S-RNase genotyping and incompatibility group assignment by PCR and pollination experiments in Japanese plum

Most Japanese plum-type cultivars are self-incompatible and cross pollination is necessary to ensure fruit set. In this study, the S-RNase genotype and the incompatibility group of 68 Japanese plum-type cultivars were determined by PCR amplification of the S-RNase gene. The S-RNase genotype of 50 cultivars is first reported here and five new Japanese plum S-RNase alleles (So, Sp, Sq, Sr, Ss) were identified. The results obtained, together with information compiled from previous studies, allowed describing 12 new incompatibility groups (VIII-XIX). The self-incompatibility of several cultivars and the cross-compatibility among different incompatibility groups were verified by self- and cross-pollination experiments followed by observation of pollen tube growth. Five cultivars behaved as self-compatible, but two of them do not have the Se allele, which has been correlated with self-compatibility. Thus, additional sources of self-compatibility different from Se appear to be involved in Japanese plum self-compatibility.