Masters Theses

Date of Award

8-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Ernest C. Bernard

Committee Members

Carroll J. Southards, Charles D. Pless, Kimberly D. Gwinn

Abstract

Tall fescue is the most widely planted forage species in Tennessee, with approximately 1.4 million hectares. This grass is used as pasture and hay feed for beef cattle, and is used to a lesser extent for dairy cows, sheep, and horses. A high percentage of tall fescue is infected with the endophytic fungus Neotyphodium coenophialum, which grows entirely within the plant and relies on it for nutrition and dissemination. Tall fescue infected with this endophyte (E+) has increased insect and nematode resistance, compare with endophyte-free (E-) tall fescue. However, the endophyte produces toxins that have negative effects in many organisms, such as fescue toxicosis in cattle. The objectives of this study were to determine if E+ tall fescue affected reproduction of the nematode Pratylenchus scribneri, and to determine if the egg hatch of this nematode was affected by chitinase.

Twenty-four plants each of E+ and E- tall fescue were transplanted into Conetainers in the greenhouse. Five hundred to 1,000 P. scribneri were pipetted into a hole at the base of each tiller. Eight root systems of E- and eight of E+ fescue were harvested and stained at 20, 40, and 60 days to determine nematode and egg numbers. Stage-specific distributions were determined by dissecting roots and removing stained nematodes, then measuring and categorizing them as J2, J3, J4, or adult. In the chitinase study, P. scribneri eggs were exposed to several serially diluted chitinase solutions. Numbers of hatched nematodes in each solution were counted every 3 days for 15 days.

In the reproduction and development study, P. scribneri was almost eliminated in E+ tall fescue. In E+ tall fescue, few eggs were observed in the roots. Significantly fewer egg and juvenile numbers were found in E+ tall fescue at 40 and 60 days compared with E- plants. Generally, no significant differences were observed in adult nematode numbers at any date. Thus egg production, but not survival, appeared to be reduced by E+ tall fescue.

The number of nematodes that hatched from eggs in chitinase solution decreased as the concentration of chitinase increased. Increased levels of chitinase in E+ tall fescue roots may cause egg disintegration or prevent eggshell formation in P. scribneri females.

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