In September 2002, several unthrifty Verbena canadensis ‘Homestead purple’ plants were received at the Division of Plant Industry in Gainesville, FL. Symptoms included very subtle yellowing and distortion or stunting of the younger leaves, symptoms that could be overlooked as a nutritional problem. Symptomatic leaves were ground in phosphate buffer and mechanically inoculated to a variety of plants that included Antirrhinum majus, Chenopodium amaranticolor, Datura stramonium, Gomphrena globosa, Pisum sativum, Trifolium pratense, T. repens, Vicia faba, and Vigna unguiculata. These hosts showed symptoms similar to those described for infection by Clover yellow mosaic virus (ClYMV) (3). In addition, the virus systemically infected Arachis hypogaea, Catharanthus roseus, C. quinoa, Nicotiana benthamiana, and healthy seed-grown Verbena × hybrida. No symptoms were seen in inoculated Zinnia elegans, N. glutinosa, N. clevelandii, Lycopersicon esculentum, Cucumis sativus, or Capsicum annuum. However, back inoculations of Cucumis sativus to C. amaranticolor gave typical local and systemic symptoms. Microscopic examination of leaf strips of infected V. faba revealed banded inclusions typical of the genus Potexvirus (1). Reverse-transcription polymerase chain reaction (RT-PCR) using degenerate primers for the genus Potexvirus (2) produced a 750-bp product that is the expected product for the genus Potexvirus. The RT-PCR product was cloned in pGem-T easy (Promega, Madison, WI) and sequenced. BLAST (http://www.ncbi.nlm.nih.gov/ BLAST/) analysis of the sequence showed an 82% identity at the nucleotide level with the RNA polymerase gene of ClYMV. Leaf extracts of the original verbena, several inoculated hosts, and a known sample of ClYMV in N. benthamiana were tested in sodium dodecyl sulfate immunodiffusion (4) against antiserum to the degraded capsid protein of ClYMV. A reaction of identity was seen with infected samples but not with samples for comparable virus-free plants. To our knowledge, this is the first time this virus has been found in the eastern United States. It is not known how or if the presence of this noninsect transmitted virus in an ornamental will affect the agricultural, forage, or ornamental industries in the east or how widely distributed Verbena sp. infected with this virus may be at this time.
References: (1.) R. G. Christie and J. R. Edwardson. Fla. Agric. Exp. Stn. Monogr. 9, 1994. (2.) A. Gibbs et al. J. Virol. Methods 74:67,1998 (3.) M. J. Pratt. Can. J. Bot. 39:655. 1961. (4) D. E. Purcifull and D. L. Batchelor. Fla. Agric. Ext. Stn. Bull. 788, 1977.