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Abstract
Drought stress is the most important abiotic constraint affecting soybean [Glycine max (L.) Merr.] yield in rain-fed production areas. Combating this stress requires soybean plants which possess physiological mechanisms to tolerate episodic drought stress, because less than 10% of U.S. soybean production areas are irrigated. Evaluation of physiological traits that relate to drought tolerance can be used in breeding programs to identify genomic regions associated with the traits and genotypes with favorable combinations of alleles. The objective of this research was to evaluate drought tolerance related traits in two populations in order to identify germplasm and genetic loci to improve soybean drought tolerance. A panel of over 200 genetically diverse soybean accessions genotyped with the SoySNP50K iSelect BeadChips was phenotyped for canopy wilting, carbon isotope composition (13C), nitrogen concentration, nitrogen isotope composition (15N), and transpiration response to AgNO3. Additionally, 130 recombinant inbred lines (RILs) derived from Hutcheson PI 471938 genotyped with the SoySNP6K iSelect BeadChips were evaluated for canopy wilting. Genome-wide association analyses and composite interval mapping revealed genomic regions controlling these drought related traits in soybean, and new soybean accessions were identified with high numbers of beneficial alleles and favorable breeding values for the traits. The germplasm and genomic regions identified through this research can be used to better understand the genetic architecture for these traits and be incorporated into elite germplasm to improve drought tolerance in soybean.