Virion protein sequence variation among Australian isolates of turnip yellow mosaic tymovirus.

The virion protein genes, and 3' untranslated regions, of six variants of turnip yellow mosaic tymovirus (TYMV) that produced different symptoms in their native host Cardamine robusta and in Chinese cabbage plants, have been sequenced. The sequences have been compared with each other, and with the same region of the pBL-16 clone of the Blue Lake isolate of TYMV. The sequences of the virion protein genes differed by a mean of 1.89% (range 0-2.82%), and the encoded proteins by a mean of 1.71% (range 0-3.17%). The nucleotide differences were confined to the 5'-most 60% of the gene, whereas there were amino acid differences only among residues 12 to 29 and residue 102 (numbered from the N-terminus) of the virion protein involving only hydrophobic residues at the surface of the protein. The amino acid and nucleotide differences between the seven isolates did not correlate with differences in the symptoms they caused, but confirmed earlier estimates of genetic variability in the wild populations of the virus.