Application of SCAR markers to self-incompatibility genotyping in breeding lines of radish (Raphanus sativus L.)

Self-incompatibility (SI) prevents self-fertilization by inhibiting the pollen tube growth of self-pollen. Molecular analysis has revealed that the S locus comprises a number of genes, such as the S-locus glycoprotein (SLG), the S-locus receptor kinase (SRK), and SP11 (SCR). Although molecular markers related to those genes have been developed, a simple S-haplotype detecting method has not been reported due to the highly polymorphic and relatively small coding regions. In this study, the sequence characterized amplified region (SCAR) markers were used to establish an efficient radish genotyping method. We identified the S-haplotypes of 192 radish accessions using 19 different markers, which proved to be highly reliable. The accessions were assigned to 17 types of S-haplotypes, including 8 types of SRKs and 9 types of SLGs. Since the developed SCAR markers are based on their gene sequences, we could easily identify the S-haplotypes by a single specific band, with the highest frequencies detected for SLG 5, SRK 1, and SLG 1, in order. Among the tested markers, the SLG 1, SRK 1, and SRK 5 markers exhibited high reliability, compared to phenotypic results. Furthermore, we identified the seven types of unreported SLGs using SLG Class -I and -II specific markers. Although the developed SCAR markers still need to be improved for the genotyping of all S-haplotypes, these markers could be helpful for monitoring inbred lines, and for developing the MAS in radish breeding programs.