Evaluation of drought and heat tolerance of common bean (Phaseolus vulgaris L.)

The aim of this work was to evaluate drought and heat tolerance of differen t bean varieties (Phaseolus vulgaris. L) at two stages of development (vege tative and flowering) to understand the physiological aspects of drought to lerance between varieties. Local Egyptian bean varieties (Giza3 and Giza6) and varieties introduced to Egypt (Bronco, Flexo, and Tema) were subjected to water stress at seedling and flowering stages by withholding water for 6 days. The experiments were conducted in a well controlled greenhouse at th e research station of the Institute for Vegetable Science at Durnast, Bavar ia, Germany. Leaf water potential, stomatal conductance and chlorophyll con tent were measured during water stress in addition to yield measurements. A nother group of plants from the same varieties were subjected to high tempe rature (32 OC) for 8 days but kept well-watered to avoid water stress. Phot osynthetic rate and stomatal conductance were measured at the end of heal s tress. Giza3 and Flexo varieties maintained higher leaf water potential, lo wer stomatal conductance during water stress and had higher yield than the other varieties. At the end of the heat stress period, Giza3 and Flexo had a higher photosynthetic rate and higher stomatal conductance which helped t o maintain higher photosynthesis. The results indicate that Giza3 and Flexo varieties had relatively better control of stomata during water stress whi ch allowed them to postpone the dehydration with consequently higher stabil ity for heat stress.