Molecular identification of S-alleles associated with self-incompatibility in apple (Malus spp.) genotypes

Gametophytic self-incompatibility, governed by the S-locus in apple (Malus spp.) plays a vital role for pollination and fruit set. The identification and cloning of RNases has enabled the use of molecular techniques to characterize S-genotypes in apple cultivars. To identify the S-alleles associated with self-incompatibility, allele specific primers were tested using PCR, evaluating eight apple genotypes. A total of 6 pollen incompatibility groups in apple genotypes were identified among eight accessions by PCR based S-allele typing analysis. Eight putative S-alleles (S1, S2, S7, S19, S21, S23, S24 and S26) were identified with S1S7, S1S23, S1S24, S2S26, S19S24 diploid and S1S21S24 triploid combinations that had not previously been identified from apple cultivars. The molecular allele typing system of S-genotypes based on PCR is a useful and rapid method for identifying new S-alleles and incompatibility groups in apple and the present results enabled the characterization of eight apple cultivars with respect to S-allele composition which is an important and preliminary step for pollination management and hybridization in apple breeding programmes.