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Sugarcane streak mosaic virus (SCSMV), a member of the family Potyviridae, is an important viral pathogen affecting sugarcane production in India. The variability in the nucleotide (nt) and amino acid (aa) sequences of helper component proteinase (HC-Pro) of SCSMV isolates from India was investigated and compared with those of previously published virus isolates from different Asian countries. Comparison of all of the sequenced virus isolates revealed a high level of diversity in the HC-Pro gene (72-97% nt sequence identity; 83-99% aa sequence identity), and the Indian isolates were found to be the most divergent (up to 12% variation at the amino acid level). Phylogenetic analysis revealed clustering of 16 SCSMV isolates into two groups. Group I included isolates from India and Pakistan, and group II consisted of isolates from Japan and Indonesia. Recombination analysis revealed nine potentially significant recombination events, and putative recombination sites were identified throughout the HC-Pro gene. Analysis of selection pressure indicated that the HC-Pro gene of SCSMV is under strong negative selection. It is likely that recombination, along with strong negative selection, enhances the speed of elimination of deleterious mutations in the HC-Pro gene.

Sugarcane streak mosaic virus (SCSMV), a member of the genus Poacevirus, family Potyviridae, is an important viral pathogen affecting sugarcane cultivation in India. The complete nucleotide sequence of a SCSMV isolate from India (SCSMV-IND) was determined. The linear, assembled, single-stranded positive-sense RNA genome of SCSMV-IND was 9,786 nucleotides in length (excluding the poly (A) tail) and encoded a polyprotein of 3,131 amino acid residues. The genome of SCSMV-IND shared high degree of sequence identity with SCSMV-PAK (93 % at nucleotide and 97 % at amino acid), and shared only 81 % nucleotide and 94 % amino acid identities with all the four SCSMV isolates (SCSMV-JP1, -JP2, -ID, and -THA). Phylogenetic tree analysis of the complete genome sequences of SCSMV isolates revealed that they can be clustered into two groups. SCSMV-IND and -AP isolates showed 18 % (nucleotide) divergence within the highly conserved 3' partial genome, suggesting a high level of genetic diversity among the Indian SCSMV isolates.

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