Genetic and genomic studies towards breeding for the utilization of Texas wintergrass (Nasella leucotricha) as a cool season forage grass

Texas wintergrass (Nassella leucotricha) presents a promising forage option for winter grazing, yet its commercialization is hindered by physiological dormancy, seed morphology constraints, and limited genetic diversity. This study addressed these challenges through seed dormancy analysis, genome assembly, and genetic diversity assessment. Dormancy was found to be primarily exogenous, with phenolic inhibitors and structural barriers restricting germination. Treatments with sulfuric acid scarification and hydrogen peroxide effectively improved germination, modulating abscisic acid (ABA) metabolic pathways. To facilitate molecular breeding, the first-ever genome assembly of Texas wintergrass was generated using Illumina and PacBio sequencing. The PacBio-derived genome exhibited improved resolution but limited alignment to the rice reference genome, underscoring its evolutionary divergence. Genome annotation identified key genes, transposable elements, and species-specific simple sequence repeats (SSRs), laying the foundation for marker-assisted selection. Transposable element analysis suggested that long terminal repeats (LTRs) may have contributed significantly to genome expansion, but highlighted the necessity for further genome refinement through chromosome-level sequencing. Genetic diversity analysis using SSR markers revealed low heterozygosity and a strong tendency toward self-fertilization across populations. Outcrossing was hypothesized to be strongest under wetter conditions, but populations from environments of this sort actually demonstrated low within population diversity. Phylogenetic clustering suggested that genetic similarity correlated with geographic proximity, though long-distance gene flow, likely driven by anthropogenic activity, still had some influence on population structure. These findings highlight the need for advanced breeding strategies, such as mutation breeding and genomic selection, to enhance genetic variation and improve agronomic traits in Texas wintergrass. Further genomic refinement and broader diversity assessments will support the development of Texas wintergrass as a commercially viable forage crop, optimizing its potential for sustainable livestock production.