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 morpho-physiological, 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 °C above the optimum (32 °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 °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 °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

Table_1_Impact of ultraviolet-B radiation on early-season morpho-physiological traits of indica and japonica rice genotypes.docx

Ultraviolet (UV)-B radiation is considered one of the major detrimental rays coming from the Sun. UV-B radiation has a harmful impact on plant growth and development. The effect of UV-B radiation was studied on 64 rice (Oryza sativa L.) genotypes during the vegetative season. An equal number of genotypes from the japonica (50%) and indica (50%) subspecies were phenotyped using the Soil-Plant-Atmosphere-Research (SPAR) units. The 10 kJ UV-B was imposed 12 days after planting (DAP) and continued for three weeks (21 d). Based on the combined ultraviolet-B radiation response index (CUVBRI) for each genotype, the 64 rice genotypes were classified into sensitive, moderately sensitive, moderately tolerant, and tolerant. Various shoot traits, such as plant height, tiller, and leaf numbers, were measured. We also studied critical root phenological traits like root volume, diameter, tips, and forks. Out of all the studied shoot traits, leaf area showed maximum reduction for both indica (54%) and japonica (48%). Among the root traits, root length decreased by negligible (1%) for indica as compared to japonica (5%), while root crossing and forks showed a maximum decline for japonica (37 and 42%), respectively. This study is timely, meaningful, and required because it will help breeders select a tolerant or sensitive rice line for better yield and production under abiotic stresses.</p

Table_2_Impact of ultraviolet-B radiation on early-season morpho-physiological traits of indica and japonica rice genotypes.docx

Ultraviolet (UV)-B radiation is considered one of the major detrimental rays coming from the Sun. UV-B radiation has a harmful impact on plant growth and development. The effect of UV-B radiation was studied on 64 rice (Oryza sativa L.) genotypes during the vegetative season. An equal number of genotypes from the japonica (50%) and indica (50%) subspecies were phenotyped using the Soil-Plant-Atmosphere-Research (SPAR) units. The 10 kJ UV-B was imposed 12 days after planting (DAP) and continued for three weeks (21 d). Based on the combined ultraviolet-B radiation response index (CUVBRI) for each genotype, the 64 rice genotypes were classified into sensitive, moderately sensitive, moderately tolerant, and tolerant. Various shoot traits, such as plant height, tiller, and leaf numbers, were measured. We also studied critical root phenological traits like root volume, diameter, tips, and forks. Out of all the studied shoot traits, leaf area showed maximum reduction for both indica (54%) and japonica (48%). Among the root traits, root length decreased by negligible (1%) for indica as compared to japonica (5%), while root crossing and forks showed a maximum decline for japonica (37 and 42%), respectively. This study is timely, meaningful, and required because it will help breeders select a tolerant or sensitive rice line for better yield and production under abiotic stresses.</p