Molecular analysis of two complete rice tungro bacilliform virus genomic sequences from India

The complete genomic sequences of two geographically distinct isolates of rice tungro bacilliform virus (RTBV) from India were determined. Both the sequences showed equal divergence from previously reported Southeast Asian isolates. Numerous insertions, deletions and substitutions, mostly in the intergenic regions, were found. The genome sizes were 7907 and 7934 bp respectively, 95 and 68 residues short of an infectious clone reported earlier. Between them, both the isolates showed high homology all along the genome, except for a 30-nucleotide insertion/deletion close to the 3' end of ORF III in one of them. Both the isolates indicated an unconventional start codon in ORF I, similar to the type isolate. In addition, as novel features, both the Indian isolates showed an unconventional start codon for ORF IV. Considering the low amounts of genome variability noticed in other RTBV isolates, the Indian isolates show that they have diverged sufficiently from the rest and should be considered belonging to a distinct strain.