Genome‐Wide Association Mapping of Carbon Isotope and Oxygen Isotope Ratios in Diverse Soybean Genotypes

Water deficit stress is a major factor limiting soybean [ Glycine max (L.) Merr.] yield. High water use efficiency (WUE) offers a means to potentially ameliorate drought impact, but increased WUE is often associated with a reduction in transpiration ( T ) and an accompanied reduction in photosynthesis. This interdependence of T and photosynthesis is a major constraint in selection for high WUE by breeding programs. Measurement of genetic variability in WUE and T through carbon isotope ratio (δ 13 C) and oxygen isotope ratio (δ 18 O), respectively, could be important in identifying genotypes with high WUE that also have relatively high T , and thus higher rates of biomass production. This study's objective was to identify genomic regions associated with δ 13 C and δ 18 O. A diverse collection of 373 soybean genotypes was grown in four field environments, and whole‐plant samples collected at early reproductive growth were characterized for δ 13 C and δ 18 O. After quality assessment, 31,260 polymorphic single‐nucleotide polymorphism (SNP) markers with a minor allele frequency ≥5% were used for association analysis. Genome‐wide association analysis identified 54 environment‐specific SNPs associated with δ 13 C and 47 SNPs associated with δ 18 O. These SNP markers tagged 46 putative loci for δ 13 C and 21 putative loci for δ 18 O and may represent an important resource for pyramiding favorable alleles for drought tolerance and identifying genotypes with high WUE.