Investigating some biochemical and morpho-physiological reactions of soybean genotypes to drought stress in summer cultivation

Drought stress is the main factor in reducing production and the area under soybean cultivation. In order to investigate the effect of drought stress on the biochemical and morphophysiological characteristics of soybean [Glycine max (L.) Merrill], an experiment was conducted with 19 soybean genotypes in two environments without drought stress (watering weekly) and drought stress (watering every 10 days) in the form of a randomized complete block design with three replications in Khorramabad in the summer of 2017. The results of the analysis of variance showed that drought stress decreased the amount of chlorophylls a, b, a+b and a/b (66.6%, 37.2%, 53.8% and 43.9%, respectively); decreased the amount of phosphorus, potassium, iron and zinc in aerial parts (39.7, 69.8, 24.4 and 38.4 percent, respectively) and decreased the amount of phosphorus and zinc in seeds (0.10 and 7.2 percent, respectively), but it resulted in an increase in peroxidase and catalase of the shoot (0.15 and 47.6 percent, respectively) and an increase in the amount of potassium and iron in the seed (11.8 percent and 4.7 percent, respectively). Among the genotypes, the highest amount of aerial organ chlorophyll a was obtained from genotype number 1 and the lowest amount was obtained from genotype number 16. The comparison of the means by the cutting method showed that in the normal environment, the highest amount of aerial organ peroxidase was obtained from genotypes No. 8 and 9 and the lowest was obtained from genotype No. 19. While, in the stress environment, the highest amount of aerial organ peroxidase was obtained from genotypes number 6 and 15 and the lowest from genotype number 8. The trend of changes in grain yield and soybean leaf area index at different levels of the interaction effect of drought stress and genotype followed a significant and negative linear relationship, but the trend of changes in leaf temperature and shade floor light intensity followed a significant but positive linear relationship. In general, based on the amount of seed production, genotype number 7 is recommended for conditions without drought stress and genotype number 9 for drought stress conditions under moderate climatic conditions such as Khorramabad.