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

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% cyclefor 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.

Breeding for Biomass Yield in Switchgrass Using Surrogate Measures of Yield

“…Essentially, a 1-year delay would defeat the whole purpose of this selection scheme. Strictly from a historical standpoint, we already know that "Godzilla" selection (PS) as described above [7], selection for later flowering time [11], and selection for spaced-plant biomass [2] are all effective for increasing biomass yield of sward plots. However, the demonstrated inefficiency of these methods compared to direct selection for biomass yield in this population brings us full circle to the dilemma of the best way forward.…”

“…Despite the advantages offered by using row plots or spaced plants (increased selection intensity and cycle time reduced from 4 to 2 years), indirect selection was less efficient than HSF selection on a family mean basis, even with a 10 times increase in selection intensity. Conversely, when two selection trials are established concomitantly, one to measure biomass yield of sward plots and one to measure biomass, heading date, or anthesis date of individual plants, as was done by [7], all of these options demonstrated expected gains greater than HSF for biomass yield selection alone, with spaced-plant biomass and row-plot heading date giving the greatest expected gains.…”

“…Clonal propagation of individual genotypes is prohibitive in switchgrass, so sward plot evaluations require seed produced from either full-sib or half-sib matings. Usually, these matings must occur in the field in order to generate sufficient seed for field trials at a minimum of two locations [7]. All of these are reasons that sward-plot field trials are seldom used in switchgrass breeding.…”

Dedicated Herbaceous Biomass Feedstock Genetics and Development

“…Thus, diversity must be restored by introducing new germplasm. Maintaining genetic diversity within the families is critical in preserving the capacity to generate new greater-yielding and quality options dedicated to either bioenergy platform [17,110].…”

Variability of nuclear DNA content and agromorphological characteristics of switchgrass (Panicum virgatum L.) germplasm in Lithuania

“…The world switchgrass collection includes commercial varieties, breeding lines and two distinct groups of wild ecotypes -the upland and the lowland, which differ not only in agrobiological and phenotypic characteristics but also in ploidy level (Alexopoulou et al, 2008;Casler, 2010). There is information about agrobiological characteristics of switchgrass varieties, chromosome number in them and their suitability for combustion.…”