Occurrence of Hop Stunt Viroid in Mulberry (Morus alba) in Lebanon and Italy

The presence of Hop stunt viroid (HSVd) was detected using RT-PCR and Northern blot hybridization in five of 60 samples from symptomless mulberry trees (Morus alba) collected in Italian and Lebanese orchards in July 2010. Infection levels were c. 10% in Lebanese and 8% in Italian samples. Nucleotide alignments showed that sequences of the mulberry HSVd isolates shared 95-96% identity with those of the same viroid occurring elsewhere. In a phylogenetic tree, mulberry HSVd isolates clustered together with those of HSVd-citrus, regardless of their geographical origin. This is the first report of infection in mulberry trees by HSVd.