LONG-TERM CHANGES OF ENDOPHYTE INFECTION IN TALL FESCUE STANDS

Pastures of tall fescue (Festuca arundinacea) presumed to be free of the endophytic fungus (Acremonium coenophialum) had increasing levels of endophyte, averaging 4% per annum over periods of 9-12 years. Similarly, replicated plots sown at four levels of initial endophyte infection increased in infection over a 4-year period: for example, plots with a 27% initial level increased to 84%, and those with a level of 58% increased to 92% by the fourth year. Mowing plots to prevent seed formation did not affect the rate of change in infection percentage, except that plots with 0% initial endophyte began to show detectable levels in unmown blocks, presumably, as a result of contamination by seed from adjacent infected plots. By the fourth year of the study, fescue plant densities, measured by plant counts, as well as ground cover, were significantly higher in plots with high initial endophyte level. It is proposed that the change in infection percentage was due to enhanced survival of infected plants in mixed stands where there was intense competition for available moisture in conditions of drought.