Tobacco veinal necrosis determinants are unlikely to be located within the 5' and 3' terminal sequences of the potato virus Y genome

Three potato virus Y isolates, representatives of distinct PVY groups, identified in potato fields in northern Poland were submitted to biological and molecular analysis. Phenotypically, two isolates, PVY(N)-Ny and PVY(N)-Wi, belong to the necrotic strain and the third one (PVY(O)-LW) to the common strain. PVY(N)-Wi, however, did not react with monoclonal antibodies directed against the necrotic strain isolates which recognise PVY(N)-Ny. To characterise the isolates, coat protein genes were sequenced and compared with sequences from databases. The necrotic PVY(N)-Wi isolate showed 99% amino acid homology with the common one-PVY(O)-LW and significantly differed from the second necrotic isolate (PVY(N)-Ny). Sequence based homology matrix and phylogenetic analysis lead to classification of PVY(N)-Ny into group I, encompassing solely necrotic strain isolates, whereas PVY(N)-Wi falls into a phenotypically heterogeneous group II. The sequence analysis allowed for identification of putative group I-specific epitopes. 3'NTR (non-translated region) sequences were identical for PVY(N)-Wi and PVY(O)-LW. The 5'NTR, P1 gene, coat protein gene and 3'NTR sequences of the common (PVY(O)-LW) and the necrotic (PVY(N)-Wi) isolates are 99-100% homologous. This suggests that tobacco veinal necrosis determinants are located outside the 3' and 5' terminal sequences of the PVY genome.