| Endophyte (Acremonium coenophialum Morgan-Jones and Gams) infection enhances drought tolerance of tall fescue (Festuca arundinacea Schreb.); however, the mechanisms of enhancement are poorly understood. The objective was to investigate the relation between endophyte infection and changes in tall fescue growth, water potential, leaf conductance, and solutes in response to drought.;Endophyte presence had no consistent effect on leaf elongation rate in growth chamber or in field studies. Drought stress increased leaf growing zone and leaf sheath dry weight, fructan, and sucrose concentrations while hexose concentration was decreased. Endophyte infection tended to decrease fructan concentration in the growing zone and lower leaf sheath. The most consistent effect of endophyte was an increase in the water content of the lower sheath under well-watered conditions compared with noninfected plants. This was generally accompanied by a reduction in sheath dry weight. Under mild drought stress, differences in sheath water content between endophyte-infected and endophyte-free plants were reduced in the field or disappeared in growth chamber studies In conclusion, the water relations of the leaf sheath rather than of the growing zone are changed by endophyte infection under well-watered and mild drought stress conditions.;Endophyte-free plants showed more leaf rolling than endophyte-infected plants during drought in the first year after establishment in a field study. On at least one occasion, proline concentration was higher and water potential was lower in drought-stressed, endophyte-infected plants compared with endophyte-free plants. Endophyte-free plants also tended to have a lower stomatal conductance under well-watered conditions. Endophyte-free plants apparently had a less developed root system in the first year after establishment than endophyte-infected plants.;When plants were grown in dishpans in competition for the same soil water supply, endophyte-infected tillers showed a higher survival rate after severe drought and greater growing zone water content than did endophyte-free tillers. In conclusion, mechanisms other than increased root growth were responsible for endophyte-enhanced drought survival. Reduced stomatal conductance during progressive drought stress could have contributed to endophyte-enhanced drought survival. |
