Variability of potato virus Y in potato crops in France

A collection of 332 PVY isolates, originating from potato crops. was charac terized in order to seek the newly described PVY variants, (PVYW)-W-N and P VYZ Serologically, 284 samples were found to contain only PVYO, 36 samples to contain only PVYN, whereas 12 samples were doubly infected by both PVYO and PVYN. All 36 isolates, serologically PVYN-typed and 16 isolates serolog ically PVYO-typed, induced vein necrosis on tobacco. The latter 16 isolates reacted like a Polish standard (PVYW)-W-N isolate and are probably new mem bers of that PVY subgroup; in the panel of samples, they originated from po tato cultivars never previously reported as infected by (PVYW)-W-N and thei r high incidence probably indicates that they are more widespread than comm only accepted. Indexing of 108 PVYO isolates on three potato cultivars (Des iree, Eersteling and Maris Bard) carrying hypersensitivity resistance genes to PVYO, PVYC and PVYZ, respectively, revealed the presence of various pat hotypes. Two isolates reacted as two standard isolates, designated PVYZE, O riginating from Spain and previously suspected to be PVYZ members; these is olates were able to overcome the hypersensitivity genes in the three potato cultivars and consequently were members of a newly recognized pathotype. A nother isolate evoked the reactions expected after infection with PVYZ Surp risingly, PVYC was only found in one sample that was doubly infected by PVY O.