Molecular characterization of a tombusvirus isolated from diseased peer trees in Southern Italy

A tombusvirus first isolated in 1991 in Apulia (southern Italy) from pear trees (Pyrus communis L.) showing reduced growth, reddish discolourations and premature shedding of the leaves, was again recovered from symptomatic plants and characterized. Agarose gel analysis of extracts from systemically infected Nicotiana benthamiana plants showed the presence of two major and one minor RNA species with a size compatible with that of genomic RNA and of monomeric and dimeric defective interfering (DI) RNAs of tombusviruses. RNA was extracted from purified virus particles. All these RNA species were cloned, sequenced and shown to have a typical tombusviral structural organization. The most prominent cytopathological feature of N. benthamiana infected cells was the presence of peroxisome-derived multivesicular bodies. In immunodiffusion tests this virus proved to be serologically related with some tombusviruses, the closest being Grapevine Algerian latent virus (GALV), but showed wide molecular differences with all sequenced members of the genus. This virus was successfully transmitted to pear seedlings and rooted cuttings that were still symptomless five months after inoculation. Thus, it was given the provisional name of Pear latent virus (PLV)