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A New Ilarvirus Isolated from Grapevine in Greece

In 1994, characteristic viruslike symptoms on grapevine were reported in the collection of the Grapevine Institute in Athens, Greece, on the hybrid Baresana × Baresana. The symptoms were sharp angular mosaic, leaf crinkle, and little leaf. The affected vines showed gradual decline and severe stunting or death. Such vines produced abortive flowers or very few berries with smaller, wrinkled, and nongerminating seeds. Serological testing, by enzyme-linked immunosorbent assay (ELISA), of the affected vines against the most common grapevine viruses Alfalfa mosaic, Arabis mosaic, Grapevine fanleaf, Grapevine fleck, Grapevine A, Rasberry ringspot, and grapevine leafroll-associated viruses gave negative results. A virus was isolated from affected grapevine young leaves by mechanical inoculation of Gomphrena globosa and single lesioned. The virus host range included G. globosa (local and systemic dark red or necrotic lesions), Chenopodium quinoa (necrotic local lesions and systemic mottle), and three tobacco cultivars (sharp necrotic local lesions, 1 to 3 mm in diameter). Pollination of C. quinoa with pollen from infected plant gave about 30% infected seedlings. The virus was purified from C. quinoa by differential centrifugation using 0.02 M phosphate buffer pH 8.0, containing 0.01 M DIECA and 0.01 M sodium thioglycolate as extraction buffers. In a purified preparation, quasisphaerical virus particles of about 29 nm were observed. Electrophoretic mobility of the viral coat protein showed a molecular weight of 30 kDa. Using purified preparations, an antiserum was obtained with a titer of 1:1024 in microprecipitin test and an optimum IgG dilution in ELISA of 1:10,000 for maximum absorption at OD_{405 nm} Using degenerate primers designed from homologous regions in RNA-2 corresponding to a fragment of the polymerase gene of Ilarviruses, the expected 381-bp polymerase chain reaction product was obtained. This product was cloned and sequenced. Comparisons with sequence data from the homologous regions of RNA-2 of other known Ilarviruses, showed that the sequence of the above 381-bp amplicon shared 72% sequence similarity with Tobacco streak virus, 67% of Citrus variegation virus and Spinach latent virus, 66% of Asparagus virus 2 and Elm mottle virus, and 65% of Citrus leaf rugose virus. Based on the above data, it is concluded that the isolated virus is an Ilarvirus with closest similarity to Tobacco streak virus. From the relative bibliography (1--3) it appears that the virus reported here is different from Grapevine line pattern virus, a possible Ilarvirus, previously reported from Hungary.

References: (1) J. Lehoczky et al. Kertgazdasag 19:61, 1987. (2) J. Lehoczky et al. Phytoparasitica 17:59, 1989. (3) J. Lehoczky et al. Phytopathol. Medit. 31:115, 1992.