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K.S. Lewers, S.M.N. Styan, S.C. Hokanson and N.V. Bassil

Although simple sequence repeat (SSR) markers have been developed for species in the closely related genera Fragaria L. (strawberry) and Rubus L. (raspberry and blackberry), the number of SSRs available is insufficient for genetic mapping. Our objective was to use and compare multiple approaches for developing additional SSRs for Fragaria and Rubus. The approaches included: the development of SSRs from GenBank sequences from species of varied relatedness to Fragaria and Rubus and identified with two different data-mining methods (BLAST and SSRIT); the evaluation of some previously published SSRs designed from related species; and the development of SSRs from a genomic library made from F. ×ananassa Duschene ex Rozier `Earliglow'. When an SSR was developed from a known gene sequence, the location of the repeat in the gene was determined to evaluate the effect on amplification and polymorphism detection. Cross-generic amplification between closely related Fragaria and Rubus as well as transference from species of varied relatedness to Fragaria and Rubus also was evaluated and indicated limited transference within the subfamily Rosoideae. However, development of SSRs for Fragaria and Rubus from Rosa L. (rose) and Rosaceae genera outside Rosoideae was not efficient enough to be practical for new map development. SSRIT was superior to BLAST for identifying GenBank sequences containing repeats. SSRs developed from repeats found in either the 5′UTR (80% polymorphic) or 3′UTR (85% polymorphic) were most likely to detect polymorphisms, compared with those developed from coding regions (30%). SSRs developed from the genomic library were only slightly superior to GenBank-derived SSRs in their ability to detect polymorphisms.

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Thomas M. Davis, Laura M. DiMeglio, Ronghui Yang, Sarah M.N. Styan and Kim S. Lewers

The cultivated strawberry, Fragaria ×ananassa Duchesne ex Rozier, originated via hybridization between octoploids F. chiloensis (L.) Mill. and F. virginiana Mill. These three octoploid species are thought to share a putative genome composition of AAA`A'BBB`B'. Diploid F. vesca L., is considered to have donated the A genome. Current attention to the development of a diploid model system for strawberry genomics warrants the assessment of simple sequence repeat (SSR) marker transferability between the octoploid and diploid species in Fragaria L. In the present study, 23 SSR primer pairs derived from F. ×ananassa `Earliglow' by genomic library screening were evaluated for their utility in six diploid Fragaria species, including eight representatives of F. vesca, four of F. viridis Weston, and one each of F. nubicola (Hook. f.) Lindl. ex Lacaita, F. mandshurica Staudt, F. iinumae Makino, and F. nilgerrensis Schltdl. ex J. Gay. SSR primer pair functionality, as measured by amplification success rate (= 100% - failure rate) in each species, was ranked (from highest to lowest) as follows: F. vesca (98.4%) > F. iinumae (93.8%) = F. nubicola (93.8%) > F. mandshurica (87.5%) > F. nilgerrensis (75%) > F. viridis (73.4%). The extent to which these octoploid-derived SSR primer pairs generated markers that could be added to the F. vesca linkage map also was assessed. Of the 13 F. ×ananassa SSR markers that segregated codominantly in the F. vesca mapping population, 11 were assigned to linkage groups based upon close linkages to previously mapped loci. These markers were distributed over six of the seven F. vesca linkage groups, and can serve as anchor loci defining these six groups for purposes of comparative mapping between F. vesca and F. ×ananassa.