DIFFERENTIAL SENSITIVITY TO HIGH-TEMPERATURE OF STAGES IN THE REPRODUCTIVE DEVELOPMENT OF COMMON BEAN (PHASEOLUS-VULGARIS L)

The effects of high temperature (HT: 32/27-degrees-C) on different stages of reproductive development in common bean were studied in two determinate cultivars (PI-271998 and BBL-47). Plants grown at 22/17-degrees-C were exposed to short periods (1 or 5 days) of 32/27-degrees-C at micro- and macrosporogenesis, pollen and embryo-sad development, anthesis and early pod and seed development. Effects of HT on male and female development were assessed by light and scanning microscopy, pollen stainability, pollen tube growth, and pod and seed set. Sensitivity to HT changed with flower development. Post-fertilization stages and early pod development were more tolerant to HT than prefertilization stages. Exposure to HT at sporogenesis results in male sterility due to non-viable pollen and failure of anther dehiscence, whereas gynoecium function was unaffected. During later stages, HT reduced pollen tube penetration into the stigma, resulting in lower pod and seed set, especially in the more HT-sensitive BBL-47. Changes in the sensitivity of male and female parts to HT showed opposite trends. While pollen sensitivity to HT decreased with pollen maturation, the negative effect of HT on the function of the gynoecium was greater at anthesis. Reduction of ovule fertilization and seed set by HT were larger at the positions furthest from the stigma and closer to the peduncle, and probably reflect HT constraints to pollen tube growth. It is concluded that the lower pod and seed set after exposure of common bean plants to HT is the combined result of both lower pollen viability and impaired female performance in a large proportion of the flowers.