PHYSIOLOGICAL-RESPONSES OF FESTUCA-ARUNDINACEA TO FUNGAL ENDOPHYTE INFECTION

Enhanced growth rates of several grass species infected by fungal endo phytes are known, but the underlying changes in plant physiology are n ot. Carbon exchange rates (CER) and leaf conductances (g) of 13 genoty pes of tall fescue (Festuca arundinacea Schreb, var. KY 31) infected b y the fungal endophyte Acremonium coenophialum Morgan-Jones and Gams w ere measured at ambient conditions. Endophyte-free ramets of the same genotypes were also measured. Correlations were calculated between env ironmental conditions at the time of measurement, and physiological re sponses. The only differential response of infected and uninfected ram ets was to temperature. At low leaf temperatures no difference was see n between infected and uninfected plants. However, at leaf temperature s above 35 degrees C infected tall fescue plants photosynthesized at a significantly greater rate (20-25%) than uninfected plants. This resu lted from a decrease in the CER of uninfected plants, not an increase in the rate of infected plants, at high temperature. There were also s ignificant infection x genotype interactions, indicating that the resp onse to infection was specific to a given genotype. These results indi cate that physiological responses of host plants to fungal endophyte i nfection depend both on the physical environment and the genotype of t he plants.