Sequence variability in the coat protein gene of two groups of banana bunchy top isolates

Complete nucleotide sequences of the coat protein gene (DNA-3) of banana bunchy top virus (BBTV) were obtained from five geographical isolates by PCR. Analysis of these sequences revealed two distinct groups of BBTV isolates with those from the Philippines, Taiwan and Vietnam forming the Asian group while the South Pacific/African group consisted of isolates from Australia, Burundi and Fiji. At the nucleotide level, the sequences of DNA-3 were more similar between isolates from the same group (maximum 5.86%) than between members of the two different groups (maximum 13.05%). At the amino acid level, the BBTV coat protein remained highly conserved, with a maximum of < 3% sequence variation between all isolates in this study. There was a significantly higher degree of divergence between the Asian isolates, which may indicate that BBTV has been present in this region for an extended period of time or that there have been multiple introductions of BBTV into bananas. The high level of conservation in the BBTV coat protein suggests that any of the DNA-3 sequences presented in this study would probably be equally effective as transgene in attempts to generate transgenic banana plants with resistance to both groups of BBTV isolates.