Switchgrass (Panicum virgatum L.) Genotypes Differ between Coastal Sites and Inland Road Corridors in the Northeastern US

Switchgrass (Panicum virgatum L.) is a North American grass that exhibits vast genetic diversity across its geographic range. In the Northeast, switchgrass was restricted to a narrow zone adjacent to the coastal salt marsh, but current populations inhabit inland road verges raising questions about their origin and genetic composition. These questions are important because switchgrass with novel traits is being cultivated as a feedstock for biofuel production, and gene flow could impact the genetic resources and distribution of local populations. This study was designed to determine if: 1) switchgrass plants collected in the Long Island Sound Coastal Lowland (LISCL) coastal Level IV ecoregion represent native populations, and 2) switchgrass plants collected from road verges in the adjacent inland regions were related to local coastal populations or switchgrass from other geographic regions. The study used 18 simple sequence repeat (SSR) markers to infer the genetic relationships between 123 collected switchgrass plants and a reference dataset consisting of 28 cultivars representing ecotypes, ploidy levels, and lineages from North America. Results showed that 88% of 86 plants collected in the coastal LISCL were most closely aligned with the Lowland tetraploid genetic pool. Among this group, 59 coastal plants were similar to, but distinct from, all L4x cultivars in the reference database leading to a new genetic sub-population denominated Southern New England Lowland Tetraploids (SNELT). In contrast, 70% of 37 plants collected in road verges in the inland ecoregions were most similar to two Upland octoploid cultivars; only 22% of roadside plants were Lowland tetraploid. These results suggest that cryptic, introduced genotypes exist in road verges and that gene flow from biofuels plantations could contribute to further changes in the genetics of unique, natural switchgrass populations in the Northeast.