CELL-MEMBRANE THERMOSTABILITY AND WHOLE-PLANT HEAT TOLERANCE OF KENTUCKY BLUEGRASS

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