Carbon Isotype Discrimination and SNP Markers Association in Soybean Genotypes.

Water deficit stress continues to be one of the major factors limiting soybean yield [Glycine max (L.) Merr.]. Soybean genotypes with increased water use efficiency (WUE) may be used to develop cultivars with increased yield under drought.  Carbon isotope discrimination has been used as a simple and reliable measure for WUE in diverse crops with C3 photosynthesis.  The magnitude of carbon discrimination varies with photosynthetic type, environment, and genotype. A collection of 342 diverse soybean genotypes were grown in two years at two different sites and characterized for carbon isotope discrimination.  These genotypes were separated into two broad clusters and three distinct sub-clusters based on 31 SNP markers. Analyses of phenotypic data were conducted to examine the relationship between genetic clustering and phenotypic responses. Mean carbon isotope discrimination among the clusters were statistically compared and revealed that one sub-group was significantly different from the other two groups. Although the carbon isotope discrimination values were significantly different between the two locations in both years, results were consistent across years and locations. The results indicate that the 31 identified SNP markers can be used to interrogate diverse germplasm for CID and thus potentially identify CID as a selection tool to improve WUE in soybean for improved drought tolerance.