Masters Theses

Date of Award

8-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Ernest C. Bernard

Committee Members

Kimberly Gwinn, Bonnie Ownley, Charles Pless

Abstract

The population dynamics of Pratylenchus scribneri and P. agilis in endophyte-infected (E+) and endophyte-free (E-) tall fescue were examined with particular attention given to possible reproduction suppression or enzymatic degradation of eggshells. E+ and E- clonal pair tillers of tall fescue were planted in Conetainers and inoculated with 1,000 vermiform P. scribneri or P. agilis per Conetainer. P. scribneri trials were incubated at ambient temperature (ca. 25°C) and included a 14-week short-term study and a 30- week extended study. Short-term P. agilis trials were incubated at 30°C or 16.5°C to examine effects of temperature on endophyte-mediated resistance. Roots were harvested at 20, 40, and 60 days after inoculation, and the number of eggs and vermiform nematodes in each root system was counted. The first 50 vermiform nematodes or as many as possible up to 50, were dissected from each root system, mounted, and traced. The life-stage of traced nematodes was determined based on length and presence of a vulva. At all harvest dates during the short-term study, the mean number of vermiform P. scribneri in E+ roots was significantly lower than in E- roots. A persistent difference could not be established between P. scribneri populations in E+ and E- tall fescue during the extended study. Life-stage distributions during both the short-term and extended studies seemed to indicate a decrease in juvenile development in E+ tall fescue. Adult P. scribneri females were extracted from two E+/E- root systems for three consecutive harvests, surface-sterilized, and added singly to alfalfa callus cultures to determine reproductive capability. Females from both E+ and E- root systems reproduced in callus culture. P. scribneri eggs were exposed to bacterial chitinase solutions and examined with TEM to determine if increased levels of chitinase in E+ tall fescue roots might damage the integrity of eggshells. No difference was found between enzyme-treated eggs and control eggs. There was no significant difference between P. agilis populations in E+ and E- tall fescue incubated at 16.5°C. Life-stage distributions were similar and indicated reduced reproduction and development, probably due to the low temperature. Only three tall fescue tillers retained the endophyte after 60 days at 30°C. P. agilis populations were lower in the three E+ tillers; however, statistical analyses were not conducted due to the small sample size.

P. scribneri and P. agilis populations were negatively impacted by the presence of the endophytic fungus in tall fescue. The reproductive capability of female P. scribneri in E+ tall fescue was not permanently disrupted, nor was eggshell integrity compromised by exposure to bacterial chitinase. Slowed juvenile development may be partially responsible for the reduction in Pratylenchus populations in E+ tall fescue. Endophyte-mediated resistance is likely a complex of several mechanisms.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS