Evaluation of Drought Tolerance of Indeterminate Soybean Genotypes in Flowering and Seed Filling Stages

Water deficiency is the first limiting factor in soybean production in semi-arid regions. Therefore, increasing soybean grain yield requires selection of resistant and adapted genotypes to dry or water deficit conditions of Iran. In this investigation, in order to evaluate the drought tolerance of indeterminate soybean genotypes, an experiment was performed using factorial based on a completely randomized design with three replications. The experimental factors included six genotypes of soybean and three levels of drought stress (control, flowering and seed filling stages). Six drought tolerance indices of MP, GMP, TOL, SSI, STI and HARM were assessed on the basis of grain yield in stress and non-stress conditions. Stress intensity for the flowering stage was low (SI =0.291) while it was high for seed filling stage (SI =0.429). Based on the results of principal components, two first components totally explained 99.9% of variation among the data. The first and second components were named drought tolerance and stress susceptibility component respectively. Based on the results of correlation between drought resistance indices and grain yield in stress and non-stress environments, indices of MP,GMP, HARM and STI were recognized as best for selection of tolerant genotypes. Based on the bi-plot graph, cultivars Williams and Hack in flowering stage and cultivar Williams in seed filling stage were recognized as tolerant cultivars.