Characterization of the sour cherry strain of plum pox potyvirus
So far, cherry trees have been considered as resistant to plum pox potyvirus (PPV - EPPO A2 quarantine pest) infections. Experimental transmission of several isolates of PPV (from plum, peach, apricot) to Prunus avium and P. mahaleb showed that the virus remained localized to the infection site and became undetectable. However, it has been reported recently from Moldova that sour cherry (P. cerasus) was naturally infected with PPV (see EPPO RS 94/143). Infected trees showed characteristic chlorotic ringspot symptoms on leaves and depressions, necrosis and rings on fruit. Studies were carried out on this sour cherry strain using RT-PCR, molecular hybridization, nucleotide sequencing, ultrathin sectioning of infected tissues and graft transmission to different cherry rootstocks. Results showed that this virus is indeed plum pox potyvirus, although the sour cherry strain differs from other known strains of PPV (i.e. PPV-D and PPV-M type strains). The authors felt that the sour cherry strain should be considered as a prototype of a new group, the PPV-C group (cherry group). It was also observed that the virus is systemically distributed in P. cerasus, and can be found in infected leaf, bark, root, flower, fruit and seed tissues. PPV was detected by RT-PCR in anthers and pollen of infected trees and the authors stressed that this could be a source of virus dissemination, especially on germplasm material. In transmission experiments, the sour cherry strain was successfully transmitted by chip bud grafting to P. avium (sweet cherry) and P. mahaleb rootstocks. It can be recalled that natural infection of sweet cherry with PPV has recently been reported from southern Italy (see EPPO RS 94/144). Preliminary results of studies carried out by the authors tend to suggest that PPV from both sweet and sour cherry may represent an undescribed group of PPV. In addition, the sour cherry isolate can be transmitted to plum (P. domestica), and therefore appears not to be restricted only to cherry species, but may have the potential to infect other stone fruits. It was also pointed out that the infected cherry material in Moldova came from Russia, where PPV was then detected in sour cherry mother trees. The authors concluded by stressing the need to revise quarantine requirements for plum pox potyvirus, especially to prevent the introduction of PPV through movement of infected cherry germplasm.
Sources
Nemchinov, L.; Hadidi, A. (1996) Characterization of the sour cherry strain of plum pox potyvirus.
Phytopathology, 86(6), 575-580.