RFLP MAPPING OF THE WHOLE GENOME OF 10 VIRAL ISOLATES REPRESENTATIVE OF DIFFERENT BIOLOGICAL GROUPS OF POTATO-VIRUS-Y

Ten PVY isolates representative of four PVY groups (Y-N, Y-NTN, Y-N-W, Y-O), differing by their ability to induce reactions of vein necrosis on tobacco and tuber necrosis on potato, were studied in order to res earch the regions of the viral genome involved in these necrosis pheno mena. The whole genome of these isolates was amplified in two fragment s (4 063 and 5 670 nucleotides) and was subjected to a restriction fra gment length polymorphism (RFLP) study. In the first 4 063 nucleotides of the PVY genome, a phenetic analysis of RFLP data resulted in a clu stering of our PVY isolates into three groups: PVYN isolates (group A) ; PVYNTN and PVYN-W isolates (group B) and PVYO isolates (group C). In the last 5 670 nucleotides, two groups were found: PVYN and PVYNTN is olates (group D) and PVYO and PVYN-W isolates (group E). From this clu stering and the necrosing properties known for these isolates, the tob acco necrosis determinants seem more likely located in the 5' than in the 3' half part of the viral RNA, whereas it would be the opposite si tuation for the determinants of the necrosis on potato tubers. Moreove r a recombination event seemed to have occurred in the genome of the P VYN-W isolates.