First Report of Tobacco streak virus on Dahlia in the Czech Republic.

Dahlia is an important ornamental crop in the Czech Republic where they have been grown for more than 150 years. New dahlia cultivars have been selected by Czech plant breeders. Virus diseases, including mosaic and stunt caused mostly by Dahlia mosaic virus, have been a problem. From 2003 to 2005, color breaking was observed in several dahlia cultivars of foreign and Czech origin. White stripes in blossoms were most frequently expressed in the second half of the flowering season. No symptoms are visible in flowers of white and yellow cultivars. It was difficult to characterize symptoms on leaves because most cultivars were infected simultaneously by Dahlia mosaic virus. Sap inoculations of Chenopodium quinoa produced local lesions after 5 to 7 days, followed by systemic chlorosis, necrosis of younger leaves, and death of the shoot apex, indicating possible Tobacco streak virus (TSV) infection (2). Spherical particles (25 to 30 nm) were observed in leaf-dip preparations of samples from experimentally infected C. quinoa plants and analyzed by using transmission electron microscopy. These particles became decorated when using immunoelectron microscopy with TSV IgG (Bioreba, Reinach, Switzerland and Neogen, Ayrshire, Scotland). Samples of 80 dahlia cultivars were tested for TSV infection by ELISA using commercially available kits (Bioreba and Neogen). Most of the samples were grown in a collection of dahlia cultivars of Czech and foreign origin and some were obtained from growers in the Czech Republic. Fifty six dahlia cultivars were shown to be TSV infected. ELISA also indicated a higher concentration of the virus in flowers. The identity of the virus isolated from symptomatic plants was confirmed by reverse transcription (RT)-PCR using total RNA extraction from symptomatic plants. RT-PCR (4), using a primer pair (1) derived from the coat protein gene sequence of TSV (3), was followed by electrophoresis on 1.0% agarose gels. Products of the predicted size (approximately 700 bp) were found in naturally infected dahlia plants (n = 10), systemically infected host plants C. quinoa (n = 10), and symptomatic Nicotina megalosiphon (n = 10) that scored as TSV positive by ELISA. No bands of this size were seen in negative controls. To our knowledge, this is the first detection of TSV in the Czech Republic. References: (1) A. I. Bhat et al. Arch. Virol. 147:651, 2002. (2) A. A. Brunt Plant Pathol. 17:119, 1968. (3) B. J. C. Cornelissen et al. Nucleic Acids Res.12:2427, 1984. (4) S. S. Pappu et al. J. Virol. Methods 4:9, 1993.