Identification and Characterization of an Italian Isolate of Pear Blister Canker Viroid

A small RNA with the structural property characteristic of viroids has been isolated frotn a pear plant {P8) showing superficial cracks or splits on the bark of the secondary branches and horizontal deep bark splits on the trunk. Polyacrylamide gel electrophoresis analysis of the P8 isolate revealed that the viroid had the same electrophoretic mobility as pear blister canker viroid (PBCVd). P8 RNA reacted in molecular hybridization assays with the specific PBCVd cRNA probe, and its reverse transcript polymerase chain reaction amplified fragment was the same size as the amplified fragment of PBCVd. Sequence analysis of the P8 isolate revealed only five changes in its primary structure when compared with the standard PBCVd isolate P2098T. Four of these changes were present also in P47A and P1914T PBCVd isolates previously characterized in Spain. The viroid associated with PS pear can thus be considered a PBCVd isolate. This is the first report of PBCVd in a pear orchard in Italy.