Characterization of the ribosomal DNA units in two related Prunus species (P. Cerasifera and P. Spinosa).

The genetic relationships between two Prunus species, involved in rootstock breeding, were examined at the level of the ribosomal RNA genes. Twenty clones of P. cerasifera, a diploid species, and 12 clones of P. spinosa, a tetraploid wild species, were studied. The use of three heterologous ribosomal DNA probes covering different regions of the ribosomal tandem repeats enabled us to construct restriction maps for EcoRI and BamHI. We identified two unit types (unit I and unit II) in P. cerasifera. In P. spinosa, P. cerasifera units were present in addition to a third ribosomal unit type (unit III). These results appeared to confirm previous cytological studies (Salesses 1973) indicating that one of the genomes in P.spinosa has homology with the one from P. cerasifera.