Germination and Emergence in Three Switchgrass Cultivars Divergently Selected for Seed Weight.

Switchgrass (Panicum virgatum L.) is a C4 perennial warm-season grass native to the eastern two-thirds of the United States and chosen as a model bioenergy feedstock species by the Department of Energy.  However, poor germination resulting in slow and inconsistent establishment and heavy weed competition is a major limitation to the successful adoption of this bioenergy crop. It has been demonstrated that larger and heavier switchgrass seed has improved germination and emergence.  However, no studies have been conducted that investigate the effects of several cycles of selection for seed weight on switchgrass germination and emergence. The objective of this study was to determine the effects of divergent selection for seed weight and cold stratification on germination and emergence in three switchgrass cultivars (Timber, Carthage, and 9064202). A gravity deck was used to separate seed of three switchgrass cultivars into heavy and light weight classes for two cycles of selection. Three replicates of seed from all selection cycles were germinated in a growth chamber for 28 d and compared for germination and emergence to determine if selection for heavy seed improves germination in switchgrass.  Effects of cycle and cultivar were significant.  Overall germination ranged from 91% in, heavy, cycle 2 Carthage seed to 26.3% in cycle 1 9064202 seed.  In general, seed from cycle 2 had higher germination percentages than cycle 1.  In lowland cultivar Timber, selection for lighter seed resulted in lower germination percentages while selection for heavier seed resulted in higher germination percentages.  Germination rates were highest in heavy, cycle 2 9064202 seed and lowest in light, cycle 1 9064202 seed.  In all cultivars tested, germination rates were highest in heavy seed, intermediate in unsorted seed, and lowest in light seed.  Based on these results, continued cycles of selection for heavy seed may result in seed with improved germination.