: The effect of salicylic acid on some agrophysiological and biochemical traits of soybean genotypes under drought stress conditions

In order to study the effect of using salicylic acid in inducing tolerance mechanisms to drought stress, a research was carried out in the field of Moghan Agriculture and Natural Resources Research Center in 2014 and 2015 as a split factorial in three replications. The main factor includes irrigation treatments based on evaporation from class A evaporation pan (100, 135 and 170 mm evaporation) and secondary treatments including soybean genotypes (Williams, L17 and D42X19) and salicylic acid foliar spraying (0, 0.4 and 0.8 mM). The results of composite analysis showed that drought stress significantly reduced plant height, number of nodes per stem, days to flowering and days to maturity in soybean genotypes. Seed yield was reduced by 38% in moderate stress and 46% in severe stress compared to control. Drought stress and application of salicylic acid, especially at a concentration of 0.4 mM, increased the concentration of amino acids such lysine and methionine. The highest amount of lysine was observed in Williams genotype under severe stress conditions and the highest amount of methionine was observed in D42XI9 genotype under moderate stress conditions. The highest level of activity of polyphenol oxidase enzymes in D42XI9 genotype and the highest level of glutathione reductase enzyme activity in Williams genotype was observed under severe drought stress conditions. Foliar spraying with salicylic acid (0.4 mM) increased the activity of these enzymes in both stressed and non- conditions. Intensity of stress caused an increase in concentration trihalose. But the effect of stress on the amount of trihalose in Williams genotype was more than other genotypes. With the application of salicylic acid, the concentration of trihalose increased in all genotypes, and the effective concentration of salicylic acid to increase trihalose was 0.8 mM. Drought stress and application of salicylic acid increased flavonoid accumulation in all genotypes and especially in L17 genotype. Drought stress significantly reduced plant height, number of nodes, days to flowering, days to maturity and seed yield in soybean genotypes, while the use of 0.4 mM salicylic acid improved the above traits, especially in the Williams genotype. In this study, Williams showed less sensitivity to drought stress (12% more seed yield than L17 genotype and 6% more than D42XI9 genotype) due to higher antioxidant enzyme activity and higher seed yield compared to other genotypes, and the use of salicylic acid in non-stressed and stressed conditions increased seed yield in soybean genotypes.