Surveying Grassland Islands: The genetics and performance of Appalachian Switchgrass (Panicum virgatum L.)

Authors: TILHOU, NEAL - University Of Wisconsin; Casler, Michael

Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2021
Publication Date: 1/7/2022
Citation: Tilhou, N., Casler, M.D. 2022. Surveying Grassland Islands: The genetics and performance of Appalachian Switchgrass (Panicum virgatum L.). Genetic Resources and Crop Evolution. 69:1039-1055. https://doi.org/10.1007/s10722-021-01282-6.
DOI: https://doi.org/10.1007/s10722-021-01282-6

Interpretive Summary: Switchgrass is one of the energy grass candidates for development of perennial biomass systems to supply feedstock for bioenergy production. Significant breeding efforts are required to make switchgrass production systems more economically sustainable. One approach to improving sustainability is to identify late-flowering plants with sufficient winter hardiness to survive in the northern USA, where they can continue to grow and accumulate biomass up to killing frost. Most efforts have focused on collection of plants from the deep south, where winter hardiness is severely lacking. This project focused on a broad evaluation of plants collected in the mid-Appalachian region, an area that has never been surveyed for use in switchgrass breeding programs. While many plants collected in this region had high winter hardiness, they were generally early flowering, making them largely unfit for use in developing biomass cultivars, but potentially useful for developing forage cultivars. Three sites contained late-flowering plants with strong winter hardiness, being potentially useful for switchgrass breeding programs in the northern USA.

Technical Abstract: The interior Southeastern United States could contain novel germplasm for the bioenergy crop switchgrass due to its diverse habitats and geographic location between genetic subpopulations (Atlantic, Midwest, and Gulf). Collections from this region could accelerate breeding progress, contribute to conservation efforts, and improve understanding of isolated grasslands in the region. This study located 22 sites in the Midsouth region and obtained 1,521,210 single nucleotide polymorphism markers of 202 individuals through genotype by sequencing. Individuals were evaluated for flowering time, winter survival, tiller number, and height. Comparison to a national diversity panel revealed that branches of two major subpopulations occur in the region with two levels of polyploidy: Atlantic tetraploids and Midwest octoploids. Two locations contained admixed octoploid individuals with Midwest and Gulf genetics. Field performance of the Midwest octoploids conformed with prior reported performance of the Midwest subpopulation, although three sites contained promising late flowering traits. The Atlantic tetraploids had moderate winter survival, short stature, and anomalously early flowering. Atlantic populations mostly occurred in marginal sites and their morphological and flowering time adaptations may be a nutrient conservation strategy. Demographic inference of historical effective population size variation in a subset of tetraploid locations indicated widespread multi-century declines in effective population size. This pattern is consistent with isolation of these switchgrass communities from larger populations and is further supported by inbreeding within the populations (FI=0.18). The genetic diversity and range of colonized habitats documented in this study provides a valuable resource for future breeding and conservation using locally adapted germplasm.