Genetic Variation and Trait Architecture for Nitrogen Use Efficiency in Elite Barley Germplasm

Rising CO₂ concentrations cause inhibited nitrate assimilation in plants, reducing their productivity and protein levels. Growing crop varieties with improved nitrogen use efficiency (NUE) could counteract this hindrance. We evaluated NUE-related traits in an association mapping (AM) panel consisting of 256 spring six-row barley (Hordeum vulgare) lines representing five breeding programs. The panel was genotyped with 3,072 SNP markers and was grown under a nitrogen-limiting and a non-limiting treatment in Crookston, MN in 2011 and 2012 and in Prospect, ND in 2012. The objectives of this study were to: 1) determine genetic variation for NUE in the AM panel and to 2) define the genetic architecture of NUE. Three traits (grain yield, grain protein, and total protein yield) and two NUE indices, namely geometric mean (GM) and stress tolerance index (STI), for these three traits consistently showed significant genetic variation in the panel. Using AM, we identified markers associated with grain protein and the GM and STI indices of grain protein at several regions on chromosome 6H with a Q+K model. Some of these markers map to a region previously associated with grain protein concentration referred to as GPC1. The markers identified five haplotypes, three of which have significantly different grain protein values, corresponding to low, medium, and high protein alleles that have been isolated in near isogenic lines. Genetic variation for NUE indices and markers linked to loci for these traits should inform breeding efforts to improve malting barley for NUE.