Impact of ploidy on biomass yield of upland switchgrass (Panicum virgatum L.): A meta-analysis

Authors: CASLER, MICHAEL - Retired ARS Employee

Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2022
Publication Date: 1/1/2023
Citation: Casler, M.D. 2023. Impact of ploidy on biomass yield of upland switchgrass (Panicum virgatum L.): A meta-analysis. Genetic Resources and Crop Evolution. 70:1115-1122. https://doi.org/10.1007/s10722-022-01489-1.
DOI: https://doi.org/10.1007/s10722-022-01489-1

Interpretive Summary: Switchgrass is a potentially valuable crop for sustainable production of bioenergy from biomass conversion. Breeding, genetics, and genomics of switchgrass are the basis for improving switchgrass varieties for perennial biomass production systems. Before any research can be conducted in these areas, breeders and geneticist must determine the desired chromosome number or ploidy to form the basis for the breeding and genetics program. The two choices are: tetraploid (28 chromosomes) or octoploid (56 chromosomes). There is no consensus as to which is better: the octoploid has a longer history of research, but the tetraploid has simpler genetics, making it easier to conduct complex genetic studies. This research showed that there is a small biomass yield advantage to the octoploid, mainly in higher yielding environments. This advantage is not due to a biological or genetic difference in chromosome number, but more likely due to a longer history of selection and breeding at the octoploid level. These results will help switchgrass breeders and geneticists to better understand the implications of choosing to conduct research with switchgrass varieties at either the tetraploid or octoploid chromosome number.

Technical Abstract: Switchgrass (Panicum virgatum L.) has two ecotypes that are genetically and phenotypically distinct: upland and lowland. Furthermore, the upland ecotype has two distinct cytological races: tetraploid and octoploid. This study was undertaken to determine if there is a difference between the tetraploid and octoploid cytotypes of the upland ecotype for biomass yield. The study utilized data from 15 published studies, including 145 field trials and 446 trial-years of data for which a tetraploid vs. octoploid statistical comparison was possible. Of the 145 trials, 34 showed a statistical advantage of octoploid over tetraploid, averaging 34% for these trials, compared to 11% over all 145 trials. Octoploids tended to be more responsive to favorable environments, with a significantly higher linear response to increasing mean biomass yield. The octoploid cytotype is more common across the natural landscape and within germplasm collections aimed at breeding new cultivars. Furthermore, formal selection and breeding of switchgrass has been ongoing for longer at the octoploid level compared to the tetraploid level. Thus, the biomass yield advantage of octoploid switchgrass compared to the tetraploids, for the upland ecotype, is more likely an anthropogenic phenomenon, resulting from historically larger population sizes, greater collection activity, and more long-term selection pressures.