`Jonathan' apple is a lower-potency pollenizer of `Topred' than `Golden Delicious' due to partial S-allele incompatibility

Summary`Topred' is one of the main apple cultivars in Israel. Since `Topred' exhibits full self incompatibility, its fruit production is totally dependent on cross pollination. The two commercial pollenizers of `Topred' in Israel are `Golden Delicious' and `Jonathan'. In the study presented here, the potential of these two pollenizers was determined. In two consecutive seasons, it was found that the rate of fruit-set and fruit yield were significantly higher in the rows of `Topred' adjacent to the `Golden Delicious' as compared with the rows adjacent to the `Jonathan'. PCR analysis of the S-alleles, a polymorphic gene locus, determining the outcome of pollination, revealed that `Jonathan' and `Topred' share allele S9. PCR-S-allele analysis of progeny seedlings revealed that in `Jonathan' only S7, the unshared allele, took part in fertilization, whereas both alleles of `Golden Delicious' (S2,S3) participated at equal rates. Thus, the lower potency of `Jonathan' as a pollenizer of `Topred' is due, at least ...