Association Mapping of Yield Components in 2-Row Spring Barley from the USDA National Small Grains Collection.

Barley, Hordeum vulgare L., ranks 4^th in the world for cereal grain production and is an important crop for animal feed, malt and human consumption. Barley is a diploid species that is especially well adapted to poor soil conditions and drought. The USDA National Small Grains Collection (NSGC) contains over 33,000 barley accessions. Previously, a core subset of 2,417 accessions representing the diversity in the NSGC was genotyped with the Illumina 9K barley SNP chip. Association mapping with this material found strong QTL for hull cover, spike row number and heading date (Munoz-Amatriain et. al., 2014). From this subset we chose 480 2-row spring barley accessions and measured yield components including test weight, protein content, thousand kernel weight, and kernel width, length, volume and diameter in terminal drought and low nitrogen environments. The distribution of these traits across these 480 spring accessions and landraces with exceptional trait characteristics are identified and discussed in the present study. QTL and linked SNPs will also be discussed for the yield component traits that span all seven barley chromosomes.