Virusrs differ in the number of plant species that they can infect systemically. Some viruses have wide host ranges; cucumber mosaic virus has been reported to infect more than 800 species in 85 families.
Some viruses are restricted to one plant organ, necroviruses are usually restricted to the roots, Iuteoviruses are usually restricted to the phloem cells in the vascular bundle.
The tobacco mosaic-virus(TMV), for example,multiplies within Nicotiana-species,several other solanaceous plants and a few species of other plant families. The name of a virus is usually derived from the name of main host plant.