Genome-Wide Association Mapping of Nitrogen Use Efficiency Traits in Hard Winter Wheat

Improved nitrogen use efficiency (NUE) is important to the long-term sustainability of winter wheat production in the Great Plains of the United States. Nitrogen harvest index (NHI, grain N yield/total above-ground N) and nitrogen utilization efficiency (NUtE, grain yield/total above-ground N) were measured for 263 genotypes in grown near Ithaca, NE in 2012 and 2013. Genome-wide association scans (GWAS) with high density (20,010 SNPs) marker data were evaluated. Genotypic correlations of NHI and NUtE across the two trial years were limited (r = 0.36 and 0.37, respectively). Not surprisingly, the GWAS identified different regions of the genome regulating NHI and NUtE in the two trial years. In 2012, a season characterized by a warm, early Spring, NHI was associated with SNPs mapped to 1A, 2A, 3A, 4A, 6B, 7A, and 7B. In 2013, a season characterized by a cool, late Spring, NHI was associated with SNPs mapped to 1B, 2B, 4B, 6B, 7A, and 7B. In 2012, NUtE was associated with SNPs mapped to 2A, 3A, 4A, 4B, 6B, and 7B. In 2013, NUtE was associated with SNPs mapped to 1A, 1D, 2A, 2B, 2D, 3D, 4B, and 7B. Generally, effects of 4B predominated in 2013. Averaged across genotypes, grain yield was 29% greater in 2013 than in 2012. The Rht-B1b dwarfing gene may be associated with the observed effects of 4B SNPs on NUE traits in the higher-yielding 2013 environment. Genomic regions identified in these trials will be compared to previous reports.