Molecular characterization and genetic diversity of Tobacco streak virus infecting soybean (Glycine max L.)

Soybean (Glycine max L.), the most popular oil seed crop, grown in the experimental fields of Tamil Nadu Agricultural University and adjoining areas exhibited symptoms of necrosis and stunting. The symptoms were similar to bud blight of soybean caused by the Tobacco streak virus (TSV) and the disease is most prevalent throughout the country. To study the nature of infection, sap inoculation of the soybean strain induced local as well systemic infection on cowpea plants cv. C 152 and resulted in the production of circular necrotic lesions and death of plants. The samples were also serologically positive in DAC-ELISA and it has also yielded a protein band of approximately 29 kDa corresponding to coat protein of TSV in Western blot assay. For the characterization of virus, RT-PCR was carried out with a newly designed coat protein gene specific primer, which resulted in amplification of the expected 929 bp size. Sequence analysis of the CP gene had nucleotide similarity of 80.6 to 99.3% with known isolates of TSV. The multiple sequence alignment revealed that CP gene showed single unique variation and some of deletion and addition mutation was found in nucleotide and amino acid sequences against the isolates of other soybean Brazil and USA isolates and produced single unique variation at position 344 where adenine was substituted with guanine. There was no deletion and addition between nucleotide sequences in the group of Indian isolates, further confirms the placement of the soybean isolate of TSV in a single subgroup.