Identification of new germplasm sources and physiological traits for breeding heat-tolerant soybean varieties

Authors: HAMMOND, SHELBY - Clemson University; SATHASIVAM, MALARVIZHI - Clemson University; Fallen, Benjamin; Smith, James; BRIDGES, WILLIAM - Clemson University; RUSTGI, SACHIN - Clemson University; NARAYANAN, SRUTHI - Clemson University

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2025
Publication Date: 12/17/2025
Citation: Hammond, S., Sathasivam, M., Fallen, B.D., Smith, J.R., Bridges, W., Rustgi, S., Narayanan, S. 2025. Identification of new germplasm sources and physiological traits for breeding heat-tolerant soybean varieties. Crop Science. http://dx.doi.org/10.1002/csc2.70209.
DOI: https://doi.org/10.1002/csc2.70209

Interpretive Summary: High temperatures during the growing season are a serious threat to soybean production, especially when heat occurs during flowering and seed development. However, breeding heat-tolerant soybean varieties has been limited by a small pool of heat-tolerant genes and a lack of clear traits that breeders can easily select for in the field. To help address this challenge, research was conducted on nearly 200 soybean lines that were developed from a cross between a heat-tolerant parent and a heat-sensitive parent, with the goal of identifying lines that perform well under heat stress and determining which traits are most useful for selection. The study was carried out over two years in Pendleton, South Carolina. Plants were grown under normal conditions until flowering, after which they were exposed to high temperatures using special tents that created daytime heat stress of over 100°F for several hours per day for 14 days. Several soybean lines were identified as the most heat-tolerant based on leaf health, pollen viability, and seed production. It was found that seed yield under heat stress was closely linked to chlorophyll levels, photosynthesis, and biomass, with aboveground biomass showing the strongest heritability, making it a valuable trait for selecting heat tolerance in future breeding work. Through this research, new sources of heat-tolerant soybean germplasm were identified, and key traits that can help breeders more efficiently select for heat tolerance were established. These findings provide important tools for improving soybean productivity under stressful growing conditions, helping to ensure stable yields when crops are exposed to high temperatures.

Technical Abstract: Breeding for heat tolerance in soybean is constrained by limited genetic resources, lack of efficient selection criteria, and incomplete knowledge of heat tolerance mechanisms. The objectives of this study were to characterize the heat tolerance of a soybean recombinant inbred line (RIL) population based on traits defining leaf function, pollen viability and yield, and identify genotypes and traits that can be included in breeding programs for heat tolerance. Field trials were conducted at Pendleton, SC in 2022 and 2023 to test the heat stress responses of 192 RILs [derived from DS 25-1 (heat tolerant) x DT97-4290 (heat-susceptible)], parental lines, and 12 check varieties. Plants were grown at ambient temperatures until the onset of flowering; thereafter, a heat stress treatment (38-42°C at least for 4 hrs during the daytime) was established for 14 days using heat tents. The RILs 22, 26, 38, 54, 79, and 116 were identified as the most heat-tolerant and the RILs 177, 185, and 195 as the most heat-sensitive based on leaf physiology (chlorophyll index, chlorophyll fluorescence, lipid peroxidation, and photosynthesis), pollen viability, and yield (aboveground biomass, seed yield, and hundred seed weight). Seed yield was correlated with chlorophyll index, photosynthesis, and aboveground biomass under heat stress. Aboveground biomass was associated with the highest heritability (H2 = 0.48), reinforcing its significance as a key selection criterion for heat tolerance in soybean. The new germplasm sources for heat-tolerant variety development and the traits identified for improving the selection efficiency provide valuable resources to soybean improvement programs.