Alfalfa mosaic virus

Alfalfa mosaic virus (AMV) is a virus which infects a wide variety of plant species, many of commercial importance as crops, usually causing a yellow mosaic or mottled pattern on the leaves and necrosis of plant tissues. AMV belongs to class IV of the Baltimore virus classification system, the family Bromoviridae and the genus Alfamovirus, of which it is the only member. AMV may also be known as Lucerne mosaic virus or Potato calico virus.

AMV was first isolated from alfalfa (Medicago sativa) by Weimer in 1931. A large number of plant species from more than nine families have been shown to be susceptible to infection by AMV experimentally. It is transmitted by a number of species of aphid and also from a parent plant to the seed via pollen.

The genome of AMV consists of positive sense, single stranded, RNA. The genome is approximately 8.27kb long in total and is in three segments, designated RNA-1, -2 and -3 which are 3.64kb, 2.59kb and 2.04kb in length respectively. AMV is a multipartite virus which means each of these segments are packaged into separate virion particles and all types of particle need to be present in the same plant cell to cause a successful infection. As well as genomic RNA, some particles contain a sub-genomic mRNA molecule called RNA-4 which is transcribed from a negative sense copy of RNA-3 and encodes the capsid protein.