Physiological responses of Festuca arundinacea to fungal endophyte infection

Enhanced growth rates of several grass species infected by fungal endophytes are known, but the underlying changes in plant physiology are not. Carbon exchange rates (CER) and leaf conductances (g) of 13 genotypes of tall fescue (Festuca arundinacea Schreb, var. KY 31) infected by the fungal endophyte Acremonium coenophialum Morgan-Jones and Gams were measured at ambient conditions. Endophyte-free ramets of the same genotypes were also measured. Correlations were calculated between environmental conditions at the time of measurement, and physiological responses. The only differential response of infected and uninfected ramets was to temperature. At low leaf temperatures no difference was seen between infected and uninfected plants. However, at leaf temperatures above 35 degrees C infected tall fescue plants photosynthesized at a significantly greater rate (20-25%) than uninfected plants. This resulted from a decrease in the CER of uninfected plants, not an increase in the rate of infected plants, at high temperature. There were also significant infection x genotype interactions, indicating that the response to infection was specific to a given genotype. These results indicate that physiological responses of host plants to fungal endophyte infection depend both on the physical environment and the genotype of the plants.