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

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.