Abstract
Switchgrass (Panicum virgatum L.) is an emerging bioenergy crop in the US, but little has been done by breeders to improve its poor seed germination and slow and inconsistent establishment. The objective of this study was to evaluate the effects of divergent selection for seed weight on germination in three switchgrass populations over two cycles with and without a cold stratification treatment. Seed from switchgrass populations 9064202, ‘Carthage’, and ‘Timber’ was sorted into light and heavy weight classes via a gravity deck and germinated in a growth chamber. Seedlings were planted to the field in isolated crossing blocks. Seed from these blocks was sorted and germinated following a divergent selection scheme for a second cycle. Seed was harvested from all derived crossing blocks representing all cycles of selection and subjected to a cold or no stratification treatment and germinated in a growth chamber. One cycle of selection for heavy seed resulted in an increase in progeny seed weight in 9064202 and Carthage but not Timber. A second cycle of selection gave unexpected results, probably due to the effects of genetic drift. The effect of seed weight was not significant for germination percentage or germination rate index. Dormancy had a larger impact on overall germination and germination rate than seed weight in the populations tested. Therefore, selection efforts focused on reducing dormancy rather than increasing seed weight are likely to be more successful in improving overall germination and germination rate in switchgrass population 9064202 and cultivars Carthage and Timber.