A MOLECULAR METHOD FOR S-ALLELE IDENTIFICATION IN APPLE BASED ON ALLELE-SPECIFIC PCR

cDNA sequences corresponding to two self-incompatibility alleles (S-al leles) of the apple cv 'Golden Delicious' have previously been describ ed, and now we report the identification of three additional S-allele cDNAs of apple, one of which was isolated from a pistil cDNA library o f cv 'Idared' and two of which were obtained by reverse transcription- PCR (RT-PCR) on pistil RNA of cv 'Queen's Cox'. A comparison of the de duced amino acid sequences of these five S-allele cDNAs revealed an av erage homology of 69%. Based on the nucleotide sequences of these S-al lele cDNAs, we developed a molecular technique for the diagnostic iden tification of the five different S-alleles in apple cultivars. The met hod used consists of allele-specific PCR amplification of genomic DNA followed by digestion of the amplification product with an allele-spec ific restriction endonuclease. Analysis of a number of apple cultivars with known S-phenotype consistently showed coincidence of phenotypic and direct molecular data of the S-allele constitution of the cultivar s. It is concluded that the S-allele identification approach reported here provides a rapid and useful method to determine the S-genotype of apple cultivars.