Mapping Quantitative Trait Loci Controlling Seed and Grain Production Traits of Intermediate Wheatgrass (Thinopyrum intermedium).

Intermediate wheatgrass (Thinopyrum intermedium) is a cool-season perennial grass cultivated for seed used in forage production, conservation plantings, and consumable grain products such as flour. Intermediate wheatgrass (2n=6x=42) has a large, allohexploid genome (~13 GB) and is a distant relative of barley (Hordeum vulgare) and bread wheat (Triticium aestivum), which have similar range of adaptation.  However, wheat and barley produce substantially larger seeds that contain substantially more carbohydrate and produce more vigorous seedlings. Thus, improvement of seed size and other seed production traits is important for development of forage and grain varieties of intermediate wheatgrass. The development of next-generations technologies that enable low-cost genotype-by-sequencing (GBS) has created new opportunities to identify genes and single-nucleotide polymorphism (SNP) markers associated with key agronomic traits in any species, including semi-wild plants such as intermediate wheatgrass. In this project, a linkage map of 1,628 SNP markers in 21 linkage groups was developed from a full-sib family of 234 genotypes derived from a cross of two wheatgrass clones M26 and M35, including one free-threshing genotype. Sequences of SNP markers in these 21 linkage groups were aligned to the seven chromosome sequences of diploid barley (Hordeum vulgare) to identify three sets of seven sets of homologous chromosomes of allohexaploid intermediate wheatgrass. Seed mass, seed length, seed width, percent naked seed (free-threshing seed), seed shattering, number of spiklets per spike, and spike length were measured in clonally replicated field evaluations of the M26 x M35 family in Utah and Kansas. Progeny genotypes showed heritable variation with at least two-fold range of mean values. Comparisons of the number and location of these QTLs indicate that these are complex traits controlled by multiple independent genes. These results elucidate genetic architecture and demonstrate opportunities for genetic improvement of seed mass and other seed production traits in selected intermediate wheatgrass germplasm.