Indian citrus ringspot virus: a proposed new species with some affinities to potex-, carla-, fovea- and allexiviruses

An isolate of Indian citrus ringspot virus from Kinnow mandarin in northern India had flexuous particles with evident cross-banding and a modal length of 650 nm. It was mechanically transmitted to five herbaceous hosts includ ing Phaseolus vulgaris cv Saxa, in which it became systemic. In thin sectio ns, virus particles were observed in the cytoplasm of parenchyma cells but no specific inclusions were seen. The virus was purified from infected Saxa bean leaves and an antiserum prepared. There was no serological cross-reac tion with representative allexi-, capillo-, potex- and trichoviruses, excep t a faint one-way reaction with Potato virus X. Purified virus yielded a ma jor band, the presumed coat protein (CP), of about 34 kDa, and a single ssR NA of about 7.5 kb, which was infectious. Two ORFs encoding putative protei ns of 34 kDa and 23 kDa were located in the 3' part of the RNA. The product of the 34 kDa ORF was confirmed as the CP by expression in E. coli. The de rived amino acid sequence of the CP contained some short motifs similar to those of potex-, fovea-, carla- and allexiviruses but otherwise there was n o strong similarity to any of these. The 23 kDa ORF contained a zinc finger -like sequence, as in similar ORFs in carla- and allexiviruses but overall amino acid homology with these was low. The virus does not appear to fall i nto any known genus. A new species is proposed. Serological and molecular d iagnostic reagents were prepared.