Acremonium coenophialum-mediated short- and long-term drought acclimation in tall fescue

The mutualistic association between Acremonium coenophialum Morgan-Jones and Gams and its tall fescue (Festuca arundinacea Shreb.) host provides plant scientists with unique opportunities to create superior turf and forage cultivars. The objectives of this research were to determine endophyte-mediated drought acclimation in tissue-cultured regenerants of tall fescue containing one of three A. coenophialum isolates during short- and long-term drought stress. Two experiments were conducted by growing vegetative propagules of plants with endemic or introduced endophytes in 120-L tubs containing fritted clay: one experiment examined water relations during a 15-d drought period and the other during a 70-d water stress period. Leaf water potential and turgor pressure responses to soil water content differed among infected and non-infected plants, among endophytes inserted within a plant genotype, and among plant genotypes containing a common endophyte during 15 d of stress. Among endophytes, only EDN11 induced acclimation to 70 d of stress when inserted into plant genotype PDN2. Leaf water potential and turgor pressure were approximately 0.50-0.75 MPa greater when PDM was infected with EDN11 compared to other endophytes during the 70 d of stress. Endophyte had no effect on leaf osmotic potential and minimal effect on plant water soluble mineral and sugar concentrations, and endophyte-mediated adaptation to drought stress was an avoidance mechanism. Because enhanced drought tolerance is a result of specific interactions between plant genotypes and endophyte isolates, selection of endophytes specifically for enhancing drought tolerance in tall fescue is not likely to have a general effect on the plant population.