Analysis for effct of the ratios of CMV RNA species on the viral multiplicalion in tobacco tissues

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Mechanism for the suppression of cucumber mosaic virus (CMV) multiplication is analyzed, with special reference to the green island tissue of mosaic leaves and the symptomless leaves periodically appear in the CMV-infected tobacco plants. Tobacco cv. Xanthi nc. was infected with a satellite-free isolate of CMV-pepo and analyzed for the early stage of infection. The symptomless leaves and the green tissue were resistant to the CMV inoculation with virus particles or viral RNA.Those tissues contained double stranded RNA 3 and 4 of the CMV genome. They contained very low level of single stranded RNA of CMV.They contained infectivity and coat protein (CP) as low as 5% of those in the yellow tissue. Ratios for the volume of RNA 3 and 4 to RNA 1 and 2 in the virus particles recovered from the tissues on each leaf position varied along with the symptom types appeared on each leaves. Symptomless leaves appeared above the leaves with larger ratio of RNA 3 and 4 to RNA 1 and 2. Virus multiplication was severely suppressed in the green islands, however, it was recovered in the protoplasts prepared from the green tissue. From these results, resistance in the symptomless leaves or the green tissue is not considered to be caused by CP.Replication of CMV RNA might be specifically suppressed by some unknown mechanism. Larger volume of RNA 3 and 4 may cause to develop the symptomless leaves or the green islands.