عنوان مقاله [English]
Common bean is the most important food legume and is an important source of calories, protein, dietary fiber, and minerals. In addition, common bean provides an essential source of protein for more than 300 million people worldwide. Drought is the major constraint to common bean production, resulting in significant yield reductions of 60% of global bean production areas. In addition, competition among crops for production area in certain regions has resulted in a shift of dry bean production to more marginal zones associated with increased abiotic stresses such as water stress and heat. Robust drought tolerance is conferred by traits that result in stable yield in the presence of water stress, as opposed to mechanisms of escape, such as early maturity. The evaluation and selection for drought tolerance should therefore be focused on the selection of traits that directly affect yield under stress conditions. The objective of this study was recognition of the reaction of bean genotypes and identifies tolerant genotypes to water stress in East Azarbaijan region, Iran.
Materials & Methods
The experiment was carried out during 2011 cropping season in Azarshahr- East Azarbaijan, Iran. The experimental site was located at 1370 m asl and with sandy loam soil receives an annual average rainfall of 300 mm. Plant material consisted of nine genotypes of red, white and wax bean were provided from Khomein national bean research center. Genotypes were evaluated separately in a randomized complete block design under irrigation and water stress conditions. Each genotype was planted on a plot made of five rows of 3 m length with a row-to-row distance of 0.5 m and a plant-to-plant spacing of 5 cm. Irrigations in normal and drought stress conditions were applied after 70 and 100 mm evaporation from class A pan. Days to flowering and to maturity, plant height, shoot diameter, seeds in plant and in pod, pods in plant, 100 seed weight and seed yield traits were recorded. For identifying suitable bean genotypes, multiple drought tolerance and sensitivity indices were calculated. Orthogonal comparisons were used to compare bean genotypes for seed yield based on their colors in normal irrigation and water stress condition. Because irrigation effect was significant in combined analysis, so analysis of variance was performed separately for each set of experiment.
Results & Discussion
Analysis of variance showed that there were significant differences among genotypes in both irrigation conditions for all traits. Water stress led bean genotypes to mature 12 days earlier and the greatest reduction was found 22 days in wax bean genotypes. The plant height reduction under water stress condition in both groups of bean was roughly equal. Orthogonal comparison of bean genotypes for seed yield based on their colors in normal irrigation and water stress condition showed wax bean genotypes were the best in two conditions and had more yield. The results showed that water stress decreased the yield of genotypes up to 47 percent. The response of bean genotypes was different for water stress and lowest and highest yield loss was observed for wax and white beans genotypes, respectively. Correlation coefficients between the normal irrigation and water stress condition were positive and highly significant for seed yield. The presence of strong correlation between yields of water stress and non-stress conditions indicated that genotypes which were performed under non-stress conditions also performed under water stress growing conditions. The results showed suitable bean genotypes can be identified with considering yield of genotypes in both conditions. Drought tolerance indices namely geometric mean (GMP), stress tolerance (STI) and arithmetic mean (MP) were better than others indices for tolerant bean genotype selecting.
Drought stress decreased yield and its components in bean genotype, but the reaction of genotypes were different. The findings suggesting that, selection based on the absolute performance of the genotypes across environments is more successful than selecting across the minimum yield decrease under stress with respect to favorable condition. In water stress condition, wax bean genotypes were better than red and white bean genotypes. Between wax bean genotypes, genotypes GO140 was the superior and can be considered as best for similar climate conditions