Figure 5
Pathogen Biology
ClassificationRaspberry bushy dwarf virus has a unique genome organization
among
plant viruses and has therefore been classified in its own viral genus Idaeovirus. The name Idaeovirus comes from the scientific name for red raspberry, Rubus idaeus.
Genomic Organization
RBDV has a two-part (bipartite) genome that is packaged into 33 nm isometric particles (Fig. 5). The virus contains three RNA species (Fig. 6): RNA 1 (5.5 Kb), RNA 2 (2.2 Kb) and RNA 3 (1.0 Kb). RNA 1 contains one gene or open reading frame (ORF) that encodes the REPLICASE, which is used to copy the viral RNA to make complementary RNA, which in turn serves as a template for the new viral RNA. RNA 2 contains 2 ORFs; the first encodes the viral movement protein which facilitates cell to cell movement of virus by modifying pore size of plasmodesmata and the second contains the information for the viral coat protein. The gene for the viral coat protein is first produced on a small (subgenomic) RNA (RNA 3) from RNA2 and is then used to produce the coat protein which makes the protein shell that protects the viral RNA.
RBDV Strains
There are three reported strains of RBDV: the common or type strain (S), the resistance breaking strain (RB) and the black raspberry strain (B). The type and RB strains are serologically indistinguishable (can not be distinguished by polyclonal or monoclonal antibodies produced to the two strains), but the RB strain can infect all raspberry cultivars while the type strain is unable to overcome the resistance conferred by the Bu gene present in some cultivars. The RBDV type strain is found worldwide but the RB strain has only been reported in Europe. The black raspberry strain is serologically distinct from the other two and has only been found in North America.