SELECTION CRITERIA FOR DROUGHT-RESISTANCE BREEDING IN TURFGRASS

Cumulative evapotranspiration (ET(cum)) patterns of 10 commercially available cool-season turfgrass species and cultivars were evaluated under progressive water stress in the semi-field conditions using a gravimetric mass balance method in three studies. At the end of water stress, the cultivars were visually scored for green appearance on a 0 (no green) to 10 (100% green) scale. A Gompertz nonlinear model gave a best fit to ET(cum) vs. days adjusted for pan evaporation variation. Two of the ET(cum) attributes (t(i), the time during which the rate change ET is zero, and ET(max) the maximum ET rate) estimated from the Gompertz model appeared to reflect efficient water-use attributes in theturfgrass. Among the physiological screening techniques studied, electrolyte leakage, relative water content, and the difference between canopy and air temperature appeared to separate cultivars by drought resistance and water use efficiency (WUE). These physiological attributes were also relatively easy to measure and had high correlations with color score and WUE. Biplot display is a graphical technique in which the interrelationships between the cultivars and water-use attributes can be displayed together. Based on t(i), ET(max), color score, and physiological attributes, 'Wabash' and 'Bristol' Kentucky bluegrass (Poa pratensis L.), 'Aurora' hard fescue (Festuca ovina var. duriuscula L. Koch.), and 'FRT-30149' fine fescue (F. rubra L.) were identified as cultivars with higher WUE.