Molecular diagnosis of ranunculus white mottle virus in two ornamental species.

Ranunculus white mottle virus (RWMV), genus Ophiovirus, a possibly tripartite RNA virus, has been reported in commercial Ranunculus hyb. crops since 1990, in North-West Italy, with uncertain pathogenic impact as it was always found in mixed infection with the most common viruses infecting ranunculus and with a low incidence. Cloning of RWMV isolate Rn3 produced several clones targeting RNAs 1 and 2. Two clones were used to obtain non-radioactive probes. In Northern blot experiments with total RNAs from infected plants, probe RW35 recognized RNA 2 while probe RW380 recognized RNA 1. Probe RW35 was chosen as a diagnostic tool. Tissue-print experiments were performed with indicator plants mechanically inoculated with RWMV and showed sensitive detection of the virus. Ranunculus plants, mechanically inoculated with various isolates of RWMV, were tested for infection by stem-squash, and the results were equally reliable. Recently, RWMV was also detected in field plants of anemone hybrids by Northern blotting of total RNA.