Cell membrane thermostability and whole-plant heat tolerance of Kentucky bluegrass

Heat stress is often a major problem in C₃ (cool-season) turfgrasses during summer months, resulting in reduced turf quality and stand loss. Current germplasm screening for heat tolerance relies on field and whole-plant techniques, which are often inefficient and insensitive due to environmental interactions. A rapid, accurate procedure allowing simultaneous screening of large numbers of genotypes is needed. In vitro cell membrane thermostability (CMT) has been determined for a number of plants. The objectives of this study were to determine if differences in CMT exist among cultivars of Kentucky bluegrass (Poa pratensis L.), and if CMT can predict whole-plant heat tolerance of these cultivars. CMT was determined by subjecting leaf segments to progressive heat shock exposure times, and deriving cellular electrolyte leakage curves. Whole-plant heat tolerance was determined by subjecting plants to 41°C day/34°C night at 95% relative humidity for 62 d (Study 1) and 47 d (Study 2) in controlled-environment chambers. Relative percentage leaf firing and percentage shoot dry weight were determined weekly. CMT was negatively correlated with relative percentage leaf firing (r = -0.80) and positively with relative percentage shoot dry weight (r = 0.75), averaged over two experiments. CMT and whole-plant heat tolerance used as indicators demonstrated that cultivars BM-3 and Midnight were more heat tolerant than Lavang, Nugget, and Ryss. This is the first report showing that CMT can predict whole-plant heat tolerance among turfgrass cultivars. Being rapid, accurate, and requiring little space, CMT may offer turfgrass breeders an ideal method for screening large numbers of genotypes for heat tolerance.