HIGH DAY TEMPERATURES DURING SEED-FILL ARE NEGATIVELY IMPACTING SOYBEAN YIELD AND GRAIN QUALITY. CLIMATE MODELS PROJECT THAT US SOYBEAN GROWING REGIONS WILL NOT ONLY EXPERIENCE INCREASED MEAN SEASONAL HIGH TEMPERATURES, BUT ALSO FREQUENT EPISODES OF HIGH DAY TEMPERATURE STRESS. THE ADVERSE EFFECTS OF HEAT STRESS CAN BE MITIGATED BY DEVELOPING SOYBEAN CULTIVARS WITH IMPROVED HEAT STRESS TOLERANCE. THEREFORE, WE PROPOSE TO: (1) PHENOTYPE A GENETICALLY DIVERSE SOYBEAN ASSOCIATION PANEL FOR POST-FLOWERING HEAT STRESS INDUCED YIELD AND COMPOSITION CHANGES, (2) MAP GENOMIC REGIONS RESPONSIBLE FOR SUSTAINING YIELD, QUALITY AND COMPOSITION UNDER POST-FLOWERING HEAT STRESS THROUGH GENOME WIDE ASSOCIATION STUDIES, AND (3) VALIDATE HAPLOTYPES AND DEVELOP KOMPETITIVE ALLELE SPECIFIC PCR (KASP) ASSAYS WITH THE GOAL OF STRENGTHENING BREEDING EFFORTS TO IMPROVE SOYBEAN RESILIENCE UNDER POST-FLOWERING HEAT STRESS IN THE FUTURE. A UNIQUE FIELD-BASED HEAT TENT FACILITY WILL BE USED TO QUANTIFY THE HEAT STRESS INDUCED PHENOTYPIC VARIABILITY FOR SEED YIELD AND SEED COMPOSITION IN 300 SEQUENCED GERMPLASM ACCESSIONS OVER TWO CONSECUTIVE SEASONS. HAPLOTYPES WITH CONTRASTING RESPONSES WILL BE VALIDATED UNDER FIELD BASED TENTS TO STRENGTHEN THE RATIONALE FOR USING STABLE AND CONSISTENT KASP ASSAYS. GENETIC REGIONS WILL BE MAPPED FOR TRAIT PLASTICITY INDUCING POST-FLOWERING HEAT STRESS TOLERANCE, AND THE DEVELOPMENT OF KASP ASSAYS WILL BEGIN FOR OPTIMIZING PHENOTYPES UNDER HEAT STRESS CONDITIONS. DISCOVERY OF KEY GENES AND PRECISE MOLECULAR MARKERS WILL HELP DEVELOP IMPROVED HEAT TOLERANT GERMPLASM, THROUGH GENOME ASSISTED BREEDING STRATEGIES. THIS PROJECT TEAM WILL MENTOR THE UNDERGRADUATE STUDENTS AND POST-DOCTORAL FELLOW ON THIS PROJECT TO PURSUE CAREERS IN PLANT RESEARCH.