Morphophysiological Responses of Common Bean (Phaseolus vulgaris L.) Genotypes to Water Stress

Yield of common bean (Phaseolus vulgaris L.) is highly constrained by water deficit especially when this occurs during the reproductive development. The purpose of the study was to determine the association of the morphophysiological traits with water stress and how this affects grain yield in common beans. A field experiment involving eight common bean genotypes and three water regimes (50 %, 75 %, and 100 % of crop evapotranspiration) was conducted at National Irrigation Research Station, Mazabuka district during the 2012 growing season. A Split plot design with four replications was used; with soil moisture regime (main plot) and the genotypes (subplot). Based on variation in water stress tolerances, 8 test genotypes - Gadra, KE 3, KE 4, ZM 4488, SER 76 SER 180, SER 89 and CAR-ZAR were used. Water stress treatments were imposed at pre-flowering stage and was discontinued after 43 days when the crop was in its late reproductive stage. Significant differences were found among genotypes for Chlorophyll a (Chl a), Chlorophyll b (Chl b), Total Chlorophyll, Relative water content, Grain yield, Number pods per, Seed weight, Seeds per pod and Days to 50 % flowering under the three water stress conditions. The grain yield in normally irrigated condition (2191.3 kg ha-1) was 60 % higher than in high water stress condition (866.2 kg ha-1), while in the low water stress condition (1078.3 kg ha-1), the reduction in grain yield was 50.8 %. There were significant genotype by environment showing that the genotypes behaved differently under the different growing conditions. Results suggested that Gadra, KE 4, ZM 4488, and SER 180 were water stress tolerant while the SER 89, CAR-ZAR, KE 3 and SER 76 were water stress sensitive genotypes. These results suggest that a selection method based on 100 SW, Chl a, Chl b, and NPP can be used in breeding for bean genotypes to water stress.