Switchgrass population and cold–moist stratification mediate germination

Switchgrass (Panicum virgatum L.) breeding and selection have enhanced the agronomic qualities of this species as a crop for forage and bioenergy applications. Previous work has characterized variation in phenotypic traits (e.g., survival, biomass yield, and cell wall carbohydrates) among wild and cultivated populations. Despite the importance of low dormancy to the establishment of a productive switchgrass stand, there is little information characterizing the dormancy of selectively bred cultivars vs. wild populations of switchgrass. The objectives of this study were to use growth chamber experiments to quantify germination vs. dormancy (confirmed by tetrazolium tests) of eight wild and four cultivar populations and evaluate the relationship between seed size and germination. While cultivars generally showed higher germination than wild populations, there was marked variation in germination among wild populations; for those with lower germination, the ungerminated fraction comprised mostly live (i.e., dormant) seeds. These data led us to perform a subsequent experiment testing the application of a seed treatment, cold-moist stratification, on a subset of eight populations representing the wide variation in germination observed in the first experiment. Cold-moist stratification substantially increased germination, but the magnitude of the effect varied among populations. Populations with higher dormancy showed a much larger increase in germination after cold-moist stratification. These data clearly show that seed dormancy in wild populations can be easily overcome by cold-moist stratification in the short term and breeding and selection in the long term.