Investigating the Genetic Control of Tiller Development in Barley.

Barley is the fourth most abundant crop worldwide in terms of production and acreage (faostat.fao.org). Barley grain is used for human food, animal feed, and malting and brewing. Barley shoot architecture is largely defined by the number and vigor of tillers, lateral shoots that arise from axillary meristems (AXM) at the plant base. The majority of grain yield in barley comes from tillers, but a more comprehensive understanding of the genetic basis of shoot architecture and potential trade-offs with other traits is necessary to improve shoot architecture of barley for grain yield. The aims of this study were (1) to characterize natural phenotypic variation for tiller number, tillering rate, and interactions between these and other important traits; (2) to identify quantitative trait loci (QTL) associated with tillering and other traits and potential genetic relationships between them; and (3) to identify gene expression patterns important for early tiller development. For the first two aims, 768 genetically diverse lines from the USDA National Small Grains Core Collection (NSGCC) were grown in the field in 2014 and 2015. Data was collected for tiller number from two weeks past-emergence to harvest, flowering time, and yield-related traits like grain size and number of grains per inflorescence. Mixed linear modeling and correlations between tillering and other traits indicate that tillering is pleiotropically influenced by other traits, primarily grain number and flowering time. This relationship was further demonstrated by extensive overlap of tillering QTL with grain number and flowering time QTL. Laser microdissection RNA-sequencing analysis revealed 372 genes differentially expressed between AXM and shoot apical meristem (SAM) tissues at two seedling stages that may influence early tiller development, several of which overlap tillering QTL. Results of this study will enhance our understanding of tillering and ability to fine-tune tiller number for crop improvement.