Dihaploid Stocks of Switchgrass Isolated by a Screening Approach

Abstract

Manipulation of ploidy in switchgrass has potential to accelerate inbred production and to provide insight about genome structure through either sequencing or cytogenetic approaches. We have identified two dihaploid individuals isolated from among the progeny of a controlled cross between two individuals of the cultivars Alamo and Kanlow. The dihaploid lines were initially distinguished from the parental lines by their reduced heterozygosity and were subsequently confirmed through estimation of C values by flow cytometry and chromosome counts of metaphase root tip squash preparations. These plants are functionally sterile, with floral bracts that remain closed and inviable pollen. They can be easily distinguished from tetraploid individuals by their reduced stature, smaller epidermal cell size, and lower number of chloroplasts per guard cell. Aberrant meiosis in these individuals is evidenced by a lack of regular pairing at diakinesis and metaphase I and suggests that the nonhomologous genomes are distinct from one another. The reduced genome size of these dihaploids will facilitate basic genome studies and genetic analyses that are impossible or problematic in polyploid accessions.

Population genomic variation reveals roles of history, adaptation and ploidy in switchgrass

“…The switchgrass plants used in this study represent collections from remnant habitats and from cultivated varieties which are seed increases of source-identified collections that have undergone few generations of amplification and are considered good representations of the native genetic variation from original collection locations (Zalapa et al 2011). These sample included two di-haploids, which have only one copy of each chromosome from each sub-genome (Young et al 2010) and should have no heterozygosity. We also included one sample each of P. amarum, P. amarulum , and P. anceps .…”

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

“…Ploidy also represents a significant pollination barrier, as interploidy hybridizations are both rare and difficult to achieve even under controlled conditions (Martinez-Reyna and Vogel 2002). Gene flow from 8x to 4x can occur in switchgrass by polyembryony and parthenogenesis (Young et al 2010) and likely occurs from 4x to 8x by 2n gametes (Harlan and de Wet 1975), but both of these processes occur at low frequencies. However, because ice ages occur on a 100-kyr cycle, long-term proximal exposure increased the opportunities for intertaxa hybridization within these refugia, so fairly rare events could lead to unusual phenotypes and genotypes in the frequencies observed in our studies.…”

“…Octoploid (8x) is the most common ploidy level for both wild accessions and cultivars, followed by tetraploid (4x). Diploid (2x) forms are extremely rare and have only recently been re-discovered following intensive screening under highly controlled conditions (Young et al 2010;Price et al 2010, unpublished data). Hexaploid (6x) switchgrass plants have been frequently reported in the literature, but have not been confirmed in recent studies (Costich et al 2010).…”

Complete Switchgrass Genetic Maps Reveal Subgenome Collinearity, Preferential Pairing and Multilocus Interactions

“…Limited gene flow appears possible between different cytotypes suggested by DNA content variation within collection sites and seed lots (Nielsen 1944;Hultquist et al 1997;Narasimhamoorthy et al 2008). True diploids appear to be rare (Nielsen 1944;Young et al 2010). Multivalents in meiosis have not been observed in tetraploids or F1 hybrids between upland and lowland tetraploids, although rare univalents occurred (Barnett and Carver 1967;Martinez-Reyna et al 2001).…”