First Report of Cucumber mosaic virus in Paeonia lactifera in France.

Chinese peony (Paeonia lactiflora Pall.), a hardy ornamental plant of the family Paeoniaceae cultivated in gardens and for cut flower production, is frequently infected by Tobacco rattle virus (TRV) in the field. The virus usually induces severe mosaic and chlorotic ringspot symptoms in the leaves, decreasing the commercial value of cut flowers. TRV is routinely detected by mechanical inoculation onto Nicotiana tabacum cv Xanthi, where it induces typical necrotic local ringspots in 3 to 7 days, followed by a reverse transcription (RT)-PCR test (2). In 2004, Xanthi test plants inoculated with sap extracts from 4 of 36 P. lactiflora cv. Odile plants grown in a field plot in the region of Hyères (southeast France) showed systemic mosaic symptoms in addition to the TRV-typical response. In each case, Cucumber mosaic virus (CMV) was detected by the reactions of a range of inoculated plants (1), the observation of 30 nm isometric particles in crude leaf extracts with the electron microscope, and by positive reactions in double antibody sandwich (DAS)-ELISAs with specific polyclonal antibodies. In double-immunodiffusion analysis, these isolates were shown to belong to the group II of CMV isolates (3). ELISA of the peony plants confirmed the presence of CMV and revealed two additional infected plants in the spring of 2006. Following isolation from local lesions on Vigna unguiculata and multiplication in Xanthi tobacco plants, one of the isolates was used to inoculate manually or with Myzus persicae aphids 10 CMV-free plants of P. lactiflora cv. Odile obtained from meristem culture. Three months postinoculation, only three of the aphid-inoculated plants were CMV positive by DAS-ELISA. No change was observed at 1 year postinoculation and no symptoms have been observed, even in CMV-infected plants. CMV appears to be latent in P. lactiflora, therefore detection of CMV before vegetative propagation of the plants is advised because of the risks of synergism for symptoms with other viruses such as TRV. To our knowledge this is the first report of CMV in peony. References: (1) L. Cardin et al. Plant Dis. 87:1263, 2003. (2) D. J. Robinson J. Virol. Methods 40:55, 1992. (3) M. J. Roossinck. J. Virol. 76:3382, 2002.