First report of Pear blister canker viroid in Malta

In 2006, a tissue-printing hybridisation (TPH) method was used to test for the presence and spread in Malta of Pear blister canker viroid (PBCVd) (Hernàndez et al.,1992). The survey was mainly addressed to test PBCVd infection in the local pear cv Bambinella, which is of special interest for the country. A total of 113 trees grown near Rabat (Malta) were assayed. Although none of them showed any visible symptom, 14 (ca.12%) tested positive for PBCVd. Seven of these trees were used as source material for graft-inoculating 14 seedlings of the pear indicator LA62 (two seedlings for each infected accession). Six months later, PBCVd was detected in all inoculated seedlings by molecular hybridization and by RT-PCR assays, using the specific primers designed by Malfitano et al. (2003), and the expected 315 bo cDNA amplcon was sequenced. Negative results were obtained when the same analyses were done on LA62 seedlings which, in parallel experiments, had been graft-inoculated with material from TPH-negative Bambinella trees grown in the same area. Like naturally PBCVd-infected trees, seedlings successfully infected by graft-inoculation did not show any symptom. Altogether, these data show that PBCVd occurs in symptomless cv Bambinella pears in Malta and further validate the TPH method for large scale surveys of PBCVd infections. To our knowledge, this is the first report of PBCVd in Malta.