TRAITS RELATED TO DROUGHT RESISTANCE IN COMMON BEAN

Common bean (Phaseolus vulgaris L.) is grown in regions where water de ficits during reproductive development significantly reduce yield. The purpose of this study was to evaluate the association of specific phe nological and physiological traits with drought resistance in common b ean. Five genotypes were grown under and near a rain shelter in 1988, and an additional 16 progeny lines were included in 1990. Drought stre ss determined by the drought intensity index was severe (0.78) in 1988 and more moderate (0.63) in 1990. Water stress reduced the expression of most traits with the exception of days to flower and leaf moisture retention capacity. Seed yield among genotypes was reduced from 22 to 71% due to drought. Yield under stress was correlated with yield unde r nonstress in 1990 and negatively correlated with the drought suscept ibility index in 1988. Yield components which exhibited the largest di fferential genotypic responses to stress were pod and seed number, whe reas seed size was more stable. Genotypic variation was detected in al l the partitioning indexes, chiefly harvest index and relative sink st rength, and the heritability estimates for these traits were high. The limited genetic variability observed among water relations traits and their role in water conservation would restrict their potential use i n the selection for drought resistance in common bean. The differentia l correlations between phenological, biomass and partitioning traits a nd the indexes for yield and drought susceptibility would suggest that the most effective approach in breeding for drought resistance in com mon bean would be based first on selection for high geometric yield fo llowed by selection among the high-yielding individuals for low to mod erate levels of the drought susceptibility index.