The complete genome sequence of the Tanzanian strain of Cassava brown streak virus and comparison with the Ugandan strain sequence

The complete genome sequence for an isolate of the Ugandan and Tanzanian strain types of Cassava brown streak virus have been determined using the novel approach of non-directed next generation sequencing. Comparison of the genome sequences revealed that CBSV is highly heterogeneous at the isolate level as well as the strain level. The isolate of the Ugandan strain was found to have a genome 9,070 nucleotides long coding for a polypeptide with 2,902 amino acid residues. The isolate of the Tanzanian strain was 9,008 nucleotides long and coded for a polypeptide with 2,916 amino acid residues. Nucleotide identity between the isolates across the genome was 76%, with protein encoding regions 57-77% and individual proteins had 65-91% amino acid similarity. In addition between the two strains four protein products (PIPO, CI, NIa-Vpg and coat protein) varied in size and an unusual HAM1-like protein, whilst of identical nucleotide length, was found to have the lowest homology. The implication of diversity of CBSV is discussed in the context of speciation, evolution, development of diagnostics, and breeding for resistance.