Effects of concentration and time of brassinosteroid treatment on growth and yield of soybean under drought stress conditions

Abstract

Soybean (Glycine max (L.) Merrill.) is an essential food and industrial crop, but it can be heavily affected by drought, especially during the pod growth stage. Brassinosteroids (BRs) are reported to alleviate drought stress, but the effectiveness may depend strongly on BR concentration and timing of the application, and no research has investigated this issue. This study aimed to determine the suitable concentration of BRs and time of treatment to help soybean plants withstand drought conditions during pod growth. The experiment was conducted with a completely randomized design, with four concentrations of BRs: 0 ppm (water) (B0), 0.1 ppm (B1), 0.2 ppm (B2), 0.3 ppm (B3), and three-time points for the application of BR treatment: soaking before sowing (T1), leaf spray when 50% of plants flowered (T2), leaf spray when 50% of the plants had pod at least 0.5 cm in length (T3). The results showed that when treated with different concentrations and treatment times of BRs, there was no difference in plant growth and development. However, there were differences in the yield of soybean plants. Specifically, treatment B2T2 had the highest total number of firm pods and the highest number of firm seeds at 22.2 and 44.6, respectively, with the weight of 100 seeds reaching 17.9 g, leading to the highest actual yield of 97.0 g/plot. These results indicate that with appropriate concentration and timing (0.2 ppm during flowering), the application of BRs can significantly alleviate drought stress effects on soybean plants during pod growth, improving seed yield and quality.