Characterization of tobacco mosaic virus isolated from tomato in India

Abstract

Tomato mosaic tobamovirus (ToMV) differs from the type strain of tobacco mosaic virus (TMV) in producing local lesions instead of systemic infection on Nicotiana sylvestris. An isolate collected from Kolar district of Karnataka which produced this differential host reaction was propagated in the greenhouse on N. tabacum cv. Samsun and purified. The virus is a rigid rod shaped particle with a coat protein of molecular weight 18 kDa and genomic RNA of size 6.3 kb. A cDNA library was constructed using a specific primer designed based on the conserved nucleotide sequence at the 3' non coding region of tobamoviruses. The cDNA library was screened for recombinant clones and the recombinant clone 82 with an insert of size 1.04 kb was sequenced in both directions. This sequence was compared with the genomic sequence of TMV and ToMV which showed 93.1 and 73.7 per cent identity, respectively. The sequence encompassed the 3' non coding region, the complete coat protein ORF and 467 nucleotides of the movement protein. The deduced amino acid sequence of the coat protein was compared with that of TMV and ToMV. This sequence was nearly identical to TMV with nine amino acid changes whereas thirty-two changes were observed with ToMV. This suggests that the virus under study is a strain of TMV and therefore we have named it as tobacco mosaic virus tomato strain from Karnataka, India (TMV(Tom-K)).