S-allele determination of Pillnitzer apple cultivars

Apple (Malus sp.) has an S-RNase-based gametophytic self-incompatible system ruled by a multi-allelic S-locus. Self-pollination of apple cultivars is hindered and pollinators with at least one different S-allele are required for successful fertilization. To determine the S-allele combination in cultivars and advanced breeding clones bred in Dresden-Pillnitz, 69 genotypes from Pillnitz and 65 cultivars, clones, and wild apple species accessions were analyzed. Cultivars with known S-alleles were selected for comparison of the data. The alleles S₂, S₃, S₅, S_16b, and S₂₄ were present in 64 of the genotypes bred in Pillnitz. The most abundant alleles in the other genotypes were S₂, S₃, S₅, and S₉. Only one S-allele could be determined for the wild species accessions M. ×arnoldiana MAL0004, M. floribunda 821, and ‘Russian Seedling’, and the determination of S-alleles for M. fusca MAL0045 failed. A new S-allele, tentatively designated S_Regia, was detected in 'Regia'. The analyzed S-allele combination of some cultivars differed from those published, e.g. S₂S_16b genotype was here determined for 'Pinova' in contrast to S₂S₉ genotype assigned in the literature. Knowledge about the S-allele status of the cultivars helps in the selection of a suitable pollinator.