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

Abstract

Switchgrass (Panicum virgatum), a central and Eastern USA native, 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 1.5-1 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.

Variability of nuclear DNA content and agromorphological characteristics of switchgrass (Panicum virgatum L.) germplasm in Lithuania

“…Previous studies have reported that the lowland populations are exclusively tetraploid, whereas the upland type can vary in ploidy (tetraploid, heksaploid and octoploid), both within and among populations (Narasimhamoorthy et al, 2008;Costich et al, 2010;Zalapa et al, 2011, Zhang et al, 2011Lu et al, 2013). Our results also showed that switchgrass collection varied in ploidy between populations.…”

“…A number of researchers have reported the plants of tetraploid populations to be taller compared to those of octoploid populations (Cortese et al, 2010;Zhang et al, 2011 a).…”

“…These two groups of ecotypes differ in both agrobiological and phenological characteristics (Casler, 2012). Some researchers maintain that such division into two separate groups is inaccurate (Missaoui et al, 2006;Zhang et al, 2011 a), because of the existence of the intermediate (hybrid) group of ecotypes for which stable level of ploidy is not inherent (Vogel, Mitchell, 2008;Zhang et al, 2011 b). It is believed that an increase in chromosome number in polyploid plant populations enhances the level of heterozygosity and creates prerequisites for better adaptation of the species, i.e.…”

Dedicated Herbaceous Biomass Feedstock Genetics and Development

“…The research demonstrated the existence of at least 10 distinct types of switchgrass, ranging from highly drought-tolerant ecotypes of the Great Plains to highly heat-tolerant types of the Atlantic Seaboard. The work further indicated that all unique types of switchgrass originated in particular regions in the southern USA where switchgrass survived numerous Ice Ages [130,131]. Collaborative work between ARS and other institutions has developed a mechanism to routinely assay thousands of switchgrass genotypes for DNA markers representing coding regions with 169,000 unique genes [53,129].…”

Comparative Relationships and Chromosome Evolution in Switchgrass (Panicum virgatum) and Its Genomic Model, Foxtail Millet (Setaria italica)

“…Evolutionary events are numbered (in parenthesis), and each number is followed by Y, N, or U indicating whether this rearrangements took place (Y), did not take place (N), or could not be assessed (U) in switchgrass. Event (1) is a nested chromosome insertion, event (10) is a reciprocal translocation, and the remaining events are intrachromosomal inversions P. hallii and P. virgatum has been dated to approximately 5.3 MYA [33], tetraploid P. virgatum must have been formed in the past 5 MY. This number is in close agreement with divergence estimates based on 6,800 bp of sequence data of 6 MYA for the divergence of the switchgrasses A and B genomes and 3.8 MYA for the split between the closely related A genome of switchgrass and E genome of Panicum rudgei (B. Bahri and K.M.…”