Identification of key agronomical traits contributing to the selection of superior lines of soybean in Moghan Plain

Soybean is a valuable industrial plant worldwide because of its high protein content, high quality unsaturated oil, and many direct and indirect uses. Seed yield is determined by many vegetative and reproductive traits in different amounts. In some cases, the improvement of a specific trait is accompanied by simultaneous changes in one or more other traits, which provides the possibility of using indirect selection. This study aimed to investigate the correlation between phenotypic traits and yield components, propose cause-and-effect relationships for grain yield components, and determine the direct and indirect effects of traits on soybean seed yield. In this study, 13 pure lines obtained from breeding programs with two control varieties, Amir and Saba, were cultivated during the agricultural year of 2019/2020 at the Agricultural and Natural Resources Research Center of Ardabil (Moghan). The experimental arrangement was a randomized complete block design with three repetitions. Correlation coefficients were used to understand the relationships between traits, path analysis was used to estimate the direct and indirect effects of traits on seed yield, and factor analysis was used to explain the correlation between variables and selection of the desired lines was done using factor analysis and cluster analysis. Based on the results of variance analysis for testing differences in composite variables, the genotypes had significant differences in terms of vegetative traits, yield components, and seed yield. Correlation between phenotypic traits showed that the number of nodes per plant was positively and significantly correlated with the number of pods per plant and the number of seeds per plant. In addition, the correlation of the number of seeds per plant with seed yield was positive and significant (r=0.76**). The results of path analysis showed that traits related to the number of seeds per plant, such as the number of pods per plant, showed a high direct and indirect correlation with seed yield. The direct effect of seed number on yield was positive (0.66), whereas the weight of one hundred seeds had a high negative direct effect (-0.44) on seed yield and a positive indirect effect through the number of days to flowering (0.24). Factor analysis showed that the first factor justified 41.2 of the total variation, and the highest positive factor coefficients belonged to plant height, number of nods, total pods and number of seeds per plant. The second factor explained 21.78% of the total variation, day to of flowering, days to maturity, number of branches per plant and one hundred seed weight had the highest coefficients. Factor analysis was able to identify high yielding and earliness lines, which were placed in group 2 of cluster analysis. Factor analysis showed that four factors explained 62.98% of the total variance. According to path analysis, among the yield components, the number of seeds per plant has the largest contribution in determining the yield, and the trait of the number of pods per plant, which causes the production of more seeds in soybean lines, should be prioritized in breeding programs and selection of superior lines. Lines G14, G5, G2, G10 and G8 were placed in the group of lines with high performance and early maturity groups.