Heat Tolerance of Kentucky Bluegrass as Influenced by Pre- and Post-Stress Environment

An understanding of the natural variation in heat tolerance of Kentucky bluegrass is needed to develop predictive models for stress tolerance. The variation in heat tolerance of ‘Adelphi’ Kentucky bluegrass (Poa pratensis L.) over the growing season and the effect of recovery environment on the perceived heat tolerance of the plants was determined. Field-grown plants (Chillum silt loam, fine-silty, mixed, mesic Typic Hapludults) were exposed to heat stress on 11 dates over two growing seasons by immersion in a water bath for 30 min at either 42, 44, or 46°C and then placed in either a greenhouse, or one of two growth chamber environments (35/22 or 22/15°C day/ night temperature) for a 2-week recovery period. The dry weight of the stressed plants expressed as a percentage of the controls (recovery weight) was used as a measure of heat tolerance. Heat tolerance increased from May to July and then decreased from August to October. A significant relationship existed between heat tolerance, day length (D) and average low temperature (LT) for the sampling dates (y - 128.65*D - 5.67*D2 - 14.46*LT - 0.49*LT2 + 2.21*D*LT - 743.86, R2 = 0.95, P = 0.003). Recovery weights for plants in the greenhouse were not significantly different from recovery weights for plants in either of the other two recovery environments on 10 of the 11 sampling dates