High temperature effects on pod and seed production as related to hormone levels and abscission of reproductive structures in common bean (Phaseolus vulgaris L.)

Pod and seed numbers of Phaseolus vulgaris L. were markedly reduced by exposure to a high temperature (HT) of 32 27°C (day/night) for 5 days at anthesis. The reduction was caused by an increased abscission of flower buds, flowers and young pods, and by the failure of fertilization and seed development. Bean cultivars differed in their heat tolerance, as indicated by the relative decrease of pod and seed numbers at HT, compared with control plants at 22 17°C. HT decreased the amounts of indol-3yl-acetic acid (IAA) exported to agar (exp-IAA) from flower buds, flowers or young pods. This effect was more pronounced in the flowers. A positive correlation (R = 0.922) was observed between the relative (%) adverse effects of HT on pod number and on exp-IAA from flowers, i.e. cultivars with a higher tolerance to HT of pod production had a smaller relative reduction in exp-IAA. No consistent relationships were found between the effects of HT on abscisic acid (ABA) levels and on yield parameters, or between ABA and exp-IAA.