Self-incompatibility Alleles of Apple Cultivars and Advanced Selections

The S -alleles of 55 apple ( Malus × domestica Borkh.) cultivars and selections were determined using an allele-specific polymerase chain reaction (PCR) amplification system for 11 different S -alleles ( S 2, S 3, S 4, S 5, S 7, S 9, S 24, S 26, S 27, S d, S f). Four cultivars had S -alleles different than those predicted by their parentage. Three commercial cultivars of unknown pedigrees had S -genotypes that suggested `Delicious' and `Golden Delicious' were the parents. S -genotyping results supported controlled pollination test results. The genotypes of the five triploid cultivars examined were consistent with the unreduced gamete being contributed by the female parent. Although a large number of S -genotypes is available in apple, artificial selection or repeated use of the same cultivars as parents appears to have significantly restricted the number of compatibility groups associated with commercial clones. In controlled reciprocal crosses between two cultivars of known S -genotypes, the segregation of S -genotypes and S -alleles was 1:1:1:1, the ratio expected for random pairing of alleles.