New insights on Plum pox virus present in Chile

Plum pox virus (PPV) was first detected in Chile in December 1992. Preliminary identification showed mainly the presence of strain D. Official surveys developed by the Plant Protection Agency (Servicio Agricola y Ganadero, SAG) and by our laboratory during the last five years, indicated that some samples obtained from apparently healthy trees were positive to ELISA and to RT-PCR assays using commercial polyclonal antibodies and specific primers for the 3 ' genomic terminal region, respectively. Recently collected symptomatic and non-symptomatic peach samples of the central valleys of Chile were used for grafting on Prunus tomentosa and for direct virus purification. Propanol clarification followed by CsCl gradient banding allowed us to obtain fractions of purified particles in both cases, suitable for further molecular characterization. Electron microscopy of negatively stained viral fractions revealed the presence of potyviral-like particles surrounded by a lot of disrupted material, apparently of the same class. Entire particles were estimated to be about 750 nm in length with flexuous filamentous shape. Serological analysis showed poor reactivity to commercially available antibodies against known PPV strains. At moment, we are working on the amplification and cloning of some portion of the genome of these viral particles looking for differences with known strains of PPV to understand the basis of the absence of symptoms.