GROWTH AND WATER RELATIONS OF FIELD-GROWN TALL FESCUE AS INFLUENCED BY DROUGHT AND ENDOPHYTE

Field plots were established in autumn 1992 in which endophyte [Neotyp hodium coenophialum Glenn, Bacon, Price and Hanlin (formerly Acremoniu m coenophialum)]-infected (EC) and endophyte-free (E(-)) isolines of t hree tall fescue (Festuca arundinacea Schreb.) genotypes were planted. Plants were subjected to three water-withholding periods in 1993 and one in 1994, or were kept well watered throughout the experiment. Ther e were no consistent endophyte effects for leaf elongation, tiller den sity or dry weight per tiller. There were genotype X endophyte interac tions (P<0.01) for tiller density and shoot dry weight per area and ge notype X water X endophyte interactions (P<0.05) for cumulative leaf e longation in 1993. These interactions indicated the highly specific ef fect of host genotype-endophyte association on the expression of plant growth. Leaf rolling in the stressed treatments was more severe in E( -) than in E(+) plants in 1993, but there were no differences in 1994, and stomatal conductance tended to be lower in E(-) than in Ef plants in 1993. Fractional water content of the lower 3 cm of the youngest f ully developed leaf sheath was usually greater, and never less, in E() than in E(-) plants. The leaf rolling and stomatal conductance resul ts suggest that E(-) plants were more severely stressed in the summer after planting. Thus, the endophyte may induce greater water retention in the leaf sheath and therefore better protect the internal growing zone from lethal desiccation.