Phylogeographic evolution of plant viruses

Abstract

Viruses, discovered about four decades after the publication Darwin’s treatise ‘The Origin of Species’, are important tools to address the questions related to the evolution of species. Viruses are unlikely to have existed in the pre-cellular environment, as they require the complex host cell system to replicate and are inert outside such cells. Viruses might have coevolved with their natural hosts. Some of the present day viruses could be escaped host genes, as the genome of some of such viruses is found to be integrated with host genome. However, there is no reason to believe similar origin of all viruses. The viruses that might have originated in one group of organism may occur in another group. Some viruses replicate both in plants and insects as their hosts, leaving the question open about their origin. Whatever the origin, biologically, morphologically and molecularly similar viruses seem to have evolved in diverse pathosystems suggesting convergent evolution. High rates of mutations, genomic recombination, intensification of agricultural practices, exchange of germplasm, and human intervention in inadvertently introducing exotic viruses to new environments and host genes for susceptibility have played key roles in the evolution of present day viruses. In this article, we briefly discuss phylogeographic evolution of some of the important plant viruses like badna-, begomo-, poty- and tospoviruses, which have emerged as a severe constraint in improving crop productivity in the tropics and sub-tropics.