Determination of S-haplotypes of Japanese plum (Prunus salicina Lindl.) cultivars by PCR and cross-pollination tests

S-haplotypes of Japanese plums were determined by PCR and cross-pollination tests. Five novel S-RNase genes corresponding to S-1- to S-11- haplotypes were identified by PCR with an S-RNase gene-specific primer set, Pru-C2 and PCE-R. Thirteen new S-genotypes (S-haplotype combinations) were found in the 19 cultivars used. Several cultivars had the same S-genotypes. Partial genomic DNAs for six S-RNase genes were cloned and sequenced. Deduced amino acid sequences contained conserved regions among the rosaceous S-RNases. Cross-pollination and pollen-tube growth tests revealed that pollen-tube growth was arrested in the upper middle part of stylar tissue in the crosses between the self-incompatible cultivars with the same S-genotypes. These results showed the first evidence for the existence of S-RNase-based cross-incompatibility in Japanese plum.