First Report of the Natural Infection of Coreopsis auriculata 'Nana' with Lettuce mosaic virus in the United States.

Perennial cultivars of Coreopsis, a genus native to the United States, are widely grown for aesthetics in home gardens and roadsides and are increasingly used in conservation projects and native-plant gardens. During the spring and summer of 2006 and 2007, Coreopsis auriculata 'Nana' plants with foliar symptoms showing chlorotic spots and rings were observed in wholesale and retail nurseries in Washington. Nicotiana benthamiana plants inoculated with crude sap extracts from symptomatic leaves of C. auriculata 'Nana' obtained from two different sources showed systemic mosaic mottling symptoms, indicating the presence of a virus. Symptomatic leaf samples from C. auriculata 'Nana' and N. benthamiana tested positive in antigen-coated plate-ELISA with potyvirus group-specific monoclonal antibodies (Agdia Inc., Elkhart, IN). Additional analysis by ELISA was positive for Lettuce mosaic virus (LMV; Agdia Inc.). To confirm these results, total RNA extracted from symptomatic N. benthamiana leaves was subjected to reverse transcription (RT)-PCR using potyvirus degenerate primers (PNIbF5: 5'-GCCAGCCCTCCACCGTNGTNGAYAA-3' and PCPR1: 5'-GGGGAGGTGCCGTTCTCDATRCACCA-3') covering the 3' end of the NIb gene and the 5' end of the CP gene (1). A single DNA band of approximately 1,000 bp amplified from symptomatic leaves of two independent plants was cloned separately into pCR2.1 (Invitrogen Corp., Carlsbad, CA). Two independent clones per amplicon were sequenced from both orientations. Pairwise comparison of these sequences with corresponding nucleotide sequences of potyviruses in GenBank showed 93 to 99% identity in the NIb/CP region with LMV sequences from France (GenBank Accession Nos. X97704, X65652, and X97705), China (GenBank Accession Nos. AJ306288 and AJ488153), and Brazil (GenBank Accession No. AJ278854). These results confirmed the presence of LMV in symptomatic leaves of N. benthamiana and C. auriculata 'Nana'. The occurrence of LMV has been reported in ornamental plants that included freeway daisy (Osteospermum fruticosum), lisianthus (Eustoma grandiflorum), and gazanias (Gazania spp.) (2-4). To our knowledge, this is the first documented evidence for the occurrence of LMV in Coreopsis, an economically important perennial ornamental widely grown in the United States. Although the origin of LMV in C. auriculata 'Nana' is not known, distribution of cuttings from LMV-infected C. auriculata 'Nana' plants to wholesale and retailers within Washington and across the country by movement of plant material could pose a risk to other ornamentals and crops like lettuce because of the broad host range of LMV and its potential transmission by several species of polyphagous aphids. Seed transmission as a potential means of dissemination of LMV in Coreopsis has not been examined, although the virus is seedborne in other plants such as lettuce. References: (1) Y.-C. Hsu et al. J. Virol. Methods 128:54, 2005. (2) V. Lisa et al. Inf. Fitopatol. 3:58, 1995. (3). D. C. Opgenorth et al Plant Dis. 75:751, 1991. (4) F. M. Zerbini et al. Plant Dis. 81:641, 1997.