Diversification into the genus Badnavirus: phylogeny and population genetic variability

Badnaviruses (family Caulimoviridae) have semicircular dsDNA genomes encapsidated into bacilliform particles. The genus Badnavirus is the most important due to its high number of species reported infecting cultivated plants worldwide. This study aimed to evaluate the phylogenetic positioning and population genetic variability into Badnavirus. Data sets comprising the badnavirus complete genome and partial sequences of the RT and RNaseH genes were obtained from the GenBank database. Multiple nucleotide sequence alignments from complete genome, ORFIII, complete genomic domain RT/RNaseH (1020pb) and partial (579pb) were performed. A total of 127 genomes were obtained, representing 53 species of badnavirus. Nucleotide sequence comparisons for the RT/RNaseH domain showed only a few isolates reported as distinct species shared ≥80% identity, the current threshold used for species demarcation into this genus. Phylogenetic trees for the complete genome and for ORFIII showed four well supported clusters (badnavirus groups 1-4), with clusters 1 and 3 being sister groups comprising predominantly sugarcane- and banana-infecting species. Non-tree-like evolution analysis evidenced putative recombination events among badnaviruses, and at least 23 independent events were detected. High levels of nucleotide diversity were observed for the partial RT/RNaseH region in isolates of 11 badnavirus species. These results showed that mutation and recombination are important mechanisms that acting on badnavirus diversification.