Replication of Grapevine leafroll-associated virus-7 (GLRaV-7) by Cuscuta Species and Its Transmission to Herbaceous Plants.
Grapevine leafroll-associated virus-7 (GLRaV-7) was transmitted from an Albanian grapevine accession to Tetragonia expansa by the parasitic dodder Cuscuta reflexa and to Nicotiana occidentalis by Cuscuta europea. Cuscuta campestris was infected by GLRaV-7 but could not transfer the virus to an experimental host. Transmission of the virus was verified by reverse transcription-polymerase chain reaction (RT-PCR) from total nucleic acid (TNA) and double-stranded RNA (dsRNA) extracts from all five plant species. DsRNA extractions separated on agarose gels showed strong visible bands corresponding to high-molecular-weight virus genome and to subgenomic RNA. GLRaV-7 was maintained in C. reflexa, C. campestris, T. expansa, and N. occidentalis for more than 4 years. Infected T. expansa and the Cuscuta species remained symptomless while N. occidentalis showed severe symptoms leading to stunting and decline of the plants. Quantitative PCR showed great differences in the titer of GLRaV-7 between the tissues of its natural and experimental host plants. This is the first report on a virus of the Closteroviridae that was successfully transmitted to an herbaceous plant by dodder. Virus replication could be demonstrated in Cuscuta. Both the new experimental hosts of GLRaV-7 and Cuscuta allowed extraction of dsRNA for further characterization of the viral genome, which previously required grapevine scraping of phloem. This is time-consuming and does not always lead to satisfactory results. These alternative hosts of GLRaV-7 facilitate nucleic acid extractions and could be used as model plants for etiological studies.