Switchgrass (Panicum virgatum L.) genotypes differ between coastal sites and inland road corridors in the Northeastern US

Authors: ECKER, GEOFFREY - University Of Connecticut; Zalapa, Juan; AUER, CAROL - University Of Connecticut

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2015
Publication Date: 6/30/2015
Publication URL: http://handle.nal.usda.gov/10113/61565
Citation: Ecker, G., Zalapa, J., Auer, C. 2015. Switchgrass (Panicum virgatum L.) genotypes differ between coastal sites and inland road corridors in the Northeastern US. PLoS One. 10(6). doi: 10.1371/journal.pone.0130414.

Interpretive Summary: The quest for renewable energy has led to the genetic modification of various C4 grasses to become dedicated biofuels feedstocks. However, the adaptability of these grasses and the introduction of novel traits have generated concerns about new weed problems or invasive species. In the case of switchgrass, breeding and genetic engineering (GE) have been used to advance switchgrass as a model biofuels feedstock and led to the recent approval of GE switchgrass in the U.S. These rapid advances have created a need for scientific information to develop predictive ecological risk assessments and effectively confine experimental field trials. Switchgrass is a native, perennial grass across Eastern and Central North America. Switchgrass has been divided into two ecotypes; individuals in the Lowland ecotype are usually tetraploid, while those in the Upland ecotype are either tetraploid or octaploid. Upland plants are associated with dry to moderate moisture habitats, while Lowland plants are found in both riparian and coastal flood plains. In the Northeastern region, the pre-settlement distribution of switchgrass is believed to have been a narrow zone along the coastal salt marsh. However, recent surveys in the Northeast found numerous switchgrass populations in road verges as much as 188 km from the coast raising questions about their origins, genetics, and dispersal in current and future climate regimes. 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. We identified a unique genotype in both the LISCL and road verges indicating the importance of preserving local switchgrass populations and genetic resources through seed collection programs and other actions. However, the abundance non-local genotypes, principally along road verges, suggest that they are well established in the area. This study supports the ecological risk assessments of switchgrass with novel traits by determining. This constitutes the first study on switchgrass genetics in this part of its distribution range.

Technical Abstract: 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.