Association Mapping of Quantitative Trait Loci for Tillering Traits in Barley

The majority of grain yield in barley comes from inflorescences that develop on lateral stems called tillers. Despite the fundamental relationship between tiller production, or tillering, and yield, the underlying genetics are not well understood. In this study, the global genetic diversity of barley represented in the National Small Grains Core Collection (NSGCC) was exploited to maximize detection of quantitative trait loci (QTL) associated with tillering. Three hundred eighty-four spring, two-row lines and 384 spring, six-row lines were selected by including the most genetically diverse lines from the NSGCC. Lines were genotyped with 4500 SNP markers. Tillering traits were measured for each line, including average tillers per plant, measured weekly from two weeks until eight weeks past emergence; average productive tillers per plant; and average tiller mortality. Additional traits like heading date, plant height, and percentage of plants lodged were also measured. Extensive phenotypic variation was observed for all traits measured. As expected, two-row lines produced more tillers than six-row lines on average, but, despite this, one-quarter of all six-row lines produced more tillers than the two-row average. The week that tillering stopped was positively correlated with heading date as expected. Preliminary genome-wide association mapping was used to detect a QTL associated with tiller number that overlapped the Photoperiod-H1 locus, which controls heading date. Additional analyses to detect tillering QTL and traits correlated with tillering are ongoing and will result in a better understanding of tillering genetics, which could lead to improvement of yield and other agronomic traits in barley.