ACREMONIUM ENDOPHYTE EFFECTS ON TALL FESCUE DROUGHT TOLERANCE

Tall fescue (Festuca arundinacea Schreb.) is grown as a forage, turfgrass, and conservation grass from the Gulf Coast to Canada in the eastern USA. The presence of endophytes in grasses can confer resistance to insect pests, enhance growth, and improve tall fescue persistence under high temperature and drought stress. Most tall fescue is infected with Acremonium cenophialum Morgan-Jones & Gams, a fungal endophyte. Our objectives were to determine the effects of endophyte infection on water relations and survival of water stressed (i.e., drought-stressed) tall fescue under greenhouse conditions. Endophyte-free and infected plants of three tall fescue selections were vegetatively propagated and grown together in 38-L weighing lysimeters to allow interplant competition for available soil moisture. Irrigation water and fertilizer were applied for 12 wk after planting before irrigation water was withheld for 8 wk. Water-relation characteristics including full-turgor osmotic potential (psi(pi100)), water potential at zero turgor (psi(L0)), relative water content at zero turgor (RWC0), apoplastic water fraction (beta), bulk modulus of tissue elasticity (epsilon), and the turgid weight to dry weight ratio (TW/DW) were determined before and after water stress. Osmotic adjustment (DELTApsi(pi)) was also determined. Endophyte infection did not affect psi(pi100), psi(L0), RWC0, and beta either before or after water stress and did not affect DELTApsi(pi). Endophyte infection did affect epsilon and the TW/DW ratio, but this effect was not sufficient to alter psi(L0). Total tillers, tiller survival, plant survival, and recovery weights were similar for endophyte-free and - infected plants. No evidence for endophyte-mediated drought tolerance was observed in this study. Based on this work, endophyte-mediated drought resistance may be due to alterations in drought avoidance.