Physiological responses of diverse tall fescue cultivars to drought stress

Drought is among the most limiting factors for turfgrass growth. Understanding genetic variations and physiological mechanisms in turfgrass drought resistance would facilitate breeding and management programs to improve drought resistance. The experiment was designed to investigate shoot physiological responses of six tall fescue (Festuca arundinacea Schreb.) cultivars representing several generations of turfgrass improvement to drought stress. Grasses were grown in well-watered or drying (nonirrigated) soil for 35 days in the greenhouse. Net photosynthetic rate (P(n)), stomatal conductance (g(s)), transpiration rate (Tr), relative water content (RWC), and photochemical efficiency (Fv/Fm) declined during drought progression in all cultivars, but the time and the severity of reductions varied with cultivar and physiological factors. The values of P(n), RWC, g(s), and Tr decreased significantly for 'Rebel Jr', 'Bonsai', and 'Phoenix' when soil water content declined to 20% after 9 days of treatment (DOT) and for, 'Houndog V', 'Kentucky-31', and 'Falcon II' when soil water content dropped to 10% at 15 DOT. A significant decrease in Fv/Fm was not observed in drought-stressed plants until 21 DOT for 'Rebel Jr', 'Bonsai', and 'Phoenix' and 28 DOT for 'Houndog V', 'Kentucky-31', and 'Falcon 11'. The decline in P(n) resulted mainly from internal water deficit and stomatal closure under mild drought-stress conditions. After a prolonged period of drought stress (35 DOT), 'Falcon II', 'Houndog V', and 'Kentucky-31' maintained higher P(n) than did 'Rebel Jr', 'Bonsai', and 'Phoenix', which could be attributed to their higher Fv/Fm. This study demonstrated variation in drought resistance among tall fescue cultivars, which was related to their differential responses in photosynthetic capacity and water relations.