI. 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. In the blank provided write the letters of the answers that correctly complete each statement; i.e. one, both, or neither of the answers may be correct (34 pts).

___________ 1. Multiple applications of a foliar fungicide serves to (A) reduce r, (B) delay the onset of disease.

___________ 2. To suppress diseases that are favored by high soil pH, (A) nitrate, (B) ammonium fertilizers are recommended.

___________ 3. The effect of increasing the plant density is (A) increased periods of leaf wetness, (B) higher relative humidity within the canopy.

___________ 4. An aggregated distribution of diseased plants within a field can be caused by (A) monocyclic seedborne pathogens, (B) polycyclic soilborne pathogens.

___________ 5. A plant virus is composed of (A) RNA + protein coat, (B) DNA + protein coat.

___________ 6. Pathogens that gain entry into a host by direct penetration include (A) bacteria and fungi, (B) bacteria and viruses.

___________ 7. When the macroenvironment is suboptimal for disease development, sprinkler irrigation will have no effect on disease when irrigation occurs in the (A) evening, (B) morning.

___________ 8. When the macroenvironment is submarginal for disease development, sprinkler irrigation will facilitate disease under a (A) dense canopy, (B) sparse canopy.

___________ 9. (A) Length of time of secondary inoculum production, (B) susceptibility of host tissue, determines the number of applications of a foliar fungicide for control of a polycyclic disease.

___________ 10. 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.

___________ 11. Plant parasitic nematodes are identified to order on (A) structure of esophageal region, (B) structure of stylet.

___________ 12. Systemic fungicides are translocated acropetally (upward) in the (A) xylem, (B) phloem.

___________ 13. Aphid transmission specificity of plant viruses is associated with (A) protein coat, (B) nucleic acid.

___________ 14. Crop rotation is of limited value for root pathogens with (A) broad host range, (B) long term survival structures.

___________ 15. Proposed biological control mechanism by which take all root rot of wheat is suppressed is (A) antibiosis, (B) parasitism.

___________ 16. Abiotic factors that reduce the effectiveness of soil fumigants are (A) soil temperatures above 85 F, (B) a saturated soil profile.

___________ 17. Vertical resistance is more valuable against (A) polycyclic diseases, (B) monocyclic diseases.

VII. List four characteristics that distinguish broad spectrum from narrow spectrum fungicides (8 pts).

VIII. On the following table are disease reactions (S or R) on a set of rice differentials inoculated with different isolates of the blast fungus.

1. How many races are there (2 pts)

 

2. Is this Vertical or Horizontal Resistance (2 pts)

 

3. From the information given in the above table

a. On the table below directly under the pathogen isolate number, write the genotype of each pathogen isolate (4 pts).

b. On the table below, across from the host genotype R1R1R3R3, write the reaction (R or S) these isolates would produce on this host (4 pts).

Pathogen isolates	1	2	3	4	5	6	7	8
Pathogen genotype
Host genotype R1R1R3R3

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

5. Explain the mechanism why disease did occur on the differential host with the R2R2 genotype by isolate 1 (4 pts).

IX. 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 three epidemiological variables, initial inoculum (Xo), infection rate (r), or time (t) is primarily affected (18 pts).

_____________1. crop rotation

_____________2. solarization

_____________3. plant architecture

_____________4. soil fumigation

_____________5. horizontal resistance

_____________6. field burning

_____________7. multilines

_____________8. planting date

_____________9. vertical resistance

X. In California, strawberry diseases such as bacterial bight and diseases caused by viruses have been nearly eliminated as problems by planting certified plants on treated soils. Pathogen-free plants are obtained as a result of indexing, heat therapy and meristem culture.

1. Describe/define meristem culture, indexing, and heat therapy (6 pts).

 

 

 

2. What is the purpose of each one of these steps (3 pts)

 

 

 

 

XI. Transgenic plants are an alternative to traditional breeding programs.

1. What are 3 benefits of transforming plants with foreign genes (6 pts)?

 

 

 

2. List two beneficial traits that can be inserted (4 pts).

 

 

 

3. What role does Agrobacterium tumefaciens play in the transformation of a plant (2 pts)