Effects of high‐temperature stress on microsporogenesis in heat‐sensitive and heat‐tolerant genotypes of Phaseolus vulgaris

High ambient temperature (32/27 °C, day/night, 12 h photoperiod) applied prior to anthesis to Phaseolus vulgaris plants results in abnormal pollen and anther development during microsporogenesis. Scanning and transmission electron microscopy were used to examine anther and pollen morphology and pollen wall architecture after heat stress was applied to two genotypes that differ with respect to yield potential under high‐temperature field conditions: one, a heat‐sensitive, Mesoamerican genotype, A55, the second, a heat‐tolerant, Andean genotype, G122. High‐temperature treatment of both genotypes was applied 1–13 d before anthesis. Under heat stress, the heat‐tolerant genotype showed anther and pollen characteristics that were generally similar to the low temperature controls. In contrast, after 9 d of heat treatment before anthesis, the anthers of the heat‐sensitive genotype were indehiscent and contained abnormal pollen. Pollen wall architecture was also affected in the 12 and 13 d treatments. In addition to the morphological changes, the heat‐sensitive genotype also experienced reduced pollen viability and reduced yield in high‐temperature experiments conducted in both the greenhouse and field.