Complete Nucleotide Sequence and Properties of Raspberry Mottle Virus

During routine graft indexing of Rubus clones at the USDA-ARS Horticultural Crops Research Laboratory in Corvallis, Oregon, a ‘Glen Clova’ plant that originated in Scotland induced severe symptoms including stunting and apical necrosis when grafted on ‘Munger’ black raspberry (Rubus occidentalis). Cloning of viral dsRNA obtained from the plant and sequence analysis indicated the presence of a novel virus, a member of the Closteroviridae and possibly additional viruses. Detection protocols developed against the closterovirus were used and identified the virus in breeding and field material from Washington State as well as several additional raspberry clones from Scotland. Graft indexing of selection ‘WSU-991’ on R. occidentalis induced mottling symptoms and was free of other known raspberry viruses. The virus was thus temporarily designated as Raspberry mottle virus (RMoV). The complete nucleotide sequence of the virus has been obtained and exceeds 17 kilobases. Phylogenetic analysis indicated that RMoV is closely related to members of the Closterovirus genus, the aphid-borne closteroviruses. The genome organization is an intermediate between Citrus tristeza virus and Beet yellows virus with two putative leader proteases and a conserved array of open reading frames at the 3’ proximal terminus. Currently, additional graft indexing tests are in progress to examine the possibility that RMoV is the causal agent of Raspberry leaf mottle or Raspberry leaf spot diseases previously identified in Rubus. INTRODUCTION Several virus and virus-like agents infect Rubus spp. (Converse, 1987). Most of those agents are asymptomatic in commercial cultivars due to the tolerance introduced in the breeding process. Losses from these latent infections cannot be estimated easily when symptoms develop in the field in plants infected with multiple viruses. In these cases, losses are substantial, and multiple infections can even cause plant death. Since several of the agents that infect Rubus remain uncharacterized, grafting onto indicators is routinely used for detection of viruses. A raspberry plant ‘Glen Clova’ (GC-8) that originated at Scottish Crops Research Institute (SCRI), Scotland and was maintained in an insect-free screenhouse at the Horticultural Crops Research Laboratory (HCRL) in Corvallis, Oregon caused severe symptoms when grafted onto black raspberry ‘Munger’. The symptoms included mottling, stunting and apical necrosis, typical of raspberry mosaic disease (RMD), one of the most important viral diseases of Rubus. RMD was first described in the 1920s and graft-transmissible agents were associated with it in the 1950s. Four virus and graft-transmissible agents are now associated with the disease: Black raspberry necrosis virus, Black Rubus yellow net virus, Raspberry leaf mottle virus (RLMV) and Raspberry leaf spot virus (RLSV) (Converse, 1987) with the latter two being uncharacterized at the molecular level. Given the importance and the complexity of the disease, we decided to investigate the agents that were present in the GC-8 plant. Using double stranded RNA (dsRNA) as a template for shotgun cloning, we identified three novel viruses in the GC-8 plant (Martin and Tzanetakis, 2008). This communication presents data towards the characterization of one of these viruses that was named Raspberry mottle virus (RMoV). This novel virus was found in several plants including breeding and field material from Washington State as well as in plants that Proc. XI IS on Small Fruit Virus Diseases