Introduction: Soybean (Glycine max L.) is the most important oil crop in the world. Soybean yield and its geographical distribution in the country can be severely limited by abiotic stress such as drought. There is a constant need to improve soybean cultivars with stable yields in different environments. The main goal of the mostly soybean breeding programs is the selection of desirable genotypes with high yield and stability. Genotype × environment interactions for quantitative traits such as grain yield cause genotypes to have different relative yields in different environments. In many statistical methods that have been used to determine yield stability and adaptability of cultivars, some basic assumptions of stability analysis, such as the nonlinear response of genotype and environment and dependence of environmental index on the mean of genotypes, are not true.
The soybean genotype's stability and high performance are essential factors for long-term development and food security. That the occurrence of various stresses, including drought stress, can cause high losses in the production and supply of this product. This factor has caused the wide attention of researchers to evaluate the stable and tolerant genotypes to drought stress in different environments to introduce the best variety. For grain yield stability analysis, genotype by environment interactions are crucial in properly identifying and discriminating between varieties.
Materials and Methods: To investigate the effect of drought stress on the stability of soybean yield, an experiment with 19 soybean genotypes was conducted in two environments without stress (weekly irrigation) and drought stress (biweekly irrigation) in a randomized complete block design with three replications in two consecutive years in Khorramabad.
Results and Discussion: The results of the combined analysis of variance of grain yield in two experiments in two years showed that grain yield was significantly affected by the simple and interaction effects of year and genotype (p<0.01). The percentage contribution of the variance of environment, genotype, and genotype-environment interaction was 58.3, 20.7, and 16.04%, respectively, and for this reason, the stability of the grain yield of the genotypes was evaluated through two graphical methods, AMMI and GGE-biplot. The results of the comparison of the means showed that the highest grain yield was obtained in non-stress conditions in genotypes G2, G3, G4, and G13, and in drought stress conditions in genotypes G5, G9, G11, and G13. According to the biplot diagram of the two principal components, IPC1 and IPC2 in the AMMI analysis method, the genotypes G2, G3, G4, and G16 were distributed in the center of the biplot, in addition to high yield, and had general stability in all environments. In this method, the genotypes with specific stability to non-stressed and stressed environments were also identified. In the GGE-Biplot method using a polygonal diagram display, genotypes 9G, 11G, and 13G had specific stability to the stress environment, and genotypes G2, G3, and G4 were compatible with the natural environment. Also, to simultaneously select the branch yield and stability of the genotypes, the display of the average environmental coordinate (AEC) line that passes through the coordinate axis was used, and genotypes G2, G3, G4, and G13, which were located near the ATC line, in addition to having high yield, had stable performance in all environments.
Conclusion: The soybean genotypes' stability and high performance are essential factors for long-term development and food security. Therefore, based on both methods, genotypes 2G, 3G, 4G, and 13G were identified as high-yielding and stable genotypes in both stress-free and drought stress conditions. Among them, genotype G13 in drought stress conditions and genotype G7 with special stability in normal irrigation are recommended for subtropical climates such as Khorramabad and can be used in future breeding programs.