TOBACCO VENOUS NECROSIS DETERMINANTS ARE UNLIKELY TO BE LOCATED WITHIN THE 5'-TERMINAL 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 biol ogical and molecular analysis. Phenotypically, two isolates, PVYN-Ny a nd PVYN-Wi, belong to the necrotic strain and the third one (PVYO-LW) to the common strain. PVYN-Wi, however, did not react with monoclonal antibodies directed against the necrotic strain isolates which recogni se PVYN-Ny. To characterise the isolates, coat protein genes were sequ enced and compared with sequences from databases. The necrotic PVYN-Wi isolate showed 99% amino acid homology with the common one-PVYO-LW an d significantly differed from the second necrotic isolate (PVYN-Ny). S equence based homology matrix and phylogenetic analysis lead to classi fication of PVYN-Ny into group I, encompassing solely necrotic strain isolates, whereas PVYN-Wi falls into a phenotypically heterogeneous gr oup II. The sequence analysis allowed for identification of putative g roup I-specific epitopes. 3'NTR (non-translated region) sequences were identical for PVYN-Wi and PVYO-LW. The 5'NTR, P1 gene, coat protein g ene and 3'NTR sequences of the common (PVYO-LW) and the necrotic (PVYN -Wi) isolates are 99-100% homologous. This suggests that tobacco veina l necrosis determinants are located outside the 3' and 5' terminal seq uences of the PVY genome.