Abstract
Biological properties of potato virus Y-ordinary strain (PVY-O isolate) and necrotic strain (PVY-T isolate) isolated from potatoes in Japan were compared. PVY-O did not produce necrotic symptoms on Nicotiana tabacum, but produced necrotic local lesions on Chenopodium amaranticolor and C. quinoa. On the other hand, PVY-T produced necrotic flecks and veinal necrosis symptoms on N. tabacum, but did not infect C. amaranticolor and C. quinoa. The use of monoclonal antibodies specific to PVY-O and PVY-T indicated that both strains were not mixed-infected in inoculated plants respectively each other. The nucleotide sequences of the coat protein gene of these two strains were determined. Numbers of nucleotides encoding coat protein of both PVY-O and PVY-T were 801, and numbers of predicted amino acids were 267. Percentage amino acid sequence homology between PVY-O and PVY-T was 91.4%. In comparing the amino acid sequence between PVY-T and other PVY belonging to necrotic strains previously reported in Japan and foreign countries, homology of PVY-TH isolated in Japan and that to PVYN (N) isolated in the Netherlands was 98.5%, but homology to PVYn (F) isolated in France was 93.3%. Amino acid sequence of the N-terminal regions of coat protein varied in sequence in PVY isolates (strains) whereas the C-terminal were highly homologous. Furthermore, amino acid sequences which could discriminate an ordinary strain from a necrotic strain were not found.
