A functional S-allele, 'Sg', in the wild apple possessing a single amino acid, S-RNase 'Sg'-RNase', different from 'Sg-RNase' in Malus x domestica cultivars

S3-, S5-, S9- (=Sc-), Sf-, Sg- and Sh (=S24)-alleles in the wild apple were deduced by using S-allele-specific-polymerase-chain reaction (PCR)-restriction fragment length polymorphism (RFLP) analyses. Within the alleles, the deduced amino acid sequence of Sg'-RNase in Sg-allele of Malus transitoria differed by one amino acid from that of Sg-RNase in Sg-allele of M. x domestica 'Indo'. From the cross pollination analysis of M. transitoria and M. x domestica 'Indo', and S-allele-specific-PCR-RFLP analyses of their progenies, it was indicated that the pistil Sg'-RNase in M. transitoria rejected the pollen of Sg-allele from 'Indo'. A difference of one amino acid within the RHV region produced by natural mutation was not enough to generate a new S-allele. This is the first report in the literature concerning S-allele diversification in the apple.