Evaluation of genetic variation and relationships of agronomic traits in soybean genotypes under normal irrigation and water deficit stress

The soybean (Glycine max L.) is one of the most important source of grain oil and protein in the world. It contains 18 to 22% oil and 40 to 50% good quality protein. The low productivity of the pulses especially soybean may be attributed to their susceptibility to pathogenic microorganisms, biotic and abiotic stresses. Soybean production is expected to increase significantly in the world. However, the yield of soybean is still low. The cultivation of soybean in arid and semi-arid areas which face drought and are poor in soil nutrients is one of the main reasons for the low yield of soybean. Evaluation of genetic diversity and identifying genotypes with high yielding potential and tolerant to the environment stresses could be valuable for progressing in future breeding programs.
In order to evaluate of genetic diversity and tolerance to water deficit stress, 40 soybean genotypes were selected from maturity group III and IV and evaluated in a randomized completely block design (RCBD) under both normal and water deficit conditions, in 2015 on the research field of Seed and Plant Improvement Institute-Karaj, with three replications. Agronomic characteristics were including days to flowering (R1), days to poding (R3), days to beginning of seed forming (R5), days to end of seed filling (R6), seed filling duration (R5-R6), days to beginning of maturity (R7), reproductive stage duration (R1-R7), days to maturity (R8), hundred-seed weight, number of seeds per plant, number of pods per plan, number of pods in sub branches, number of sub branches, plant height, relative water content, oil content, protein and grain yield. After normality test of errors distributions, test of equality of variances and test of the additive effects of treatment and block, data were statistically analyzed using GLM procedure with SAS 9.4. Principal component analysis and drawing of biplots were performed using SPSS 21 and Statgraphics 16, respectively.
Under both normal irrigation and water deficit condition grain yield, number of seeds per plant and number of sub-branches showed not only higher phenotypic and genotypic coefficient of variation, but also illustrated higher heritability and genetic advance. Grain yield (43.24%), plant height (29.84%), number of seeds per plant (23.53% ), seed filling duration (22.06%) and number of pods per plant (21.69%) showed higher reduction in water deficit stress, respectively, while oil content increased under water deficit stress conditions (11.96%). Days to flowering, number of sub branches, days to poding and days to beginning of seed forming had the least reduction with 0.66, 1.28, 2.83 and 3.81 percent, respectively. The GN-2171, GN-2156, Spry×Savoy/2 and GN-2152 genotypes showed higher grain yield reduction with 88, 74, 66 and 61 percent, respectively while GN-2125, GN-2165 and GN-2002 had lower grain yield reduction with about 10 to 11 percent. Although GN-2125, GN-2165 and GN-2002 genotypes showed lower yield reduction under water deficit stress condition, they did not have higher grain yield under both normal irrigation and water deficit stress conditions. Not only the D42.I4, Spry×Savoy/3, D42.I9 and DI-74 genotypes under both normal irrigated and water deficit conditions had higher grain yield but also they showed lower grain yield under water deficit stress. Corresponding biplot graph, the L6-P79, Chaleston×Mostang/12, D42×Will82, Spry×Savoy/3 and DI-74 genotypes revealed higher values of the factors of grain yield and its components which they could be consider the genotypes with high grain yield in both normal irrigation and water deficit condition.
Although, the D42×Will82 and Chaleston×Mostang/12 genotypes had high grain yield in both condition but they showed high reduction in water deficit stress condition. So, they are suitable to be cultivated in both normal irrigation and water deficit stress even though they are relatively sensitive to water deficit stress condition.