ENDOPHYTE EFFECTS ON GROWTH AND PERSISTENCE OF TALL FESCUE ALONG A WATER-SUPPLY GRADIENT

Ecophysiology of the endophyte (Acremonium coenophialum Morgan-Jones and Gams)-tall fescue (Festuca arundinacea Schreb.) association needs to be understood in order to promote environmental fitness traits of the association while reducing its deleterious effects on ruminants. Our objective was to determine the influence of endophyte on drought stress tolerance, persistence, and yield components of field-grown tall fescue on a Typic Hapludalfs soil. A water supply gradient was established during 1989 and 1989 with line-source irrigation on established populations of 0 and 80% endophyte-infected tall fescue. Whole plots consisted of endophyte infection status, across which a gradient of water was applied in a strip-split fashion with eight replicates. Tiller population density and herbage yield were determined every 28 d and yield components were measured on selected dates. Relative to populations receiving high irrigation (375-650 mm applied), tiller density in nonirrigated stands (0-50 mm applied) from July to October 1988 was reduced an average of 42% in infected tall fescue and 55% in noninfected tall fescue. Tiller density of nonirrigated, infected populations recovered fully to that of high irrigation treatments by 17 November, whereas that of nonirrigated, endophyte-free populations recovered to only 62% of irrigated treatments. The advantage in population density due to endophyte infection continued throughout 1989, a relatively wet year. A benefit in total forage yield due to endophyte infection was not consistently evident because of greater yield per tiller in endophyte-free stands in 1989. Enhanced tiller density and survival were associated with endophyte infection during severe water deficit, and this advantage continued throughout the subsequent year. Endophyte infection confers population stability in tall fescue during drought stress through improved tiller and whole plant survival.