Arch Virol (1997) 142: 2131±2146
Partial characterization of a new virus from ranunculus with a
divided RNA genome and circular supercoiled thread-like
A. M. Vaira, R. G. Milne, G. P. Accotto, E. Luisoni
, V. Masenga, and V. Lisa
Istituto di Fitovirologia Applicata CNR, Torino, Italy
Accepted July 9, 1997
Summary. An undescribed virus, here named ranunculus white mottle virus,
was isolated in Italy from cultivated ranunculus showing mottle and distortion
of leaves. The virus was mechanically transmissible to several herbaceous
hosts. In negative stain, the particles appeared as circularised supercoiled
threads 3 nm in diameter of different contour lengths; in some conditions the
circles collapsed to form linear pseudobranched structures 9 nm in diameter.
Immunolabeling of thin sections showed that 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 mottle mosaic virus. A major 43 kDa
protein was present in puri®ed preparations and in infected plant tissue, as also
was a minor 28 kDa protein, serologically related to the major one. Nucleic
acids extracted from puri®ed particles consisted of at least three RNAs, of
approximately 7.5, 1.8 and 1.5 kb, which appeared partly in single- and partly in
double-stranded form. Puri®ed preparations, but not viral RNAs, when
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 Bunyaviridae.
Several viruses have been reported in ornamental ranunculus crops: cucumber
mosaic cucumovirus (CMV), tobacco mosaic tobamovirus (TMV), tobacco
necrosis necrovirus (TNV), tobacco rattle tobravirus (TRV), potato Y potyvirus
(PVY), ranunculus mottle potyvirus (RMV), tomato spotted wilt tospovirus
(TSWV) and impatiens necrotic spot tospovirus (INSV) .
* Permanent address: DIVAPRA, Universita
degli Studi di Torino, Torino, Italy.