Biology of a new virus isolated from Lupinus nootkatensis plants in Alaska

Abstract

A new virus named Nootka lupine vein‐clearing virus (NLVCV) was isolated from Lupinus nootkatensis plants that were confined to a relatively small area in the Talkeetna mountains of south‐central Alaska. Annual surveys (2000–03) consistently found leaf symptoms of pronounced vein clearing and mosaic on 3‐ to 4‐week‐old plants in late June. Spherical particles ≈30 nm in diameter were isolated from these leaves. Virions contained a single‐stranded RNA of ≈4·0–4·2 kb and one species of capsid protein estimated to be ≈40 kDa. The double‐stranded RNA profile from naturally infected leaves consisted of three major bands ≈4·2, 1·9 and 1·5 kbp. Protein extractions from either sap or virions of diseased plants reacted to polyclonal antiserum made against the virions in Western blot assays. A predicted PCR product ≈500 bp was synthesized from virion RNA using primers specific to the carmovirus RNA‐dependent RNA polymerase (RDRP) gene. The nucleotide sequence of the amplified DNA did not match any known virus, but contained short regions of identity to several carmoviruses. Only species belonging to the Fabaceae were susceptible to NLVCV by mechanical inoculation. Based on dsRNA profile, size of virion RNA genome and capsid protein, and similarity of the RDRP gene to that of other carmoviruses, it is suggested that NLVCV is a member of the family Tombusviridae, and tentatively of the genus Carmovirus. As the host range, RDRP gene and dsRNA profile of NLVCV are different from those of known viruses, this is a newly described plant virus.