Begomovirus

The genus Begomovirus contains more than 100 species and belongs to the taxonomic family Geminiviridae. They are plant viruses that as a group have a very wide host range, infecting dicotyledonous plants. Worldwide they are responsible for a large amount of economic damage to many important crops such as tomatoes, beans, squash, cassava and cotton.

Morphology
Virus particles are non-enveloped. The nucleocaspid is 38nm long and 15-22nm in diameter. While particles have basic isocaherdal symmetry, they consist of two incomplete icosahedra - missing one vertex - joined together. There are 22 capsomeres per nucleocapsid.

Genome
Single stranded closed circular DNA. Most begomoviruses have a bipartite genome:, this means that the genome is segmented into two segments (referred to as DNA A and DNA B) that are packaged into separate particles. Both segments are generally required for successful symptomatic infection in a host cell, but DNA B is dependent for its replication upon DNA A, which can in some begomoviruses apparently cause normnal infectons on its own.

Transmission
The virus is obligately transmitted by an insect vector: this is a whitefly of the species Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). This vector allows rapid and efficient propagation of the virus because it is an indiscriminate feeder.

Disease
The type species Potato yellow mosaic virus (PYMV) is a Begomovirus, first identified in the late 1980s, that causes an infection in tomatoes. Disease is manifested in the infected plant as yellow mosaic or mottling, leaf distortion and crinkling and stunting. In Trinidad this disease in tomato is endemic and causes an estimated yield loss of 50-60%. PYMV disease is also an economical problem in the Caribbean. The type species Bean golden yellow mosaic virus (BGYMV) also belongs to the Begomovirus genus. It causes a serious disease in bean species within Central America, the Caribbean and southern Florida.