The mechanism by which the endophyte confers resistance to nematodes in tall fescue is not known. The endophyte is not present in the roots; therefore, the fungus either induces physiological changes in the plant or produces toxins and repellents that are translocated to the roots. Indeed, resistance to insects in E+ tall fescue is due in part to alkaloids produced by the endophyte in the leaf sheath and translocation to the foliage (see Chapter 9). These alkaloids (see Chapter 13) deter insect feeding and reduce survival of insects that feed on the foliage of E+ plants (Siegel et al., 1990). Because ergot alkaloids are not involved in resistance to P. scribneri in perennial ryegrass (Lolium perenne L.) (Panaccione et al., 2006), they probably also are not involved in resistance to nematodes in tall fescue.