The Role of Salicylic Acid in Improving the Photosynthetic System of Soybean (Glycin max L.) Genotypes under Drought Stress

To investigate the effect of salicylic acid on photosynthetic system and seed yield in soybean genotypes under drought stress a factorial experiment was conducted in a completely randomized design in both greenhouse and laboratory of Mohaghegh Ardebili University in 2015. The factors consisted of water stress at 3 levels (85, 65 and 45% of field capacity), salicylic acid at 3 concentrations (0, 0.4 and 0.8 mM) and three soybean genotypes, Williams, D42X19, and L17. The results showed that the relative water content, stomatal conductance, chlorophyll a and b, chlorophyll a/b ratio, leaf area, maximum fluorescence and quantum yield decreased as the result to drought stress, while Williams showed more tolerance to drought stress as compared to other two genotypes. Application of 0.4 mM salicylic acid as compared to high concentration (0.8 mM) and control was the most effective treatment on reducing the adverse effects of drought stress. It could be said that this may increase the relative water and chlorophylls contents, leaf area, quantum yield and stomatal conductance under drought stress conditions. It seems that carotenoid contents as a result of drought stress and application of 0.8 mM salicylic acid were increased in soybean genotypes, especially in L17. SLA was also increased due to drought stress, which was higher in L17 genotype than other genotypes. According to the results of this study, williams genotype was the most tolerant to drought stress as compared to the other genotypes, and the application of salicylic acid would enhance tolerance to drought stress in soybean genotypes.