Association Mapping of Total Leaf Carotenoids Based on Three Measurement Approaches in Diverse [Glycine max (L.) Merr.] Soybean Genotypes

Carotenoid biosynthesis occurs mostly in chromoplasts and chloroplasts, and its biosynthetic pathway is highly conserved in plants. Leaf carotenoids play an important photo-protective role during the process of photosynthesis and targeted selection of leaf carotenoids may offer avenues for improved abiotic stress tolerance. A collection of 332 genotypes was grown in 2009 and 2010 and total leaf carotenoid content (μg cm⁻²) was measured in all accessions using three different determination methods.  The first method was the determination of extractable carotenoid content (eC) in leaf tissue disks by wet chemistry whereas carotenoid contents were derived from spectral reflectance with an in-house algorithm (mC) and a published spectral reflectance index (iC).  An association mapping approach was employed using 31,253 single nucleotide polymorphisms (SNPs) to identity SNPs associated with total leaf carotenoid contents as indicated by the three measures. A total of 57 SNPs showed a significant association with total leaf carotenoid content based on at least one of the three measurement approaches. These 57 SNPs likely tagged 14 putative loci and demonstrated that markers for total leaf carotenoids can be identified in soybean based on wet chemistry derived carotenoid content as well as by spectral reflectance based measures.