Exogenous control of dormancy and chemical regulation of germination in Texas wintergrass (Nassella leucotricha (Trin. & Rupr.) Pohl) seeds
Texas wintergrass (Nassella leucotricha (Trin. & Rupr.) Pohl) has potential as a cool-season forage but has not been used for such purpose due to its poor seed germination. This study focused on understanding the determinants of dormancy and identifying means of inducing maximum germination in Texas wintergrass toward making it more readily available for grazing systems. Scarification using sulfuric acid resulted in a significant improvement (≥50%) in the overall germination performance of the seeds. Chemical profiling of the seed coat identified diverse phenolic compounds, primarily in the form of flavonoids, which have been previously reported to induce seed dormancy in other plant species. Together, these results indicate the presence of exogenous dormancy in Texas wintergrass that prevents it from germinating even under optimum conditions. Treatment with low hydrogen peroxide (H2O2) titers in combination with scarification further increased seed germination up to 85%. This positive germination response is attributed to H2O2-induced weakening of the seed coat that makes it semipermeable, oxidation and leaching of phenolic inhibitors of germination, and hydrolysis of H2O2 that provides seeds with access to more water and O2. Additionally, treatment with low H2O2 concentrations within the first 24 h of water uptake downregulated abscisic aldehyde oxidase (AAO3) and upregulated abscisic 8′ hydroxylase (A8H1) expression. AAO3 converts abscisic aldehyde into abscisic acid (ABA), whereas A8H1 breaks down ABA to produce phaseic acid. Treatment with the phytohormones gibberellic acid (GA) and 6-benzylaminopurine (BAP) in combination with scarification also improved the germination performance of Texas wintergrass, with BAP producing better results than GA.