Pod harvest index as a selection criterion to improve drought resistance in white pea bean

Common bean (Phaseolus vulgaris L) is an important food legume grown in Africa and Latin America, where water deficits frequently reduce grain yield. The objectives of this study were to identify advanced lines of common bean with superior seed yield under drought, and to identify plant traits that could serve as selection criteria for evaluating drought resistance. Seventy-eight advanced inbred lines (genotypes) were generated by single seed descent and evaluated with the two parents (ICA Bunsi, a white pea bean variety and SXB 405, a breeding line) and a standard check (Awash melka) under drought and irrigated field conditions in 2008 and 2009 at Melkassa, Ethiopia. Seed yield, seed number per m(2), pod number per m(2) and 100 seed weight were reduced by 65%, 34%, 29% and 12%, respectively under drought stress compared to irrigated conditions. Two genotypes (G87, G80) had better drought yield compared with a standard check, and several also responded to irrigation. Pod harvest index (PHI; [dry weight of seed/dry weight of pod at harvest] x 100) was reduced in sensitive genotypes and increased in resistant genotypes under drought stress conditions indicating the importance of remobilization of photosynthates from pod wall to seed. Principal component analysis indicated that the first component including five traits (grain yield, seed number per m(2), pod number per m(2), 100 seed weight and PHI) explained 35.7% of the total variation under drought stress. Correlations of PHI with yield (0.43***) and fair heritability (0.48) in drought suggest that PHI would be an effective selection criterion for identifying genotypes with improved drought resistance. Correlated gain in drought yield from selection for PHI would be greater than direct yield selection, due to much better heritability of PHI, and would also contribute to irrigated yield. (C) 2013 Elsevier B.V. All rights reserved.