genetic linkage map of the cultivated strawberry (Fragaria x ananassa) and its comparison to the diploid Fragaria reference map

The cultivated strawberry, Fragaria x ananassa, is the most economically-important soft-fruit species, but few practical molecular tools for the purpose of marker assisted selection currently exist. As a precursor to the development of such tools, a genetic linkage map was developed from a F₁ population comprising 174 seedlings derived from a cross between two F. x ananassa cultivars, 'Redgauntlet' x 'Hapil'. The resultant map is composed of 315 molecular markers--218 microsatellites, 11 gene-specific markers and 86 AFLP and RAPD markers--and spans 3,116 cM. In total, 69 linkage group fragments were recovered, more than the 56 linkage groups expected for the cultivated strawberry, however, all fragments contained a transferable marker that could be associated with one of 56 linkage group scaffolds. The female (Redgauntlet) and male (Hapil) linkage maps are composed, respectively of 170 loci in 32 linkage groups covering 1,675.3 cM and 182 loci in 37 linkage groups covering 1,440.7 cM, with 37 markers common to both maps. The maximum number of markers in one linkage group was 15, the minimum was two. All linkage groups resolved contained at least one transferable marker (SSR or gene-specific) that had been mapped on the diploid Fragaria reference map (FV x FB), and therefore all linkage groups could be identified as homologous to one of the seven diploid Fragaria linkage groups. When marker order was compared to the diploid Fragaria reference map, effectively complete colinearity was observed. However, the occurrence of duplicated loci on homologues of linkage groups FG1 and FG6 provided evidence of a putative chromosomal duplication or translocation event in Fragaria. The development of this linkage map will facilitate the study and dissection of QTL associated with traits of economic importance such as disease resistance and fruit quality, and provides a foundation for the development of markers for the purpose of marker assisted breeding and selection in the cultivated strawberry, F. x ananassa.