Identification of Putative Genomic Loci for Total Chlorophyll in Soybean Using Leaf Extracts and High Throughput Spectral Reflectance Approaches.

Photosynthetic capacity is important for total biomass production and ultimately grain yield. The amount of solar radiation that is absorbed by a leaf is closely related to its chlorophyll concentration, which generally is positively related with photosynthetic rate. A better understanding of the genetic basis of chlorophyll concentration in soybean [Glycine max (L.) Merr.] may eventually be leveraged to improve photosynthetic capacity and increase seed yields. A collection of 332 diverse soybean genotypes were grown in two years (2009 and 2010) and total chlorophyll content (eChl_T) was determined spectrophotometrically based on leaf disc extracts. In addition, canopy chlorophyll content was determined based on canopy spectral reflectance characteristics using two methods. Chlorophyll contents were determined using i) an equation based on wavelet transformed spectral reflectance (tChl_T) and ii) a spectral reflectance index (iChl_T). A genome-wide associating mapping approach was employed using 31,253 single nucleotide polymorphisms (SNPs) to identity SNPs associated with these three methods (eChl_T, tChl_T, and iChl_T) of chlorophyll content determination. A total of 52 unique SNPs showed a significant association with total chlorophyll content in at least one of the three approaches (eChl_T, tChl_T and iChl_T) and likely tagged 27 putative loci for total chlorophyll content.  Among the 27 putative loci identified, four loci were revealed by all three approaches.  This study demonstrates that putative loci for chlorophyll content can be identified in soybean using extract as well as canopy spectral reflectance based methods.  In addition, these results demonstrate the potential to employ rapid, non-destructive canopy spectral reflectance-based phenotypes for genetic mapping.