Moringa leaf extract seed priming enhances antioxidant defense and soybean productivity under subtropical heat stress

Climate-induced heat stress disrupts soybean production by inducing excessive accumulation of reactive oxygen species (ROS). This is the first study evaluated whether seed priming with natural organic substances (Moringa leaf extract [MLE] 3%, guava fruit juice 2%, lemon juice 3%) induces thermotolerance more effectively than synthetic agents (KCl 0.05%, iron 0.05%) or hydro-priming under subtropical heat stress. A split-plot randomized complete block design with three replications was used, where two sowing dates (15 August, 1 September) were main plots and seven seed priming treatments (including an untreated control) were subplots. Data were collected on stand establishment, antioxidant enzyme activities, chlorophyll and oil content, and yield components. Sowing date showed no significant effect (p > 0.05). Priming treatments significantly affected all measured parameters (p < 0.05). MLE 3% produced the highest seed yield (1.6 vs. 0.85 t ha−1), germination (85.2 vs. 73.9%), and antioxidant enzyme activities, particularly SOD (+ 19.3%), CAT (+ 8.5%), and APX (+ 13.8%), compared with the control. Guava juice 2% was the second-most effective treatment. Priming with 3% MLE provided the most consistent benefits across all measured traits, suggesting its potential as an economically feasible strategy for improving soybean productivity under heat stress. This is among the first field studies comparing multiple natural and synthetic seed-priming agents under subtropical heat stress. This approach offers a promising, context-dependent strategy that warrants further validation through multi-location, multi-season trials before widespread recommendation for heat-prone subtropical soybean production.