Switchgrass as a bioenergy feedstock: advances in breeding and genomics research

Switchgrass (Panicum virgatum L), a native perennial of the North American prairie, possesses high biomass yield potential in marginal environments with limited input. It is an outcrossing tetraploid (2n = 4x = 36) with disomic inheritance. Previous research on cultivar improvement was focused primarily on herbage yield and forage digestibility. The decision of the U.S. Department of Energy Biomass Feedstock Development Program (NFDP) to develop switchgrass as a lignocellulosic bioenergy feedstock in the USA in the 1990s prompted a growing motivation for breeding and genomics research. The species is in early stages of domestication and current cultivars include mostly early releases for forage use that were selected directly from collected strains. Recent releases specifically for biomass feedstock have undergone one or two cycles of selection. As an outcrossing self-incompatible species, switchgrass possesses ample genetic diversity both between and within native populations. Conventional population improvement approaches such as recurrent restricted phenotypic selection (RRPS) are effective in improving forage yield and digestibility. Hybrids between different populations also demonstrated heterosis for key feedstock traits. However, genetic gains per year from selection using conventional approaches are low due to perennial growth habit and low heritability of important traits. Genomic approaches could be helpful in improving selection gain. Significant efforts have been placed in developing genomics resources. Genetic linkage maps were published and a large number of DNA-based markers were developed. Whole-genome sequencing is near completion, and the genetic bases of inheritance of key feedstock traits are being investigated. New insights into the molecular mechanisms will enable tailoring more efficient cultivar breeding approaches in the future.