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First Report of Cucumber mosaic virus and Turnip vein-clearing virus in Dichondra repens in France, Italy, and China

During surveys of Dichondra repens (kidneyweed, family Convolvulaceae) turfs in public gardens of the Franco-Italian Riviera from 1993 to 2003, leaf mosaic and yellow ringspot symptoms have been observed in Antibes, Menton, Nice, and Vallauris (France) and San Remo and La Mortola (Italy). Isolates from these six locations and from two locations in China (Shanghai and Kunming) have revealed the presence of Cucumber mosaic virus (CMV) based on the behavior of a range of manually inoculated plants (1), the observation of 30 nm isometric particles in semipurified extracts of inoculated Nicotiana tabacum ‘Xanthi’ plants with the electron microscope, and positive reactions in double antibody sandwich (DAS)-ELISAs with specific polyclonal antibodies. All isolates were shown to belong to group II of CMV isolates (3) by double-immunodiffusion analysis. CMV was previously identified in D. repens in California in 1972 (4). Following isolation from local lesions on Vigna unguiculata and multiplication in ‘Xanthi’ tobacco plants, two of the isolates were used to inoculate seedlings of D. repens manually or by Aphis gossypii aphids. Two months later, all inoculated plants showed symptoms similar to those previously observed and were positive in DAS-ELISA. In 2000, a D. repens sample collected in Antibes showing similar symptoms as above, induced necrotic local lesions in inoculated ‘Xanthi’ plants in 48 h, followed by systemic mosaic symptoms typical of CMV, therefore revealing the presence of a second virus. That virus was separated from CMV in apical, noninoculated leaves of Chenopodium quinoa and then used to inoculate a range of test plants. It was infectious in most plants of the families Solanaceae (including Cyphomandra betacea) and Brassicaceae, together with in Chenopodium amaranticolor, C. quinoa, Claytonia perfoliata, Convolvulus spp. ‘Belle de jour’, Digitalis purpurea, Gomphrena globosa, Ocimum basilicum, Plantago lanceolata, and Valerianella olitoria. It induced asymptomatic systemic infections in D. repens. Numerous, rod-shaped, 300 nm long particles were observed in sap extracts of infected plants with the electron microscope, suggesting the presence of a tobamovirus. A set of primers polyvalent for tobamoviruses (2) allowed the amplification of a DNA product of approximately 800 bp through reverse transcription-PCR performed with total RNA extracts from inoculated ‘Xanthi’ plants. The DNA product was cloned and sequenced (GenBank Accession No. EU927306) revealing that the virus belonged to a tobamovirus lineage including Ribgrass mosaic virus and viruses infecting cruciferous plants (Turnip vein-clearing virus [TVCV] and Youcai mosaic virus) and was closest to TVCV (95% amino acid identity; GenBank Accession No. NC_001873). To our knowledge, this is the first report of TVCV in D. repens.

References: (1) L. Cardin et al. Plant Dis. 87:200, 2003. (2) A. Gibbs et al. J. Virol. Methods 74:67, 1998. (3) M. J. Roossinck. J. Virol. 76:3382, 2002. (4) L. G. Weathers and D. J. Gumpf. Plant Dis. Rep. 56:27, 1972.