Identification of S haplotypes in cabbage inbred lines (Brassica oleracea var. capitata L.)

• A total of 16 known S haplotypes were observed in 107 cabbage inbred lines.
• The recombination between the S and kinase domains of the SRK gene was observed.
• For haplotype test, the SRK S domain sequence is more important than kinase domain.
• S15 was the most common haplotype with a frequency of 21.62% in this study.

Knowledge of the S haplotypes of cabbage breeding lines is very important for breeders when assuring cross-compatibility between lines. In the present study, PCR amplification using gene-specific primers derived from the S locus receptor kinase (SRK) and S locus cysteine protein (SCR) genes, followed by sequencing and BLAST analysis, allowed the molecular identification of the S haplotypes of 111 cabbage inbred lines. The identified S haplotypes were confirmed by fluorescence microscopy after pollination in those inbred lines with the same flowering time. Using this method, class I and class II haplotypes were detected in 56 and 55 inbred lines, respectively. Sixteen known S haplotypes were observed in 107 inbred lines; however, four class I lines could not be identified by sequence analysis. Recombination between the sequences encoding the S and kinase domains of the SRK protein was observed in four inbred lines indicating that the sequence of the SRK S domain is more important than that of the SRK kinase domain for identification of S haplotypes. In the study, S15 was the most common haplotype, with a frequency of 21.62%, while S13, S16 and S35 were the lowest frequency haplotypes (0.90%). Most inbred lines with class I haplotypes showed stronger self-incompatibility, and self-compatible inbred lines were mainly from S5 and S15. The distribution of S haplotypes in cabbage inbred lines will be useful for the breeding objectives and may guide future development of new self-compatible inbred lines and F1 hybrids.