1Natural Resources Institute, University of Greenwich, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK.
2Department of Plant Pathology, University of Agricultural Sciences, Bangalore-560065.
Begomoviruses (family Geminiviridae) cause severe diseases of dicotyledonous plants in tropical and sub-tropical regions. Published and our recent data indicate that at least four begomoviruses infect legumes in the Indian sub-continent. The spatial distribution of these viruses has shown that Mungbean yellow mosaic India virus has been found in Pakistan, Bangladesh and North India whereas Mungbean yellow mosaic virus occurs in South India. In contrast, the recently described and host-restricted Dolichos yellow mosaic virus and horse gram yellow mosaic virus have been found both in the North and South India. A similar spatial distribution has also been recorded for tomato-infecting begomoviruses. All these viruses are transmitted by the single species of the whitefly, Bemisia tabaci, which is considered to be a species complex. Based on the mitochondrial cytochrome oxidase I gene sequences, at least three indigenous B. tabaci genotypes and two introduced, B and Q, currently occur in Asia. Whether or not the different indigenous genotypes are adapted to particular host-plants and transmit viruses differentially, which thereby influences the virus’ distribution is not yet understood. Analysis of DNA-A sequences of begomoviruses reveals a fundamental division of the Old World begomoviruses into two clades: one which contains viruses exclusively infecting leguminous plants and the other containing viruses infecting non-leguminous plants. It has been suggested previously that genomic and antigenic variation among begomoviruses is primarily correlated to geography rather than host range. The Old World legume-infecting begomoviruses seem to be an exception to this rule. They represent a distinct lineage of begomoviruses that are distantly related to others from the same geographical area. The probable influences of hosts and vector on the spatial evolution of begomoviruses in the Indian subcontinent will be discussed.
