First Report of Calibrachoa mottle virus Infecting Petunia

Calibrachoa mottle virus (CbMV), a tentative carmovirus, was first isolated and reported by Liu et al. (1) from infected Calibrachoa plants. During the spring of 2003, petunia samples from Florida and California sent to testing services at Agdia, Inc (Elkhart IN) tested positive for CbMV by enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassay (ImmunoStrips). These samples also tested positive by carmovirus group-specific polymerase chain reaction (PCR) primers and by immunocapture PCR (2). RNA extracted from these samples with the RNeasy Plant Kit (Qiagen Inc., Valencia, CA) hybridized with a digoxigenin labeled probe derived from purified CbMV viral RNA. All plant samples that tested positive for CbMV were symptomless except one symptomatic sample that also tested positive for Tobacco mosaic virus. From samples that tested positive for CbMV only, mechanical inoculations were made to Chenopodium quinoa at a USDA-ARS greenhouse in Salinas, CA. Representative single, local lesions were used to inoculate additional C. quinoa plants. The resulting local lesions from these inoculations were freeze-dried and further used as virus inoculum (CbMV petunia). Similar inoculum was made with CbMV isolated from Calibrachoa plants (CbMV calibrachoa). Virus-free Petunia hybrida cultivars Surfinia 'Baby Pink' and Surfinia 'Violet' (Jackson and Perkins Inc., Somis, CA) were mechanically inoculated with CbMV petunia and CbMV calibrachoa. Four weeks postinoculation, all plants were tested using ELISA for the presence of CbMV. In greenhouse conditions, 14.3% of 'Baby Pink' plants were positive for CbMV petunia, whereas none were positive for CbMV calibrachoa. 'Violet' plants were 64.3 and 33.3% positive for CbMV petunia and CbMV calibrachoa, respectively. None of the positive plants expressed virus-like symptoms. Virus particles resembling those of CbMV were observed from infected petunia plants with transmission electron microscopy in leaf-dip preparations. To our knowledge, this is the first report of CbMV infecting petunia. Commercial reproduction of petunia plants and maintenance of genetic mother stock are usually by vegetative propagation. CbMV can be transmitted mechanically and is readily propagated along with its host. To produce healthy petunia plants, virus-free mother stock should be used, which requires regular screening of mother stock for CbMV. Reference: (1) H.-Y. Liu et al. Plant Dis. 87:167, 2003. (2) A. M. Harness et al. (Abstr.) Phytopathology 92:S34, 2002.