Characterization of S-alleles of 'SCS421 Carolina' new self-fertile pear cultivar

Pear harbors the gametophytic self-incompatibility system as a genetic control to prevent self-fertilization and avoid inbreeding depression. This system is governed by the multi-allelic S-locus that codes for RNases that act on the plant pistil and prevents the development of the pollen tube when the S-allele present in the pollen grain is same as the one present in the diploid tissue of the pistil. In such cases and in the absence of parthenocarpy, the natural production of fruits and seeds does not occur. The new 'SCS421 Carolina' cultivar has shown high natural fruit setting, even under unfavourable climatic conditions, suggesting the possibility that it contains the S-4(sm) mutant allele for self-fertility. This work aimed to determine the S-alleles of the 'SCS421 Carolina' cultivar and its possible parents in order to confirm their pedigree based on the segregation of S-alleles. Also, the self-fertilization rate was evaluated through the isolation of flowers, preventing cross-pollination. Genotyping of S-alleles was performed by genetic markers using five primer sets associated with the pear S-locus. The results indicated that 'SCS421 Carolina' has S3S4sm alleles, with 'Housui' (female) and 'Osanijisseiki' (male) as parents, and the average self-fertility rate evaluated through the protection of floral clusters was 50.5% because it carries the S-4(sm) self-fertility allele.