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First Report on Tobacco mild green mosaic virus in Calibrachoa Plants (Calibrachoa × hybrida) in Mississippi

Six calibrachoa plants displaying reduced growth, general chlorosis, and blistering on the foliage were purchased from a retail store in Starkville, MS in 2007 and tested for possible virus infections. Transmission electron microscope observations of leaf-dip preparations revealed the presence of rigid rod virions reminiscent of tobamoviruses in all samples. The virus was easily mechanically transmissible and induced systemic mosaic/mottling/necrosis symptoms in inoculated Nicotiana benthamiana, N. tabacum cvs. Xanthi and Turkish, N. rustica, N. clevelandii, and N. glutinosa plants as well as in pepper (Capsicum annuum cv. Sweet banana). In double antibody sandwich (DAS)-ELISA tests, the virus reacted slightly with antibodies to Tobacco mosaic virus and Tomato mosaic virus (Agdia Inc, Elkhart, IN) indicating a serological relationship with these two viruses. Final identification of the virus was done by cloning and sequencing a 450-bp-long portion of the viral genome spanning the carboxy terminus of the viral coat protein and 3′ noncoding region from one of the original sources. Analyses showed that the virus in diseased calibrachoas is an isolate of Tobacco mild green mosaic virus (TMGMV) and shared 96 to 97% nucleotide identity with sequences of TMGMVCPR-18 (1) (Accession No. AF132908) and several other isolates of this virus available in GenBank. Furthermore, TMGMV was ascertained in all six calibrachoa in reverse transcription-PCR tests using virus-specific primers designed on the generated genomic region. To our knowledge, TMGMV has not been previously reported from calibrachoa plants or from Mississippi in general. In addition, our results stress the importance of the retail industry in the dissemination of viruses on the regional/national scale.

Reference: (1) S. Bodaghi et al. J. Gen. Virol. 81:577, 2000.