Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/1996
Publication Date: N/A
Interpretive Summary: Plum pox disease (Sharka) is caused by plum pox virus (PPV). Sharka is the most important viral disease of stone fruit trees in Europe and the Mediterranean region. It has not been reported from the United States. Among stone fruits, cherry trees have been considered resistant to PPV infection. We have discovered and characterized a new strain of PPV that naturally infect sour cherry trees systemically in Moldova. This strain i This strain is significantly different from known strains of PPV and has the potential to infect other stone fruits. Scientists and quarantine personnel who are working on viral diseases of stone fruits should be informed of this new strain of PPV because of its potential threat to the stone fruit industry world-wide. Currently, national and international quarantine agencies such as APHIS, European Plant Protection Organization (EPPO), North American Plant Protection Organization, etc. do not require testing for PPV in cherry germplasm because it has been assumed that this germplasm is free of PPV. To protect the stone fruit industry in the U.S. and other countries from this new strain of PPV, quarantine regulations in the U.S. as well as other countries should be changed to prevent the introduction of PPV through the international movement of infected cherry germplasm.
Technical Abstract: 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 tree (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.