Molecular characterisation of banana bunchy top virus (BBTV) from Pakistan.

Banana bunchy top disease is caused by a single-stranded circular DNA virus, banana bunchy top virus (BBTV), which is a member of the genus Babuvirus (family Nanoviridae). We have cloned and sequenced five components (DNA-R, DNA-S, DNA-N, DNA-M and DNA-C) of a BBTV isolate originating from Pakistan. In addition, the DNA-R and several other components of five further isolates, originating from geographically distinct sites across the banana-growing area of Sindh province, Pakistan, were cloned and sequenced. Analysis of the sequences indicates that BBTV present in Pakistan belongs to the "South Pacific" group of isolates and that the genetic diversity of the virus in the country is very low. The virus shows the highest levels of sequence identity to BBTV isolates originating from Egypt, India and Australia. The significance of these results with respect to the possible origin of the virus in Pakistan and the prospects for obtaining genetically engineered resistance to the virus are discussed.