Decrease of pollen stainability of green bean at high temperatures and relationship to heat tolerance

Pod yield of 'Kentucky Wonder' green bean (Phaseolus vulgaris L.) decreased at high temperatures due to a reduction of pod set. A highly positive corr elation was observed between pod set and pollen stainability in flowers tha t were affected by heat stress about 10 days before anthesis. Pollen staina bility was decreased by heat stress applied 8 to 11 days before flowering u nder controlled environment conditions. When mean air temperature during th is period exceeded 28 degreesC, pollen stainability decreased under field c onditions. Low pollen stainability indicated sensitivity to high temperatur es about 10 days before flowering. A heat-tolerant cultivar showed higher p ollen stainability than did heat-sensitive cultivars under high temperature s. These results demonstrated that heat tolerance at an early reproductive stage could be evaluated by analyzing pollen stainability using flowers dev eloped under high temperatures.