Genetic Diversity, Plant Adaptation Regions, and Gene Pools for Switchgrass

Abstract

Switchgrass (Panicum virgatum L.) is a perennial grass native to the North American tallgrass prairie and broadly adapted to the central and eastern USA. Transfer of germplasm throughout this region creates the potential of contaminating local gene pools with genes that are not native to a locale. The objective of this study was to identify structural patterns and spatial variation for molecular markers of switchgrass populations from the northern and central USA. Forty‐six prairie‐remnant populations and 11 cultivars were analyzed for random amplified polymorphic DNA (RAPD) markers. Although there was significant population differentiation, little of this variation was associated with geographic regions. A small amount of population differentiation was associated with hardiness zones and ecoregions, suggesting that a recent proposal to use these two criteria for defining plant adaptation regions has merit for defining gene pools and seed‐transfer zones of switchgrass. Cultivars of switchgrass cannot be differentiated from prairie‐remnant populations in the northern and central USA on the basis of RAPD markers, indicating that they are still highly representative of natural germplasm. Seed sources of switchgrass can be moved considerable distance within hardiness zones and ecoregions without causing significant contamination, pollution, swamping, or erosion of local gene pools.

Post-glacial evolution of Panicum virgatum: centers of diversity and gene pools revealed by SSR markers and cpDNA sequences

“…These forces resulted in a balance between migration, drift, and selection, creating phenotypic diversity across a broad landscape (McMillan 1959;Casler et al 2007b), but allowing continued migration to balance the effects of drift, maintaining large effective population sizes across a broad landscape. Even with the loss of more than 99% of the tallgrass prairie and savanna ecosystems to habitat loss and fragmentation (Stubbendieck et al 1991), massive amounts of genetic diversity have been preserved in nearly every accession that we have sampled (Casler et al 2007a;Zalapa et al 2011).…”

“…Some limited gene flow between the two refugia could explain the presence of accessions that represent admixtures between the southern Great Plains lineage and eastern Gulf Coast lineage, but this would likely have required a more-or-less continuous distribution of lowland switchgrass all along the Gulf Coast during glacial maxima. Given the dominance of prevailing westerly winds as a mechanism of long-term pollen transport, it is easy to imagine that very small annual movements of pollen from western strains could eventually lead to admixtures in some eastern strains as hypothesized by Casler et al (2007a).…”

Genetic diversity in tetraploid switchgrass revealed by AFLP marker polymorphisms

“…They found little differentiation correlated with geography, but a small amount was associated with hardiness zones and ecotypes. Casler et al (2007) also reported that plants from the same region could be highly unrelated to each other. They further indicated that their markers could not distinguish between cultivars and remnant wild populations.…”

“…Past molecular marker studies on genetic diversity analysis in switchgrass include random amplified polymorphic DNA (RAPD; Gunter et al, 1996;Casler et al, 2007), restriction fragment length polymorphism (RFLP; Missaoui et al, 2006), and simple sequence repeats (SSRs; Narasimhamoorthy et al, 2008;Cortese et al, 2010). Gunter et al (1996) used RAPDs to assess the genetic diversity among and within 14 populations of switchgrass and to find markers that are useful for population identification.…”

“…Gunter et al (1996) used RAPDs to assess the genetic diversity among and within 14 populations of switchgrass and to find markers that are useful for population identification. Casler et al (2007) performed RAPDs on 46 remnant populations and 11 cultivars to discover if there was population differentiation and to evaluate possible correlations between genotypes, ecotypes, and geographic forms. They found little differentiation correlated with geography, but a small amount was associated with hardiness zones and ecotypes.…”