Population structure and diversity of banana bunchy top virus and banana bract mosaic virus.

Abstract

Banana bunchy top virus (BBTV), a type member of the genus Babuvirus of the family Nanoviridae, is a multicomponent single-stranded DNA virus which infects banana and plantain in most parts of the world where it is grown, leading to serious losses in production. It was reported as early as in 1880 in Fiji and later it spread to all the continents except the Americas. Banana bract mosaic virus (BBrMV), a species in the genus Potyvirus (family Potyviridae), is of recent origin in banana. It causes serious losses to the banana in the Philippines and India. It was authentically reported from the Philippines in 1989 and later from India and Sri Lanka. The genetic diversity and population structure of the viruses is very important to develop strategies to design better management options. In cases of multicomponent viruses like BBTV, reassortment, recombination, and mutations are the main mechanisms of genetic changes and evolution, whereas recombination is more common in BBrMV. RNA viruses are known to evolve very quickly owing to their high replication rate, short generation times, and error-prone RNA polymerases which lead to mutations. These genetic variabilities occurring in viruses will be fixed if they are advantageous for the virus to survive and adapt to various conditions. The selection pressure determines the fixation of mutation, recombination, and reassortment in a population. Many systematic studies have been performed on diversity and population structure of BBTV, whereas work on the BBrMV is limited. Based on the studies, the movement of BBTV appears to be neither consistent with the movement of banana across the globe nor with the human-mediated transcontinental spread, but it is relatively through infrequent movement events over the past 300 years from its centers of diversity in India and Southeast Asia (SEA). In this chapter, the genetic diversity of two banana viruses having DNA and RNA genomes—BBTV and BBrMV, respectively—are dealt with in detail. The causes of genetic diversity such as reassortment, recombination, and mutations are discussed for developing effective future management strategies for viruses.