The evaluation of spermidine polyamine foliar spraying effects on improving some physiological indices and yield in soybean under low-irrigation condition

To evaluate of spermidine polyamine (SPD) foliar spraying effect on physiological indices and soybean yield (cv.'Caspian') under low-irrigation condition, a split-plot experiment was conducted based on randomized complete block design with three replications in Chapakrood, Joybar, Mazandaran province, in the year of 2016. The treatments incorporated the four levels of irrigation (100, 70, 50 and 30% of water requirement) as main plots and the three levels of foliar spraying SPD (0 (control), 0.5, 1 mM) as sub-plots. The evaluated parameters includes leaf number, pod number per plant, plant height, seed number per plant, the thousands seeds weights, the dry matter yield in a single plant, seed yield in a single plant, membrane stability index (MSI), relative water content (RWC), electrolyte leakage (EL), malondialdehyde (MDA), and hydrogen peroxide (H2O2). The results displayed that the application of SPD in various concentration had a significant effect on all characteristics except leaf numbers under low-irrigation conditions. In the evaluation of the interaction effects, the exhibited results showed that between low- irrigation and SPD, the SPD spraying concentration at the rate of 1 mM by reduced irrigation conditions from normal water requirement (100%) to its 30% requirement will result in significant incense in the pod number, seed number per plant, one thousands seeds weight, and dry matter yield by 90, 90, 50 and 20 %, respectively. Also, RWC and MSI increased up to 63% and 1.13 times, respectively, while EL decreased by 16% as compared to no-SPD conditions. With the decrease of irrigation rate to 30 % water requirement, the SPD concentration of 0.5 mM made seed yield to increase up to 90%, while H2O2 and MDA decreased to 67% and 34%, respectively that is the indication of plant drought tolerance. In sum, the results indicated the positive effect of the application of SPD improved drought tolerance in soybean (cv.'Caspian') under low-irrigation condition through the improvement of physiological characteristics and yield components.