Variants of Hop stunt viroid Associated with Mulberry Vein Clearing in Iran

Samples of mulberry leaves showing vein clearing, yellow speckle and leaf deformation symptoms were collected in the Fars Province of Iran. Grafting of buds from affected trees onto a number of healthy mulberry rootstocks resulted in transmission of the pathogen 40 days postinoculation. Likewise, mechanical inoculation of sap from affected leaves resulted in induction of similar symptoms in mulberry seedlings. Total nucleic acid was extracted from leaf tissues and subjected to reverse transcription polymerase chain reaction (RT-PCR) using Hop stunt viroid (HSVd) and Citrus exocortis viroid (CEVd)-specific primers, followed by sequencing of PCR products. RT-PCR with HSVd primers amplified a 302- or 305-bp product from affected samples, but none from healthy plants. CEVd was not detected in affected trees. HSVd was also found in graft- and mechanically inoculated plants. Sequence analyses showed three variants of HSVd in symptomatic mulberries related to plum and peach variants of this viroid with 94.9% identity, but with only 93% identity to Lebanese and Italian mulberry isolates. This is the first report of HSVd associated with vein clearing in mulberry in Iran.