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First Report of Alfalfa mosaic virus on Rhamnus alaternus in France

Rhamnus alaternus L. (evergreen buckthorn), family Rhamnaceae, is a small, hardy shrub from Mediterranean regions grown for its ornamental persistent green or variegated foliage. Chlorotic oak leaf or ringspot symptoms on R. alaternus leaves have been observed in southern France (Bellegarde, Gard department in 1998; Fanjaux, Aude department in 2000; and Saint-Jean-Cap-Ferrat, Alpes-Maritimes department in 2002). Samples from these three localities revealed the presence of Alfalfa mosaic virus (AMV) due to (i) the symptoms observed in an inoculated diagnostic host range previously described (1), (ii) observation of typical bullet-shaped virion particles of different sizes with transmission electron microscopy, (iii) nonpersistent transmission to Nicotiana tabacum cv. Xanthi-nc by Myzus persicae, and (iv) positive reaction in double-antibody sandwich-enzyme-linked immunosorbent assays (DAS-ELISA) to antibodies raised against AMV (gift of G. Marchoux). In addition, in Fanjaux, Viburnum tinus L. plants located close to the infected R. alaternus plants were also infected by AMV and exhibited typical intense calico mosaics (3). The close species, R. frangula L., was previously identified as a natural host for AMV in Italy (2). Following isolation from local lesions on Vigna unguiculata, the Fanjaux isolate was grown in cv. Xanthi-nc plants, where it induced a severe mosaic and stunting of the plants, and inoculated to 2-year-old virus-free R. alaternus plants either mechanically or with M. persicae (10 plants each). Plants were subsequently kept in an insect-proof greenhouse. At 8 and 12 months postinoculation, only one aphid-inoculated plant showed symptoms on young leaves and was AMV-positive in DAS-ELISA, while no mechanically infected plants were infected. This low infection level together with the rare observation of symptoms in natural conditions suggest that R. alaternus is not frequently infected by AMV.

References: (1) L. Cardin and B. Moury. Plant Dis. 84:594, 2000. (2) F. Marani and L. Giunchedi. Acta Hortic. 59:97, 1976. (3) N. Plese and D. Milicic. Phytopathol. Z. 72:219, 1971.