Changes in Mean and Genetic Variance During Two Cycles of Within-family Selection in Switchgrass
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Changes in Mean and Genetic Variance During Two Cycles of Within-family Selection in Switchgrass Michael D. Casler
Published online: 28 January 2010 # US Government 2010
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.
M. D. Casler (*) USDA-ARS, U.S. Dairy Forage Research Center, 1925 Linden Dr, Madison, WI 53706–1108, USA e-mail: [email protected]
Keywords Panicum virgatum L . Biomass yield . Breeding . Biofuel crops
Introduction Switchgrass (Panicum virgatum L.) is a candidate for cellulosic bioenergy feedstock development in some parts of the USA and Canada. Switchgrass is widely adapted to many habitats east of the North American Rocky Mountains. Feedstock development of switchgrass was initiated by the U.S. Department of Energy in 1992, with expansion to USDA-ARS in 2002, and later addition of significant Department of Energy competitive grant programs [16]. With the increase in research on this native species, and subsequent improvements in management efficiency, public and commercial interest in switchgrass production has increased accordingly [16]. Early adoption and deployment of switchgrass for bioenergy production has been based on existing cultivars, developed as seed increases of prairie remnant populations or from a limited number of selection cycles in forage breeding programs [19]. Switchgrass cultivars are highly photoperiodic and vary considerably in adaptation to local climatic conditions, resulting in regional deployment patterns that re
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