IMPROVING COMMON BEAN PERFORMANCE UNDER DROUGHT STRESS

Drought is the second major constraint to common bean (Phaseolus vulga ris L) production after disease. This study examined yield under droug ht, yield potential, drought susceptibility index, harvest index, and geometric mean as potential indicators of drought resistant genotypes. The performance of two common bean populations, consisting of 78 and 95 recombinant inbred lines, was examined under moisture stress and no nstress regimes. Experiments were conducted at seven locations (1990-1 994) in Michigan and Mexico to identify effective selection criteria f or drought resistance. Two genotypes from each population yielded in t he top 10% under both stress and nonstress conditions. Heritability es timates for yield in the Sierra/AC1028 population, based on 5 yr of da ta, ranged from 0.55 to 0.59 for stress and nonstress, respectively, a nd from 0.20 to 0.19 for stress and nonstress, respectively, in the Si erra/Lef-2RB population. Heritability for plant biomass was 0.52 for s tress and 0.55 for nonstress in the Sierra/AC1028 population and 0.15 under stress and 0.05 under nonstress in the Sierra/Lef-2RB population . One-hundred seed weight was the most highly heritable trait in both populations with heritability estimates of 0.80 for the Sierra/AC1028 population and 0.65 for the Sierra/Lef-2RB population. The geometric m ean of the two moisture regimes was the single strongest indicator of performance under stress and nonstress, and a breeding strategy that i nvolves selection based first on the geometric mean, followed by selec tion based on yield under stress, was suggested as the most effective strategy to improve drought resistance in common bean.