Tobacco mosaic virus. Coloured transmission electron micrograph (TEM) of virus particles (virions) of the tobacco mosaic virus (TMV). This plant virus is a tobamovirus, and has an RNA (ribonucleic acid) genome. It was first identified in 1886 in the tobacco plant (Nicotiana tabacum), one of the world's major cash crops. This virus also infects many other plant species. Symptoms are mosaic patterns on the leaves and severe crop loss. The virus is transmitted by seeds (but not pollen) and contact between plants. Magnification: x125,000 when printed 10 centimetres tall.