Effectiveness of Soil, Foliar, and Seed Selenium Applications in Modulating Physio-Biochemical, and Yield Responses to Drought Stress in Vegetable Soybean (Glycine max L. Merrill)

Drought stress severely affects the physio-biochemical processes and yield of nutritious crops like vegetable soybean (<i>Glycine max</i> L. Merrill), threatening global food security and emphasising the need for effective strategies to improve drought tolerance. This study, conducted under controlled conditions in a greenhouse, investigates the effects of three selenium application methods (seed priming, foliar spray, and soil application) on photosynthesis efficiency, relative water content (RWC), hydrogen peroxide (H₂O₂), antioxidative responses, and yield traits of two vegetable soybean cultivars, UVE14 (drought-tolerant) and UVE17 (drought-susceptible), under drought stress. Among the three Se application methods, soil application was the most effective in improving drought tolerance and yield performance in both cultivars. In UVE17 (drought-susceptible), soil application significantly increased the number of seeds per plant (SPP) and the number of pods per plant (PPP), while in UVE14 (drought-tolerant) SPP increased. Selenium foliar spray and seed priming treatments did not increase yield in drought-stressed UVE14, suggesting that they are unlikely to further enhance tolerance in drought-tolerant cultivars. For UVE17 under drought conditions, selenium soil application improved key physio-biochemical indicators of drought tolerance, including photosynthesis efficiency (total performance of photosystems I and II, total chlorophyll content, and stomatal conductance), water retention (RWC), and carotenoid content. These improved physio-biochemical responses directly impacted yield outcomes. Notably, RWC and total chlorophyll content at the pod-filling stage in drought-stressed UVE17 were positively correlated with an increase in PPP under selenium soil application. Selenium soil application stands out as the most effective method for enhancing drought tolerance in vegetable soybean, presenting a promising and practical solution for enhanced crop production under climate change.