Tobacco mild green mosaic virus in Impatiens and Osteospermum: new hosts and first report in the UK



In May 2007 two samples of impatiens (Impatiens sp.) (cv. Timor and Totoya) exhibiting possible virus symptoms were received from a nursery in the south of England. Symptoms included stunting, distorted leaves, necrotic lesions and a paler flower colour. ELISA tests for Cucumber mosaic virus, Impatiens necrotic spot virus and Tomato spotted wilt virus were negative. Mechanical inoculation onto indicator plants produced symptoms on Chenopodium quinoa (local chlorotic lesions), Nicotiana benthaniana, N. hesperis and N. occidentalis P1 (all systemic necrosis). Examination of these indicator plants and the original samples by electron microscopy revealed straight rod-shaped particles (approximately 300 nm in length). This strongly suggested the presence of a tobamovirus. Therefore, the samples were tested using a tobamovirus PCR (Agdia) and bands of the correct size (400 bp) were detected. The products were cloned and sequenced (GenBank Accession No. GU77405) and the virus identified as Tobacco mild green mosaic virus (TMGMV).

Following this finding of TMGMV in impatiens, a sample of osteospermum (Osteospermum sp.) (cv. Sheila) was received in March 2008 from a second nursery in the south of England. The sample had leaf symptoms including chlorotic spots and rings. Testing by ELISA was negative for several common viruses including Cucumber mosaic virus, Impatiens necrotic spot virus, Lettuce mosaic virus and Tomato spotted wilt virus. The same virus symptoms as observed for the impatiens samples were detected on indicator plants following mechanical inoculation; examination by transmission electron microscopy revealed suspected tobamovirus particles. PCR was done using the same tobamovirus PCR (Agdia); following sequencing the virus was identified as TMGMV (GU74404).

TMGMV was first reported in Nglauca from the Canary Islands (McKinney, 1929). There have been a few reports of TMGMV in Capsicum in Asia and Central/South America, the first being in Korea (Choi et al., 2002). It has also been reported in Israel on Torenia fournieri (Scrophulariaceae), Calibrachoa spp. and Petunia spp. (Solanaceae) (Zeidan et al., 2008). Other natural hosts include N. tabacum cv. Samsun, Eryngium aquaticum and E. planum (Brunt et al., 1996). This is the first report of TMGMV in the UK and also the first reported findings in the families Balsaminaceae and Asteraceae. The symptoms of TMGMV on both impatiens and osteospermum make infected plants unsaleable. There is also a concern that infected ornamental plants may act as a reservoir for infection of Capsicum.