An S-allele cDNA was cloned from pistils of 'McIntosh' apple (Malus ×domestica Borkh.). The allele, designated Si in Japan and S10 in Europe, is an S-RNase that is very similar (94%) to the S3-RNase at the deduced amino acid sequence level. This allele can be detected by amplification using the polymerase chain reaction (PCR) and specific primers, followed by digestion with restriction enzyme EheI. The S10 allele was discovered in 'Empire', 'Maypole', 'Shinano Red', 'Spencer', and 'Vista Bella'. The S-allele cDNAs sequenced to date are listed with their Japanese and European designations.