Abstract: A new S-RNase gene was identified in white pear ( Pyrus bretschneideri) by PCR - RFLP, DNA sequencing analysis and cross pollination tests. The fragment length of PCR amplification using primers specific for S₁-RNase to S₉-RNase, similar to that of S₈-RNase, was around 450 bp. RFLP and DNA sequence
analyses revealed that the two genes had great variations in introns and hypervariable (HV) regions. The nucleotide size of intron of this new gene was 252 bp, whereas that of S₈-RNase was merely 234 bp. By comparing the amino acids (AA) of the HV regions between the new S-RNase gene and S₈-RNase, this new gene had substitutions of 10AA and deletion of 1AA, respectively. Nevertheless, it showed a high identity to S₁₂-RNase that we previously identified in white pear, only 1 bp was substituted in the HV region, and 10 bp were substituted or deleted in the around regions. Based on our current results, the new S-RNase gene was named as S₁₉-RNase ( accession number in GenBank: AY250987). The results of recip rocal cross pollination tests
between pear cultivarswhose S genotypes have been determined and those containing S₁₉-RNase further confirmed that the isolated fragment was a new S-RNase gene.

Key words: Pyrus bretschneideri, Self-incompatibility, S-allele, Gene isolation