Effect of the Tall Fescue Endophyte on Plant Response to Environmental Stress

Abstract The adverse effect of the tall fescue ( Festuca arundinacea Schreb.) fungal endophyte ( Acremonium coenophialum Morgan‐Jones and Gams) on animal performance is well recognized but the mutualistic effect of this fungus‐grass association under environmental stress is not well understood. The objective of this study was to evaluate endophyte‐free (EF) and endophyte‐infected (El) tall fescue plants from one clone for morphological and physiological responses to flooding, N rates (11, 73, and 220 mg N pof −1 ), and −0.03, −0.05 and −0.50 MPa drought stress in the greenhouse. Plants were grown in a synthetic mixture of the following by volume: Cecil sandy clay loam (clayey, kaolinitic, thermic Typic Hapludult) (33%), sand (16%), peat moss (17%), perlite (17%), and vermiculite (17%). Leaf blades of El, as compared to EF plants were thicker and narrower regardless of flooding, N rate, or drought stress. Plant ultrastructure was not appreciably altered by the endophyte. Herbage growth was 50% greater on El than EF plants, especially at higher N levels. Tillering increased on El plants but only at the highest N rate. The El plants were more productive than EF plants at mild soil moisture stress (−0.05 MPa). At more severe stress (−0.5 MPa) 75% of EF plants died and all El plants survived. Leaf rolling under drought stress was much more common in El than EF plants. Regrowth after harvest with abundant watering of previously drought‐stressed plants was much greater on El than EF plants. There was little or no difference in digestibility of forage from El and EF plants. The results indicate that there are positive benefits derived from association of an endophyte with tall fescue resulting in growth stimulation, improved survival, and drought tolerance to the host plant that could be important in plant competition.