Distribution of S haplotypes in commercial cultivars of Brassica rapa

Self-incompatibility in Brassicaceae plants is sporophytically controlled by a single multi-allelic locus (S locus), which contains at least three highly polymorphic genes expressed in the stigma (SLG and SRK) and in the pollen (SCR/SP11). Using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis with SLG-specific primer pairs, the S haplotypes of F₁ hybrid and open-pollinated commercial cultivars of Brassica rapa were identified. The number of S haplotypes detected in the F₁ hybrid cultivars of Chinese cabbage, komatsuna, pak-choi, turnip, open-pollinated cultivars of Chinese cabbage and turnip were 9, 9, 4, 11, 13 and 12, respectively. Nine of them had different PCR-RFLP profiles from those of the S-tester lines that determined the SLG sequences. Four SLG sequences in the F₁ hybrid cultivars were determined and named S⁵³, S⁵⁴, S⁵⁵, and S⁵⁶, respectively. It is demonstrated that the PCR-RFLP analysis using specific primer pairs of SLG and SRK is useful for identification of the S haplotypes, in both, S homozygous and S heterozygous plants of B. rapa. The possibility of using this method routinely in breeding programmes, and in the evaluation of F₁ hybrid seed purity, is discussed.