Drought avoidance characteristics of diverse tall fescue cultivars

In recent years, turf type tall fescues (Festuca arundinacea Schreb) are being used for northern to mid-South climates in the US. Limited information is available on the diversity among cultivars of drought resistance and avoidance characteristics, which are important for persistence under drought and high-temperature stresses. Four cultivars ('Rebel II', 'Rebel Jr', 'Kentucky 31', 'Bonsai') and 'GA-5' as endophyte-free (EF) and endophyte-infected (EI) with Acremonium coenophialum Morgan-Jones and Gams were evaluated in a field study at Griffin, GA, (using n clayey, kaolinitic, thermic Typic Hapludult soil) for intraspecific differences in overall drought resistance and for drought avoidance characteristics. These grasses provided a range in morphological traits. Overall drought resistance ranking based on decline in turf quality, leaf firing (LF), and/or wilt expression during dry-down was Rebel II (best) > Rebel Jr, Kentucky 31, GA-5-EF, GA-5-EI > Bonsai. The magnitude of differences in drought avoidance characteristics among cultivars (least cultivar = 100% base) for each year, respectively, were 213 (1991) to 200% (1992) for late summer root length density (RLD) at 20- to 60-cm depth; 182 (1991) to 173% (1992) for total root length (TRL) in late summer; and 1237% for evapotranspiration (ET) averaged over all water use periods (ie, 1991 and 1992). Field measured ET rates revealed much lower ET rates (33-73% less) for the combination of humid climate and mild drought stress than reported in the literature for semi-arid/arid and well-irrigated tall fescue. Additionally, multiple regression analysis demonstrated that high RLD (20- to 60-cm depth) was associated with less LF and wilt; maintenance of ET at 4 to 8 d after irrigation was related to less LF; and high RLD (3- to 10-cm depth) related to greater LF and wilt. This suggests that high RLD in the deeper root zone and the ability to maintain ET as the soil dries are important for drought resistance of tall fescues.