Abstract
Switchgrass (Panicum virgatum) has been identified as a promising cellulosic biofuel crop in the United States. Construction of a genetic linkage map is fundamental for switchgrass molecular breeding and the elucidation of its genetic mechanisms for economically important traits. In this study, a novel population consisting of 139 selfed progeny of a northern lowland genotype, NL 94 LYE 16X13, was used to construct a linkage map. A total of 2493 simple sequence repeat markers were screened for polymorphism. Of 506 polymorphic loci, 80.8% showed a goodness-of-fit of 1:2:1 segregation ratio. Among 469 linked loci on the framework map, 241 coupling vs. 228 repulsion phase linkages were detected that conformed to a 1:1 ratio, confirming disomic inheritance. A total of 499 loci were mapped to 18 linkage groups (LG), of which the cumulative length was 2085.2 cM, with an average marker interval of 4.2 cM. Nine homeologous LG pairs were identified based on multi-allele markers and comparative genomic analysis. Two clusters of segregation-distorted loci were identified on LG 5b and 9b, respectively. Comparative analysis indicated a one-to-one relationship between nine switchgrass homeologous groups and nine foxtail millet (Setaria italica) chromosomes, suggesting strong homology between the two species. The linkage map derived from selfing a heterozygous parent, instead of two separate maps usually constructed for a cross-fertilized species, provides a new genetic framework to facilitate genomics research, quantitative trait locus (QTL) mapping, and marker-assisted breeding.
Highlights
Switchgrass (Panicum virgatum) has been identified as a promising cellulosic biofuel crop in the United States
The mapping population consisted of 139 individuals randomly selected from 279 inbreds derived by selfing NL94, which was identified as a typical tetraploid lowland ecotype (2n = 4X = 36) based on the detection of the 49 bp deletion in trnL-UAA intron, a special marker for switchgrass classification between lowland and upland (Missaoui et al 2006)
The decision to use 139 progeny was dictated by our genotype-detecting equipment, which enables the organization of the entire mapping population in two 66-well plates plus a small marker screening panel including seven individuals and the parent
Summary
Switchgrass (Panicum virgatum) has been identified as a promising cellulosic biofuel crop in the United States. Its genetic diversity has historically been used for soil conservation, forage production, game cover, and as an ornamental grass It has been selected as the model herbaceous species for use as a dedicated bioenergy feedstock crop (McLaughlin and Kszos 2005). Switchgrass is a wind pollinated and largely self-incompatible species (Talbert et al 1983; Taliaferro et al 1999; Martinez-Reyna and Vogel 2002) Because of this sexually out-crossing mode of reproduction, all released cultivars were populations composed of genetically heterozygous individuals. Molecular tools and genomic information are limited in switchgrass and need to be developed These new and quickly evolving technologies have extensive potential if incorporated into and coupled with conventional genetic improvement and breeding programs for developing superior cultivars
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