Characterization of the sour cherry strain of plum pox virus

Properties of the sour cherry isolate of plum pox virus (PPV) were investigated by reverse transcription-polymerase chain reaction (RT-PCR), restriction fragment length polymorphism (RFLP), molecular hybridization, nucleotide sequencing, ultrathin sectioning of infected tissue, and graft transmission to different cherry rootstocks. Analysis of RT-PCR-amplified cDNA product from infected tissue with primers for the 3' noncoding region (3'-NCR) of the PPV genome and molecular hybridization of the amplified product with a labeled PPV cRNA probe verified that the potyvirus infecting sour cherry trees (Prunus cerasus) in Moldova is an isolate of PPV. RFLP analysis of RT-PCR products from infected tissue with specific primers for the 3'-terminal region of the PPV coat protein (CP) gene revealed that the sour cherry isolate of PPV is a unique strain of PPV and a prototype of a new group that contains neither the RsaI nor the AluI restriction site. These results were confirmed by nucleotide sequencing analysis. Nucleotide sequencing of the 3'-NCR and the region coding for the 3'-terminal fragment of the PPV CP gene showed about 93% identity to that of other PPV isolates. RT-PCR assays of tissue extracts from three sour cherry cultivars demonstrated that sour cherry PPV was distributed systemically in sour cherry trees and infected leaf, bark, root, flower, fruit, and seed tissues. The virus was successfully transmitted by chip bud grafting to rootstocks of P. avium (sweet cherry) and P. mahaleb.