Transmission Electron Micrograph (TEM) of particles of Tobacco mosaic virus (TMV). Inside the rod, protein molecules are wound helically down the full length of the virus, housing and protecting the nucleic acid of RNA. The effect of TMV infection varies from death of the host plant to severe lesions on the leaf surface. Plant viruses like TMV are transmitted by insects, pests and nematode worms. TMV is a positive-sense single stranded RNA virus, genus tobamovirus that infects a wide range of plants, especially tobacco and other members of the family Solanaceae. The infection causes characteristic patterns, such as mottling and discoloration on the leaves. TMV was the first virus ever to be discovered. Although it was known from the late 19th century that an infectious disease was damaging tobacco crops, it was not until 1930 that the infectious agent was determined to be a virus Magnification: over 44,000x.