Abstract
Brown rings on the tuber surface and internal brown arc symptoms were observed on potatoes harvested in November-December of 1980 in Hiroshima Prefecture. A virus isolated from these tubers was identified as potato mop top virus (PMTV) based on host range, symptoms induced, soil-transmissibility, particle morphology, stability in crude sap and serological relationships. PMTV-infected potato “Norin No. 1” grown at a temperature of 15 C showed yellowing or necrosis beside the leaf veins and also necrosis in netted veins. Infected tubers exhibited brown ring symptoms after twice treatments of the storage for 15 days at 18 C and 10 days at 9 C, respectively. The virus infected mechanically 13 plant species in three families (Chenopodiaceae, Aizoaceae and Solanaceae) among 45 species in 11 families. Diagnostic symptoms were produced on inoculated leaves of Chenopodium amaranticolor and Nicotiana debneyi. Soil transmission of the virus was confirmed by two different methods as follows. Potato plants “Norin No. 1” and N. debneyi grown in the soil from the fields infested with PMTV showed characteristic symptoms. N. debneyi plants were also infected through soil when planted in soil where powdery scab-infected plants to which PMTV had been mechanically inoculated were grown. Thermal inactivation point, dilution end point and longevity in vitro of the virus ranged between 65 and 70 C for 10 min, 10-2 and 2×10-3, and 5 and 7 days at 20 C, respectively. The particles were rod-shaped about 20nm in width and exhibited two peaks of 140-150 and 270-300nm in length. Antiserum obtained from rabbit immunized with the injections of the partially purified virus showed a titer of 1, 024 in immuno-electron microscopy tests. The virus also reacted positively with antiserum against PMTV from England.
