Effect of plant growth regulators and drought duration on physiology, growth and yield of soybeans (Glycine max (L.) Merrill) at the pod growth stage

During the pod growth stage, soybeans (Glycine max (L.) Merrill) are very susceptible to drought. The research was carried out to investigate the extent of damages by different durations of drought on soybean plants during pod growth, and the capabilities of different plant growth regulators (PGRs) to mitigate these damages. The two-factor experiment was conducted in a completely randomized design, including 12 treatments with 3 replications. Factor A was the drought durations: 0 days (D0), 4 days without irrigation (D4), 8 days without irrigation (D8); and factor R was the PGR treatments: water (W), salicylic acid (SA), brassinolide (BR), and gibberellic acid GA3 (GA). Results showed that no differences in plant growth and development due to drought durations or PGRs were observed. However, longer drought durations severely reduced the yield by about 83.8% compared with control. Among the three PGRs used, brassinolide was most effective in mitigating drought stress effects on soybean plants, improving the total number of firm pods (35.0 pods), firm seeds (70.8 seeds), the weight of 100 seeds (16.6 g), and productivity (195.9 g). However, spraying brassinolide did not affect the protein, proline, and pigment contents.