Location: Dairy Forage ResearchTitle: Natural hybrids and gene flow between upland and lowland switchgrass Author
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2011
Publication Date: 10/31/2011
Publication URL: http://handle.nal.usda.gov/10113/56377
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. Natural hybrids and gene flow between upland and lowland switchgrass. Crop Science. 51:2626-2641. 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. Due to repeated ice ages, all types of switchgrass have been forced into narrow refuge zones on a cycle of approximately 100,000 years. We have shown that up to 25% of all switchgrass plants in our collection have a partially mixed-up genome, showing evidence of past hybridizations between different types of switchgrass. These plants are of great potential value to plant breeders, geneticists, and restorationists in learning why individual switchgrass plants have specific and sometimes narrow adaptation zones, as well as helping to create switchgrass populations that are resilient against impending climate change.
Technical Abstract: Switchgrass (Panicum virgatum L.) is a perennial grass native to the North American tallgrass prairie and savanna habitats and is broadly adapted to the central and eastern USA. Upland and lowland ecotypes represent the two major taxa within switchgrass, which have distinct, but overlapping distributions. The purpose of this study was to survey a broad array of putative upland and lowland accessions for the possible presence of natural hybrids or hybrid derivatives and evidence of historic gene flow between the two ecotypes. All plants were classified as upland, lowland, or intermediate based on visual assessment of phenotype, using large nurseries of known upland or lowland plants as controls. A total of 480 plants were surveyed for 19 simple sequence repeat (SSR) markers and sequenced using five cpDNA segments. Genetic structure analysis revealed 21 individuals with strong evidence for inter-taxa hybrid origin and another 25 individuals with moderate evidence for inter-taxa hybrid origin. All but two of these individuals originated from remnant populations of the Central or Eastern Gulf Coast or along the Atlantic Seaboard, a region that is populated with significant quantities of both upland and lowland ecotypes. We propose the Central and Eastern Gulf Coast glacial refuge as the primary center of origin and diversity for switchgrass, with the Western Gulf Coast as the secondary center of origin and diversity.