PARTIAL CHARACTERIZATION OF A NEW VIRUS FROM RANUNCULUS WITH A DIVIDED RNA GENOME AND CIRCULAR SUPERCOILED THREAD-LIKE PARTICLES

An undescribed virus, here named ranunculus white mottle virus, was is olated in Italy from cultivated ranunculus showing mottle and distorti on of leaves. The virus was mechanically transmissible to several herb aceous hosts. In negative stain, the particles appeared as circularise d supercoiled threads 3 nm in diameter of different contour lengths; i n some conditions the circles collapsed to form linear pseudobranched structures 9 nm in diameter. Immunolabeling of thin sections showed th at viral antigen was widely distributed in the cytoplasm of parenchyma cells. The virus was not serologically related to the morphologically similar tenuiviruses, citrus psorosis-ringspot virus and tulip mild m ottle mosaic virus. A major 43 kDa protein was present in purified pre parations and in infected plant tissue, as also was a minor 28 kDa pro tein, serologically related to the major one. Nucleic acids extracted from purified particles consisted of at least three RNAs, of approxima tely 7.5, 1.8 and 1.5 kb, which appeared partly in single-and partly i n double-stranded form. Purified preparations, but not viral RNAs, whe n mechanically inoculated, were infectious. Host range, tissue tropism , particle morphology and coat protein size place the virus closest to citrus psorosis-ringspot and tulip mild mottle mosaic viruses. These three viruses in turn show similarities with the Tenuiviruses and Buny aviridae.