QTL analysis and trait dissection in ryegrasses (Lolium spp.)
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概要
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The majority of traits of interest to pasture grass breeders, such as dry matter yield, forage quality and environmental stress tolerance, show continuous phenotypic variation and are controlled by a variable number of quantitative trait loci (QTL). Substantial advances have been made in the genetic improvement of plant populations through artificial selection of quantitative traits. Most of this selection has been on the basis of observable phenotype, without knowledge of the genetic architecture of the selected characteristics. In major crop species, the development of high-resolution genetic maps has made it possible to identify the chromosomal regions, or in some instances, the individual sequence variants that are responsible for trait variation. There have been relatively few reports to date of QTL analysis for agronomic traits in forage grasses, due to the absence of a sufficiently well developed genetic map. An enhanced molecular marker-based genetic linkage map of perennial ryegrass (Lolium perenne L.) has recently been constructed through the activities of the International Lolium Genome Initiative (ILGI), using the p150/112 one-way pseudo-testcross reference population (Jones et al., 2002a,b). Two genetic mapping populations of perennial ryegrass have been independently developed as successors to the p150/112 population, and have been aligned to the reference map using common markers (Armstead et al., 2002, 2004; Faville et al., 2005). These genetic maps contain functionally-associated molecular marker information through the inclusion of gene-associated cleaved amplified polymorphic sequences (CAPS) markers, and both restriction fragment length polymorphism (RFLP) and simple sequence repeat (SSR) markers from expressed sequence tags (ESTs), respectively. In addition, high- density molecular marker-based genetic maps have also recently been constructed for other species of Lolium and Festuca (Alm et al., 2003; Inoue et al., 2004a; Warnke et al., 2004; Saha et al., 2005). Genetic markers and maps are consequently available for detailed dissection of complex phenotypes to resolve the locations of pleiotropic and interacting genetic factors. In this chapter, recent results from QTL analysis of the p150/112 reference population and another populations of perennial ryegrass are reviewed, and are related to comparative genomics studies with otherPoaceae species.http://www.wageningenacademic.com/molecular
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