Tobamovirus

Tobamovirus is a genus of positive-strand RNA viruses in the family Virgaviridae, named for the host and symptoms of the first virus discovered in it, Tobacco mosaic virus. Many plants, among them tobacco, potato, tomato and squash, serve as natural hosts, and the diseases associated with the genus include necrotic lesions on leaves. The virions are non-enveloped rods with helical symmetry, about 18 nm across and 300 to 310 nm long. The linear, non-segmented RNA genome runs to roughly 6.3 to 6.5 kilobases and encodes at least four polypeptides: replication proteins including an RNA-dependent RNA polymerase, a movement protein that lets the virus pass between plant cells, and a coat protein. Replication is cytoplasmic and transmission is mechanical. The genus is informally divided into four subgroups by the plants they infect (brassicas, cucurbits, malvaceous plants and solanaceous plants) and currently holds 37 recognised species.