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

'Topred' is one of the main apple cultivars in Israel. Since 'Topred' exhib its full self incompatibility, its fruit production is totally dependent on cross pollination. The two commercial pollenizers of 'Topred' in Israel ar e 'Golden Delicious' and 'Jonathan'. In the study presented here, the poten tial. 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 compar ed 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 pro geny seedlings revealed that in 'Jonathan' only S7, the unshared allele, to ok part in fertilization, whereas both alleles of 'Golden Delicious' (S2,S3 ) participated at equal rates. Thus, the lower potency of 'Jonathan' as a p ollenizer of 'Topred' is due, at least in part, to semi-compatibility betwe en the two cultivars.