Self- and inter-(in)compatibility relationships of new interspecific hybrids of Japanese plum

The Japanese plum cultivars currently grown do not correspond to a pure species, but are hybrids derived from interspecific crosses carried out from the original species (Prunus salicina Lindl.) with other Prunus species. Several new cultivars from breeding programs of different countries have been introduced in the last years. However, the pollination requirements of most of these new cultivars are unknown. In this work, the pollination requirements of 34 interspecific plum × apricot hybrids have been established by combining the determination of the self-(in)compatibility and S-allele genotyping of each accession with the monitoring of flowering dates. Self-(in)compatibility was determined by the observation of pollen tube growth in the pistil of self-pollinated flowers by fluorescence microscopy. The S-genotypes of all accessions were identified by amplifying the S-RNase alleles using PCR analysis with primers developed in sweet cherry. Three accessions behaved as self-compatible and 28 as self-incompatible, whereas the other three accessions showed unclear results. The self-incompatible accessions were assigned into ten Incompatibility Groups. The incompatibility relationships and flowering dates of the accessions described in this work will be useful for growers for selecting adequate pollinizers for each self-incompatible accession, and for breeders for selecting parents for new crosses.