Changes in Mean and Genetic Variance During Two Cycles of Within-family Selection in Switchgrass

Authors: Casler, Michael

Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2009
Publication Date: 2/22/2010
Citation: Casler, M.D. 2010. Changes in Mean and Genetic Variance During Two Cycles of Within-family Selection in Switchgrass. BioEnergy Research. 3:47-54.

Interpretive Summary: Switchgrass is a potentially important plant for development of cellulosic bioenergy feedstock production. Biomass yield is the most important biological factor limiting the commercial development and deployment of switchgrass as a cellulosic bioenergy feedstock. For this reason, we have undertaken the objective of increasing biomass yield of switchgrass by genetic selection and breeding. This paper reports on progress from two generations of selection for increased biomass yield. Selection increased biomass yield by an average of 1/3 Ton/acre and survival by an average of 6%. The results were consistent for two evaluation sites representing two different soil types and two hardiness zones. These results will be of value to other switchgrass breeders and agronomists, illustrating the potential for breeding progress, and to switchgrass growers and extension personnel who will be interested in new varieties to be developed from this research.

Technical Abstract: Switchgrass (Panicum virgatum L.) is a candidate for cellulosic bioenergy feedstock development. Because biomass yield is the most important biological factor limiting the commercial development and deployment of switchgrass as a cellulosic bioenergy feedstock efforts must be undertaken to develop improved cultivars. The objectives of this study were (1) to conduct two cycles of within-family selection for increased biomass yield in WS4U switchgrass and (2) to simultaneously evaluate progress from selection relative to the mean of the original WS4U population. Each of the 150 WS4U families was subjected to phenotypic selection for vigor, seed production, and disease resistance. The mean of all families increased relative to the original WS4U population by 0.36 Mg ha-1 cycle-1 for biomass yield and 3.0 % cycle-1 for ground cover. Gains were uniform across two diverse evaluation locations, indicating that selection gains were robust relative to some variation in hardiness zone and soil type. Two cycles of within-family selection led to a homogenization of the diverse families, creating novel recombinations and reducing the family genetic variance to near zero. It is hypothesized that selection and recombination has led to replication of favorable alleles across pedigrees with differing genetic backgrounds, increasing the likelihood of including these favorable alleles in the progeny of future selections. The rate of genetic progress is expected to increase in future cycles of selection with a combination of within-family phenotypic selection and half-sib progeny testing of selected families.