Cell Membrane Thermostability and Whole‐Plant Heat Tolerance of Kentucky Bluegrass

Abstract

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.