Water Stress Tolerance of Common Bean (Phaseolus vulgaris L.)

Drought is a world wide production constraint of Common bean. The effective approach in breeding for drought tolerance in common bean would be based first on selection for high geometric yield followed by high-yielding individuals for low to moderate levels of the drought susceptibility index. The tolerant genotypes had less affected leaf area and shoot dry weight, greater root weights and higher root/shoot ratios and less degradation chlorophyll contents than the drought susceptible genotypes. The yield reduction was caused by water stress attributed mainly due to reduction in pods plant-1. The high relative water content, minimal midday drop of relative water content, lower water uptake capacity and low rate of transpiration may probably enable plant to maintain a high water content in leaf cells under drought condition. The drought avoidance included the development of better root characteristics, an efficient stomatal closure and paraheliotropic leaf movement that altogether regulated water balances more in the tolerant genotypes. The mechanism of drought tolerance included osmotic adjustment and protection of membrane system.