Comparison of isolates of Indian citrus ring spot virus and Citrus psorosis virus.
The coat protein gene clones of Citrus psorosis virus (CPV) and Indian citrus ringspot virus (ICRSV) were compared by PCR using gene specific primers. CPV is a multicomponent ssRNA virus with a coat protein of approximately 48 KDa. The single stranded RNA viral genome is contained in short (300-500 nm) and long (1500-2500 nm) filamentous particles that are readily separated by sucrose density gradient centrifugation. The coat protein gene (CP) resides on short particle RNA (top component). RT-PCR assays were developed for the amplification of a 600 bp fragment and the complete CP gene was cloned. The RNA associated with the top component is a negative sense ssRNA. The RNA of the bottom component is not fully characterized, but specific primers designed based on the available sequences from the 3′-end can amplify a fragment. ICRSV has flexuous particles with a modal length of 640×15 nm with clearly visible cross-banding. The genome consists of positive sense ssRNA of ∼7.5 Kb and coat protein of 35 KDa in size. CP is present at the 3′-end of the genome. RT-PCR assays were developed to amplify 500 bp of CP using gene specific primers. The CP gene was cloned in a cloning vector. The failure to amplify the coat protein gene of ICRSV by the specific primers of CPV suggests that these 2 viruses are quite distinct.