MOLECULAR CHARACTERIZATION OF TURKISH ISOLATES OF PEAR BLISTER CANKER VIROID AND ASSESSMENT OF THE SEQUENCE VARIABILITY OF THIS VIROID
S. Yesilcollou, S. Minoia, E.M. Torchetti, S. Kaymak, M. Gumus, A. Myrta, B. Navarro, F. Di Serio
A survey of the presence of Pear blister canker viroid (PBCVd) in pear trees in Turkey was carried out by tissue print hybridization. Four out of 74 trees (5.4%) from a pear germplasm collection tested positive and this result was confirmed by RT-PCR and sequencing. Molecular characterization of the Turkish PBCVd isolates from four different local pear cultivars, together with multiple sequence alignments and phylogenetic analyses including all PBCVd sequences reported previously, provided an insight in the sequence variability of this viroid and showed that: (i) a total of 98 polymorphic positions distributed throughout the molecule are present in PBCVd genomic RNA; (ii) some regions with presumed relevant functions are strictly preserved and, (iii) the geographic origin of the isolates and the host species apparently have a bearing on the sequence variability of the viroid. This study records the presence of PBCVd in Turkey and confirms that its geographic distribution has been underestimated, most likely because the majority of infected pear cultivars are symptomless.