Location: Dairy Forage ResearchTitle: Post-glacial evolution of Panicum virgatum: centers of diversity and gene pools revealed by SSR markers and cpDNA sequences) Author
Submitted to: Genetica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2011
Publication Date: 7/23/2011
Publication URL: http://handle.nal.usda.gov/10113/56390
Citation: Zhang, Y., Zalapa, J.E., Jakubowski, A.R., Price, D.L., Acharya, A., Wei, Y., Brummer, E.C., Kaeppler, S.M., Casler, M.D. 2011. Post-glacial evolution of Panicum virgatum: centers of diversity and gene pools revealed by SSR markers and cpDNA sequences. Genetica. 139:933-948. Interpretive Summary: Switchgrass is native to the tallgrass prairie and savanna ecosystems of the central and eastern USA. It is highly valued as a component in tallgrass prairie and savanna restoration and conservation projects and a potential bioenergy feedstock. One of our long term goals is to develop a system to classify all plants of switchgrass into regional gene pools that can be freely exchanged within plant adaptation regions, assuring that all varieties and strains are optimally adapted. We have identified 10 distinct lineages of switchgrass, some of which correspond to specific geographic regions. Southern switchgrasses, particularly those from Florida, Georgia, and the Carolinas, are by far the most diverse, both among and within collection sites. The southeastern USA is clearly the primary center of diversity for switchgrass, providing a source of highly unusual gene combinations for use by plant breeders in developing switchgrass cultivars with specific and broad regional adaptations, as well as some level of resistance or resiliency to climate change.
Technical Abstract: Switchgrass (Panicum virgatum) is native to the tallgrass prairie and associated ecosystems of the central and eastern USA. It is highly valued as a component in tallgrass prairie and savanna restoration and conservation projects and a potential bioenergy feedstock. The purpose of this study was to identify regional diversity, gene pools, and centers-of-diversity of switchgrass to gain an understanding of its post-glacial evolution and to identify both the geographic range and potential overlap between functional gene pools. We sampled a total of 384 genotypes from 49 accessions that included the three main taxonomic groups of switchgrass (lowland 4x, upland 4x, and upland 8x) along with one accession possessing an intermediate phenotype. We identified primary centers of diversity for switchgrass in the eastern and western Gulf Coast regions. Migration, drift, and selection have led to adaptive radiation in switchgrass, creating regional gene pools within each of the main taxa. We estimate that both upland-lowland divergence and 4x-to-8x polyploidization within switchgrass began approximately 1.5 to 1 M ybp and that subsequent ice age cycles have resulted in gene flow between ecotype lineages and between ploidy levels. Gene flow has resulted in “hot spots” of genetic diversity in the southeastern USA and along the Atlantic Seaboard, as well as maintained high levels of allelic richness throughout the range, facilitated by frequent and recurrent migration events across a broad landscape.