S genotyping and S screening utilizing SFB gene polymorphism in Japanese plum and sweet cherry by dot-blot analysis

Most Rosaceae fruit trees such as Japanese plum and sweet cherry have a gametophytic self-incompatibility (GSI) system controlled by a single S locus containing at least two linked genes with multiple alleles, i.e., S-RNase as a pistil determinant and SFB (S-haplotype-specific F-box gene) as a candidate for the pollen S determinant. For identification of S genotypes, many methods based on polymerase chain reaction (PCR) utilizing polymorphism in length of the S-RNase and SFB gene have been developed. In this study, we developed two dot-blot analysis methods for S-haplotype identification utilizing allele-specific oligonucleotides based on the SFB-HVa region, which has high sequence polymorphism. Dot-blotting of allele-specific oligonucleotides hybridized with digoxigenin-labeled PCR products allowed S genotyping of plants with nine S haplotypes (S-a, S-b, S-c, S-e, S-f, S-h, S-k, S-7 and S-10) in Japanese plum and ten S haplotypes (S-1, S-2, S-3, S-4, S-4′, S-5, S-6, S-7, S-9 and S-16) in sweet cherry (dot-blot-S-genotyping). In addition, dot-blotting of PCR products of SFB probed with the allele-specific oligonucleotides, occasionally utilizing competitive hybridization, was successful in screening for a desirable S haplotype in sweet cherry (dot-blot-S-screening).