Potato Virus M Found in Japan

Abstract

A virus was isolated from apparently healthy plants of potato varieties, USDA seedling 41956 and Kintoki-imo. The virus was transmitted by sap, but not by aphids so far as the present study concerned. By sap inoculation, it produced ring-like local lesions on the inoculated leaves of Nicotiana debneyi, while it caused systemic infection without symptoms in tomato and egg plant. Other plants such as Solanum demissum, S. villosum, Chenopodium amaranticolor, C. capitatum, C. murale, and Gomphrena globosa were also susceptible to the virus. Several potato varieties also became infected systemically.The virus was inactivated in 10 minutes between 65 and 70°C, and between 2 and 3 days, at room temperature (ca. 20°C). Dilution end point was shown to lie between 1:5, 000 and 1:10, 000. In electron microscopy using direct negative staining method devised by Doi et al. (1965), elongated particles of about 650mμ were observed. The virus was identified with potato virus M (PVM), because of its similarity to the description of PVM by Bagnall et al. (1956) in host range, mode of transmission, symptomatology, physical properties, and particle morphology. Antisera against PVM and PVS (potato virus S) were prepared by intravenous injections of rabbits with partially purified virus preparations. The antiserum against PVM was shown to have a homologous titre of 1:256 in precipitation test, and to be applicable to slide flocculation test. Result of cross precipitation tests between PVM-antiserum and PVS, and vice versa, showed some serological relationship between PVM and PVS. In the potato varieties Norin No.1, Oojiro, and Kennebec, mild to severe symptoms were observed on field-grown plants, naturally infected with PVM. The characteristic symptoms associated with PVM were of veinal streak, glossy appearance of leaf surface, crinkling, and downward curling of leaflets. Percentages of infection by PVM in seed potatoes maintained by the Tsumagoi National Potato Foundation Seed Farm were 11% in Norin No.1, 50% in Oojiro, 14% in Kennebec, 31% in Danshaku-imo, and almost 100% in Saco, USDA seedling 41956, and Kintoki-imo variety, respectively. With an exception of Norin No.1, these varieties were often symptomless carriers of PVM under field conditions.