Genetic exploration of spike and seed morphology in a two-rowed barley nested association mapping panel

Abstract

Barley (Hordeum vulgare) is unique as it has six-rowed cultivars and two-rowed cultivars. The six-rowed has three fertile florets on each spikelet, while two-rowed has only a single fertile center floret per spikelet. This by itself affects seed uniformity as seed produced in the lateral florets tend to be less symmetrical and smaller in size than the center floret. Yield and plumpness are also affected by spike morphology. While the genes and alleles affecting six-rowed vs. two-rowed spikes are known, there are a number of other genes that affect additional spike morphological traits such as number of seeds per head, length of head, and compaction of spikelets. Here, a two-rowed Nested Association Mapping (NAM) population was used to genetically dissect barley spike and seed morphology. To create the population, 13 diverse founder lines of barley were crossed with Conlon, a high yielding, plump, spring variety. Approximately 80 progenies were selected from each of the Conlon by founder crosses, and then backcrossed to Conlon in hopes of exposing the advantageous traits while adapting lines to the Great Plains of the Northwest. The population varying for spike and seed morphology was grown out in a field trial in Bozeman, MT and Logan, UT where phenotypic data was collected throughout the stages of growth and harvest. At maturity (Zadok's 50) stage five heads from each of the lines were collected. Digital Image Analysis was used to measure spike length, kernel count, density, and seed size. Genetic maps were created for each family as well as a consensus map for the whole population. Associations between the phenotypic data and the genotypic data observed in the individual families and consensus map allowed us to identify QTLs conserved across multiple families as well as unique to individual families. Evidence of pleiotropic effects between traits was observed. Some of the QTLs previously were identified, and some are novel. One of the families was of particular interest due to unique QTLs impacting seeds per spike and seed weight. Additionally, several novel QTLs were identified on chromosome 7H that highly impact seed traits.