Date of Graduation

1999

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Committee Chair

William L. MacDonald

Committee Member

S. Clark Haynes

Committee Member

James Kotcon

Committee Member

Martin MacKenzie

Committee Member

Daniel G. Panaccione

Abstract

A series of biological tests were conducted to ascertain whether differences among isolates of the dogwood anthracnose fungus (Discula destructiva ) could be measured. Discula destructiva isolates were recovered from forty symptomatic eastern flowering dogwood trees growing at four locations in West Virginia and Pennsylvania. Before sampling, each tree was rated for percent foliage infected. Symptomatic leaf and twigs were collected in the summer of 1994 and D. destructiva was isolated from each leaf and twig sample. Isolates were cultured on potato dextrose agar (PDA) medium. Subcultures onto the same medium were made in order to evaluate growth and colony morphology. Two identical cultural tests were conducted and the diameters (mm) of all cultures were measured after three weeks of growth under 16/8 hr light at 24 C. No statistically significant differences in colony diameters were found among the isolates, although a small percentage of slow growing isolates were identified from each of the four sites. Only two slow growing isolates retained this feature in the second trial. Cultures typically produced slightly fluffy mycelium with concentric zonation patterns. Most of the isolates initially were pigmented light green but darkened with age. The few slower growing isolates were hard and rubbery to the touch and did not display concentric zonation. Another test was designed to establish whether a system of vegetative compatibility exists in D. destructiva. The isolates were paired on half strength PDA, water agar and each type of medium amended with dogwood leaves. Half of the plates were placed in the dark and half in 16/8 hour light. After 10 days of growth, the paired isolates were scored for the presence or absence of a barrage. The presence of a barrage was used as evidence of incompatibility between pairs. Barrage formation did not occur between any of the pairs, thus all paired isolates were considered to be vegetatively compatible. A double-stranded RNA (dsRNA) extraction procedure was the third assay attempted and was used to determine whether dsRNA was present in the isolates tested. All isolates contained dsRNA, as did their single conidial progeny. Many bands, however, were difficult to detect visually. The ability of isolates to invade plant tissue was measured in a fourth comparison by inoculating three different plant substrates, including apples, dogwood leaves and dormant dogwood stems. Lesion formation was observed in apples, but D. destructiva was rarely reioslated. A few lesions formed on the dogwood foliage but D. destructiva was never isolated. Lesions did not develop on inoculated dogwood stems. In all the apple, leaf and stem assays, a variety of other organisms were routinely isolated. Over all, when the inoculation procedures were employed, D. destructiva proved to be an unsuccessful pathogen. In all tests, D.

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