Evaluation, Validation, and Application of Sex-Specific Molecular Marker in Kiwifruit (Actinidia spp.)

The genus Actinidia is primarily functionally dioecious, and early sex identification plays a crucial role in improving breeding efficiency and reducing production costs. In this study, the accuracy of three sex-linked molecular markers (SyGI [Shy Girl], FrBy [Friendly Boy], and SmY1) in sex identification was evaluated in various Actinidia species. The selected marker products were subsequently cloned and sequenced in six wild Actinidia species. Ninety-six wild A. chinensis chinensis accessions and 74 A. chinensis deliciosa accessions, most of which were wild, with only one cultivated, were used for comprehensive primer validation. Thirty-three juvenile A. chinensis chinensis hybrid seedlings were used for practical application tests. The results showed that the marker SyGI accurately identified the sex of 20 samples from six Actinidia species and 96 A. chinensis chinensis accessions with 100% reliability. For Actinidia chinensis deliciosa, the identification accuracy reached 98.65%. Sequence analysis revealed that SyGI shared the highest similarity with the male-specific genomic region. Furthermore, SyGI achieved 100% accuracy in identifying the sex of 33 juvenile A. chinensis chinensis individuals. The findings confirm that the SyGI marker possesses high accuracy, strong specificity, and broad applicability, making it a valuable tool for kiwifruit breeding programs. The cloned sequences from wild Actinidia species also provide important references for future research on the mechanisms of sexual evolution and determination.