Bin mapping of genomic and EST-derived SSRs in melon (Cucumis melo L.)

We report the development of 158 primer pairs flanking SSR motifs in genomic (gSSR) and EST (EST-SSR) melon sequences, all yielding polymorphic bands in melon germplasm, except one that was polymorphic only in Cucurbita species. A similar polymorphism level was found among EST-SSRs and gSSRs, between dimeric and trimeric EST-SSRs, and between EST-SSRs placed in the open reading frame or any of the 5'- or 3'-untranslated regions. Correlation between SSR length and polymorphism was only found for dinucleotide EST-SSRs located within the untranslated regions, but not for trinucleotide EST-SSRs. Transferability of EST-SSRs to Cucurbita species was assayed and 12.7% of the primer pairs amplified at least in one species, although only 5.4% were polymorphic. A set of 14 double haploid lines from the cross between the cultivar Piel de Sapo and the accession PI161375 were selected for the bin mapping approach in melon. One hundred and twenty-one SSR markers were newly mapped. The position of 46 SSR loci was also verified by genotyping the complete population. A final bin-map was constructed including 80 RFLPs, 212 SSRs, 3 SNPs and the Nsv locus, distributed in 122 bins with an average bin length of 10.2 cM and a maximum bin length of 33 cM. Map density was 4.2 cM/marker or 5.9 cM/SSR.