Characterization of Polymorphic Microsatellites in Strawberry and Their Transferability to Other Genera in the Rosaceae Family

We investigated the transferability of 20 Fragaria vesca microsatellite primer pairs to 13 Fragaria vesca accessions, six Fragaria species and ten commercially important species in Rosaceae. Genetic diversity studies were carried among 16 diploid Fragaria accessions using these polymorphic microsatellites. The average number of alleles amplified for a polymorphic locus was 4.7 with maximum being 8.0 and minimum being 3.0. Observed heterozygosity ranged from 0.00 to 0.84 with an average of 0.28. Expected heterozygosity ranged from 0.33 to 0.91 with an average of 0.76. Power of discrimination varied from 0.43 to 0.92 with an average of 0.78. Transferability of microsatellites to F. orientalis (4x) and F. Ã ananassa (8x) was high, i.e., 18 (90%) primers produced amplicons.

Cross species amplification within Rosaceae using these primers showed limited transference. Four microsatellites showed amplification for different species in Rosaceae. Products generated by UDF-003 and UDF-018 primers were sequenced. Sequencing results for UDF-018 showed that three species, i.e., Pyrus calleryana, Prunus persica and Rubus idaeus contained the expected microsatellite whereas another four, i.e., Cotoneaster salicifolius, Rosa rugosa, Amelanchier arborea and Potentilla fruticosa had conserved regions resulting in generation of amplicons. For UDF 003, Spirea xbumalda and Prunus persica did not contain a microsatellite although there was some sequence similarity with Fragaria. Size homoplasy, i.e., alleles of identical size with different numbers of repeats within the SSR was observed among Fragaria and Rosaceae species for primer UDF-018, suggesting a need for caution when interpreting SSR variation from band migration in the absence of DNA sequences.