ENDOPHYTE INFECTION EFFECTS ON STOMATAL CONDUCTANCE, OSMOTIC ADJUSTMENT AND DROUGHT RECOVERY OF TALL FESCUE

Presence of the endophytic fungus Acremonium coenophialum Morgan-Jones and Gams in tall fescue (Festuca arundinacea Schreb.) enhances host p ersistence in drought-prone environments. However, the physiological m echanism is not well understood. We investigated the influence of endo phyte infection and water deficit on osmotic adjustment, stomatal cond uctance, tiller survival and leaf elongation rate of genotype GA87-122 and cv. Kentucky-31 (KY31) of tall fescue. Plants were grown in a gre enhouse in pots containing fine-silty topsoil (experiment 1) or sand ( experiment 2). In expt 1, endophyte-infected (EI) and endophyte-free ( EF) isolines of GA87-122 were exposed to two drought preconditioning c ycles, after which all pots were re-watered and osmotic adjustment det ermined. Osmotic adjustment was -0.46 and -0.51 MPa in EI leaf blades and tiller bases and -0.29 and -0.13 MPa in EF leaf blades and tiller bases, respectively. In expt 2, EI and EF GA87-122 and KY31 were expos ed to severe drought after two preconditioning cycles, then re-watered . During the second preconditioning drying cycle of KY31, stomatal con ductance tended to be lower in EI than in EF plants, but the differenc e was significant (P less than or equal to 0.05) only at two sampling times. Shoot tissues osmotically adjusted 0.17-0.31 MPa more in EI tha n in EF plants. Tiller survival and leaf elongation rates were higher (P less than or equal to 0.05) in preconditioned EI than in EF plants. Basal-zone osmotic adjustment was correlated with tiller survival rat e in GA87-122 and KY31 (r = 0.87, P less than or equal to 0.01 for bot h). Enhanced osmotic adjustment in the meristematic and growing zone m ight account for improved survival of tillers by facilitating protecti on of the apical meristem.