CHARACTERIZATION OF THREE NOVEL VIRUSES INFECTING RASPBERRY

Abstract

During routine graft indexing at the USDA-ARS Horticultural Crops Research Laboratory in Corvallis, Oregon, USA, a ‘Glen Clova’ plant that originated in Europe, induced severe symptoms on indicator plants causing mottling, epinasty and apical necrosis. Testing for all Rubus viruses with available laboratory based detection tests failed to identify a known virus in the plant. In an effort to determine the causal agent(s) of the symptoms, dsRNA was extracted from the ‘Glen Clova’ plant and cloned. Sequence analysis revealed the presence of three novel viruses in the plant, temporarily designated as Glen Clova virus -1, -2 and -3 (GC-1, -2, -3). GC-1 is a novel closterovirus with sequence similarity to Citrus tristeza virus, GC-2 is a member of the family Flexiviridae and shares greatest similarity with members of the virus family that infect rosaceous hosts. GC-3, a unique plant virus, belongs to the Dicistroviridae, a family of picorna-like insect viruses and is similar to a virus identified recently in strawberry. RT-PCR based detection protocols have been developed for the three viruses. GC-1 has been identified in several raspberry plants from the state of Washington. One of these plants, a yellow raspberry, did not have any other detectable viruses. When leaves from this plant were used to graft R. occidentalis, a standard indicator for most viruses of Rubus, the plant developed mosaic symptoms but not the tip necrosis and epinasty. Testing of the graft and aphid transmissible virus-like agents of Rubus from the UK is currently underway through a collaborative project with colleagues at SCRI in Invergowrie, Scotland. Also, transmission studies are currently underway.