Evaluation of response to direct and indirect selection of agronomic and reproductive stages characteristics in Water deficiency stress conditions conditionin soybean (Glycine max L.)

Selection efficiency requires complete and accurate knowledge of genetic parameters such as heritability, phenotypic and genotypic variation coefficient, environmental variance, selection response, genetic gain, genetic and phenotypic variance, genetic and phenotypic correlation between traits that the breeder consciously chooses the appropriate selection method in breeding populations. In this study, some genetic parameters for yield and soybean agronomic and reproductive period characteristics under normal and stress conditions were estimated and drought tolerant genotypes are determined by the Ideal Genotype Selection Index (SIIG).

In 2013, in an experimental farm in Karaj, 50 soybean genotypes were cultivated in two normal and drought stress conditions in a randomized complete block design with three replications. Irrigation cycle was determined based on the amount of evaporation from the surface of Class A pan. During the growth period, the reproductive period characteristics and after the ripening agronomic traits were evaluated. After collecting experimental data, analysis of variance, mean, minimum, maximum values of traits, heritability, phenotypic and genotypic variation coefficient, environmental variance, selection response, genetic gain, genetic and phenotypic variance, genetic and phenotypic correlation, and SIIG index method was used for grouping genotypes based on drought tolerance.

Among the the reproductive period characteristics the highest and lowest genetic gain in normal conditions were 21.40 and 3.95% for day to the beginning of seed filling and the Reproductive relative duration respectively and in stress conditions were 21.9 and 7.3% for day to the beginning of seed filling and the Reproductive relative duration respectively.In normal conditions, the highest genetic gain was 0.52 for the number of pods per plant and the number of branches and the lowest genetic genetic gain was 0.14 for the number of nodes per stem. In stress conditions, the highest and lowest genetic gain were 104% and 0.14 for the number of pods per plant and the number of nodes per stem, respectively. In normal conditions, among the agronomic traits, the highest values of response to indirect selection of grain yield were 1.6 and 1.41 g, through 100-grain weight and number of seeds per plant respectively and in stress conditions, the highest values of response to indirect selection of grain yield were 1.04, 0.89 and 0.87, through The number of branches, number of seeds per plant and weight of 100 seeds were obtained respectively. Also, according to the Ideal Genotype Selection Index (SIIG), five genotypes were in the tolerant group, seven genotypes in the semi-tolerant group, 11 genotypes in the semi-susceptible group and 27 genotypes in the susceptible group. Roanak, Kabalovskaja and TMS genotypes were identified as the most drought tolerant and AGS 363, Hermen and Kuban as the most drought sensitive genotypes.

Based on the results, acceptable phenotypic and genotypic diversity in terms of agronomic traits was observed among the studied genotypes. Most of the genetic parameters measured were almost identical under both normal and stress conditions. The characteristics of the reproductive period had higher e selection response (direct and indirect), higher broadsense heretability and higher genetic gain than the agronomic characteristics. The highest indirect to direct selection efficiency for grain yield were obtained from number of seeds per plant and 100-seed weight under normal conditions,and The highest indirect to direct selection efficiencies were obtained from number of sub-branches, number of seeds per plant and 100-seed weight in stress conditions. Also in this study, based on the ideal genotype selection index (SIIG), Roanak, Kabalovskaja and TMS genotypes were identified as the most tolerant and AGS 363, Hermen and Kuban as the most sensitive genotypes.