Quantifying the physiological, yield, and quality plasticity of Southern USA soybeans under heat stress

Climate change is causing an increase in air temperature during the reproductive and grain-filling stages, which is detrimental to soybean production and quality. Assessing the variability induced by heat stress in morphophysiological, yield, and quality traits is an effective strategy for identifying heat-tolerant cultivars. In this study, ten soybean cultivars were exposed to temperatures 4.6 & DEG;C above the optimum (32 & DEG;C) from the R1 to R6 stages to investigate the heat stress-induced variability in morpho-physiological, yield, and quality traits. On average, stomatal conductance decreased by 11% under heat stress compared to the control. However, the cultivar R01-416F had the maximum increase in stomatal conductance (34%), and the least increase in canopy temperature ( + 2 & DEG;C) under the heat stress as compared to the control. Heat-stressed plants recorded a 3% reduction in chlorophyll content, with the cultivar DM45X61 experiencing the greatest decline of 22%. Across cultivars, specific leaf area decreased by 17% under heat stress, with G4620RX recording the highest reduction (28%). The results revealed a significant reduction in pod number (3.8%), pod weight (4%), seed number (4.2%), seed weight (5%), and hundred-seed weight (1.1%) per & DEG;C increase in temperature over the control. However, among the ten cultivars, R15-2422 and LS5009XS displayed relatively less reduction in seed number under heat stress. In comparison to the control, the cultivar R01-416F had the highest reduction in seed protein (4.4%) under heat stress, while it recorded a 16.6% increase in oil. Based on the phenotypic plasticity index, the cultivars R15-2422, and LS5009XS demonstrated the potential of maintaining higher yields under hot conditions. These findings highlight the significant impact of heat stress on soybean plasticity. The knowledge generated in this study helps in selecting and developing cultivars that can withstand heat stress, thus maintaining productivity and quality in warmer climates.