Nematode resistance in tall fescue

Tall fescue, Festuca arundinacea. an important forage grass in the southeastern United States, is frequently infected with Acremonium coenophialum. an endophytic fungus associated with fescue toxicosis in livestock. Endophyte-free (E-) tall fescue is more difficult to establish and are not as resistant to environmental stress and pests as endophyte-infected (E+) tall fescue. Greenhouse trials were conducted on three species of plant-parasitic nematodes with different feeding patterns to compare populations on E+ and E- tall fescue. Presence or absence of the endophyte was determined with PAS-ELISA. After 15 weeks, numbers of Pratylenchus scribneri. a migratory endoparasite, were significantly higher on E- than on E+ tall fescue roots. After 8 weeks, numbers of egg masses and eggs of Meloidogyne graminis, a sedentary endoparasite, were significantly higher on E- than on E+ tall fescue. Numbers of Helicotylenchus pseudorobustus, an ectoparasite, were not significantly different on E- and E+ tall fescue after 8 weeks. Numbers of an undescribed species of Meloidogyne, which is parasitic on legumes, were unaffected by presence of E+ or E- tall fescue in the rhizosphere. Results of these experiments suggest that substances within E+ tall fescue roots may be inhibitory or toxic to some plant parasitic nematodes. These substances have not been identified. A bioassay using P. scribneri as the test organism was developed to determine toxicity of alkaloids and other compounds isolated from E+ tall fescue. Nematodes were exposed to test compounds for 48 hours; survivors were allowed to exit the test system for 72 hours and were counted. Ergotamine tartrate was more toxic to nematodes than saturated pyrrolizidines.