evaluation of the effects of late season water stress on genotypes of bean (phaseolus vulgaris l.)

introduction common bean (phaseolus vulgaris l.) is the world’s most important food legume. this staple is considered as a nearly perfect food mainly because of its high protein content and abundant fiber, complex carbohydrates, and other daily food needs such as vitamins (folate) and minerals (cu, ca, fe, mg, mn, zn). annual production, including both dry and snap bean, exceeds 21 million metric tons (mt), which represents more than half of the world’s total food legume production. a majority of the bean production occurs under low input agriculture on small-scale farms in developing countries. beans produced by these resource-poor farmers are more vulnerable to attack by disease and insect pests and to abiotic stresses including drought and low soil fertility. development of cultivars with improved resistance to biotic and abiotic stresses is a primary goal of bean breeding programs throughout the world. as much as 60% of common bean (phaseolus vulgaris l.) production in the developing world occurs under conditions of significant drought stress. selecting drought tolerant genotypes, could be a viable option to cope with the limited available water for irrigation and increasing the productivity in such climates. terminal drought is one of the main water limiting conditions that constrain common bean production because plants rely on the stored soil water during flowering and pod-filling periods, when usually water deficit intensifies. materials and methods to evaluate of the effects of late season water stress on phenological traits, grain yield, yield components, determination of phenotypic variation and evaluation of relationship between grain yield with other traits in 33 bean genotypes an experimental design was carried out using a randomized complete block design with three replications under two conditions (stress and non-stress) in 2012 in the experimental field of college of agriculture and natural resources of tehran university in karaj campus. results and discussion results showed that among genotypes in study traits there were significant differences which reveal genetic variation among the genotypes. the highest and lowest grain yield in non-stress condition was in 28 and 12 number genotypes, respectively. the highest and lowest grain yield in stress condition was in 14 and 25 numbers of genotypes, respectively. the analysis of tolerance index correlation showed that indices of tolerance stress (sti), mean productivity (mp) and geometric mean productivity are the best indices for identifying genotypes with high yield in both conditions. according to the results of phenotypic correlations, stepwise regression, path analysis in both normal and stress conditions, it can be concluded that, the traits of biological yield, seed and pod weight, number of filled pods, number of seeds per plant, 100 seed weight and number of seed per pod were the most important and effective traits on yield. according to principal component analysis using seven agronomic traits in both conditions, two main components were selected that in total under non stress condition 72 percent and under water stress condition 76 percent of the total variation was explained and in both conditions, the first and second factors were introduced as yield and yield component factors. conclusions in crops such as common bean, where seeds are the product of interest, the main criteria for selection of agronomical resistance to drought is focused on traits that lead to a higher grain production. followed by selection based on yield under stress, was suggested as the most effective strategy to improve drought resistance in common bean. it is suggested that selection under stress reveals that some of genotypes have resistant inherited genes, and are key to yield improvement of common bean. cultivars with improved stress resistance can reduce reliance on pesticides in high input systems, avert risk of yield loss from pests in low- and high-input systems, and enable more stable bean production across diverse and adverse environments (low precipitation, high humidity, etc.) and poor soil conditions (low fertility, hillsides, etc.). this study reinforces the importance of characterizing drought resistant genotypes selected for particular drought types, to build a better picture of those mechanisms involved in drought resistance during specific plant developmental stages and to particular environments, knowledge that will contribute to define selection criteria for drought resistance in common bean that, after proper validation, could be used in improvement programs.