Phenotypic, Spectral Reflectance, and Genetic Analysis of Yield in Spring Wheat Accessions

The USDA’s National Small Grains Collection (NSGC) contains over 42,000 genetically diverse wheat (Triticum aestivum) accessions of diverse geographic origin.  A total of 540 spring wheat NSGC accessions were evaluated under irrigated and water stressed environments over two years.  Grain yields were assessed by canopy spectral reflectance (CSR) and loci for high grain yield were identified through a genome-wide association study (GWAS). The effects of drought on yield for each accession was assessed through the drought susceptibility index (DSI).  Phenotypic analysis of grain yields and DSI found landrace accessions had yields and levels of drought tolerance similar to cultivars and breeding lines.  Grain yields and DSI across both years of the study identified 39 high yielding drought tolerant accessions, of which, 10 were landraces.  CSR indices explained up to 46% of the yield variation and identified over 80% of the highest yielding accessions.  Selection by CSR gave a 20% increase in grain yield when compared to randomly selected accessions.  GWAS identified six loci significantly associated with yields on chromosomes 4A, 5B and 6A, as well as a single locus on chromosome 2B associated with yields in both irrigated and terminal drought environments in each year.  Markers identified on 6A gave 9% to 19% increases in yield and selection using the 2B locus gave 7% to 15% increase in yield.  The genetic loci identified in this study may be of value for MAS and the landrace accessions identified here are good candidates for incorporation of genetic variation into current breeding programs.