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 (δ13C) and oxygen isotope ratio (δ18O), 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 δ13C and δ18O. 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 δ13C and δ18O. 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 δ13C and 47 SNPs associated with δ18O. These SNP markers tagged 46 putative loci for δ13C and 21 putative loci for δ18O and may represent an important resource for pyramiding favorable alleles for drought tolerance and identifying genotypes with high WUE.