Mode of action of tremorgens

Ryegrass staggers is a neurotoxic disorder of livestock grazing perennial ryegrass (Lolium perenne L.) infected with the endophytic fungus Neotyphodium lolii. Ryegrass staggers was first reported in 1880 (Anonymous 1880) although at this stage the cause of the observed tremorgenic disorder was unknown. The presence of an endophyte within perennial ryegrass was first recognised in 1935 (Neill 1941) but it was not until 1981 that the correlation between endophyte infection and the incidence of ryegrass staggers was established (Fletcher & Harvey 1981; Mortimer et al. 1982). The tremorgenic compound, lolitrem B, produced by the endophyte was then isolated and implicated in the disease (Gallagher et al. 1981, 1982, 1984). The future then seemed clear: eradicate the endophyte and solve the ryegrass staggers problem. Endophyte-free plots, however, showed little growth and suffered severe damage from the larvae of Argentine Stem Weevil (Mortimer et al. 1982). The correlation between endophyte levels, weevil numbers and tiller damage was then made (Prestidge et al. 1982) and a few years later the beneficial effects of endophyte were shown to be due to peramine, an antifeedant produced by the fungus (Gaynor & Rowan 1986; Rowan et al. 1986).