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Botany 350 - Midterm 1 (1999)


I. Correction True or False. If the statement is true write TRUE in the blank. If the statement is false, correct the underlined words so the statement reads true by writing the correct word(s) in the blank provided (38 pts).

_____________________ 1. The perithecium is the pear-shaped sexual fruiting body of the Ascomycetes.

_____________________ 2. Viruses move from plant cell to plant cell through sieve elements.

_____________________ 3. Long distant movement of viruses in the plant occurs in the xylem tissue.

_____________________ 4. Plant parasitic nematodes are nonsegmented round worms.

_____________________ 5. The life strategy of plant parasitic nematodes that cause the most damage on a worldwide basis is the migratory ectoparasite.

_____________________ 6. Bacterial pathogens can survive as epiphytes, in lenticels or in the vascular tissue of plants.

_____________________ 7. All plant viruses have a core of nucleic acid enclosed by a lipid envelope.

_____________________ 8. The cell walls of the Oomycetes are composed of chitin.

_____________________ 9. Coenocytic mycelium is characteristic of the fungal class Ascomycetes.

_____________________ 10. Bacteria are eukaryotic organisms.

_____________________ 11. Plant parasitic nematodes are distinguished from saprophytic nematodes by the presence of a spicule.

_____________________ 12. Distribution of diseased plants is often patchy when the disease originates from soilborne inoculum.

_____________________ 13. Zoospores are fungal spores that are formed as a result of meiosis.

_____________________ 14. With vascular wilts, uptake of water and minerals is impaired.

_____________________ 15. Nematode sensory structures are located on the cuticle.

_____________________ 16. A facultative aerobe can reproduce in the absence of oxygen.

17. Alter the underlined words in the following sentence if they are incorrect so that it is a true serological statement.

A rabbit was injected with a purified antibody (............................) for a specific viral plant pathogen and a specific polyclonal (........................) antiserum was recovered that was used to recognize this pathogen by its unique fluorescence (.....................) in an ELISA test.


II. Chose the one best definition and place the letter of that definition in the space provided next to the disease symptom (7 pts).

_______ 1. blight 

_______ 2. wilting 

_______ 3. canker 

_______ 4. scab 

_______ 5. soft rot 

_______ 6. spot 

_______ 7. gall 

A. well-defined area of necrotic tissue

B. hyperplasia

C. necrosis of entire leaves, shoots, branches

D. loss of cell turgor

E. sunken, necrotic lesions on woody and fleshy stems

F. overgrowth of epidermal cells

G. maceration of tissue

III. This fall I received some carrot plants that had symptoms of sunken leaf spots and defoliation; some of the plants were also stunted. The leaf spots were distributed randomly on the leaves. The grower indicated that plant symptoms occurred as foci throughout the field. The literature suggests a fungus causes the disease.

1. What was (were) the primary symptom(s)? (2 pts)





2. Define primary symptom. (2 pts)





3. What was (were) the secondary symptom(s)? (2 pts)





4. Define secondary symptom. (2 pts)





5. Explain why a secondary symptom by itself should not be used for diagnosis of a disease (2 pts)





6. A routine examination of the diseased tissue was done. If a fungus were the cause, what specific structures might the diagnostician observe microscopically? (2 pts)





7. A selective medium was used to isolate the fungus into pure culture from the diseased tissue. Define selective medium. (2 pts)





8. How does a selective medium differ from a differential medium? (2 pts)





9. Is the organism a necrotroph or a biotroph. Justify your answer. (3 pts)






1. The life cycle of a plant virus is initiated upon entry of a plant cell. What are two ways this can happen? (2 pts)





2. Once the virion enters the cell it uncoats to expose the genome. What are the three genes found in every plant virus genome? (3 pts)





3. After the virus uncoats how are the three genes translated into proteins? (2 pts)





4. What process produces additional viral genomes? (2 pts)





5. List the three additional steps that must occur for disease to develop within a plant. (3 pts)





V. Serology has proven to be a powerful tool for the identification of plant pathogens. Initially, polyclonal antisera were used for identification purposes, but in the 1970's the highly specific antisera, called monoclonal, was developed. Each, however, has its advantages and disadvantages in disease diagnosis.

1. What is the major difference between polyclonal and monoclonal antisera? (2 pts)







2. The procedure for producing polyclonal antiserum differs from that for monclonal antiserum. Describe how the procedures differ. (3 pts)







3. False positives and false negatives are possibilities with either kind of antisera. Describe one biologically based scenario under which a false positive could occur and one scenario for a false negative. (6 pts)






VI. In the box below indicate with an X if the diagnostic tools in the left column that are ROUTINELY used to identify the pathogen groups listed across the top (10 pts)

viruses bacteria  fungi  nematodes

Differential medium


Gram stain

Fruiting body



Electron microscope


VII. The Tylenchida and Dorylaimida are two orders of nematodes containing plant parasites. What are the morphological structures that differentiate these orders? (3 pts)