First identification of Tobacco mild green mosaic virus on Capsicum annuum in Taiwan

Peppers (Capsicum annuum) are important vegetables and some cultivars are planted as ornamental plants because of their colourful fruits. In 2003, mild chlorosis and necrotic lesions (Fig. 1) were observed on pepper plants in northern part of Taiwan. When pepper leaf extracts from plants showing symptoms were mechanically inoculated onto leaves of Chenopodium amaranticolor and C. quinoa, chlorotic lesions developed on the inoculated leaves. After three successive single lesion isolations on C. amaranticolor, an isolate of a virus was obtained. This isolate caused only local lesions on inoculated leaves in many Nicotiana species but produced systemic mosaic on N. benthamiana and N. debneyi. In addition, inoculated pepper plants produced mild chlorosis symptom, that later became necrotic and were followed by leaf drop.

Transmission electron microscopy revealed numerous rigid rods, approximately 300 nm in length. This strongly suggested that this virus isolated was a tobamovirus. According to the literature, at least six tobamoviruses are able to infect peppers: Paprika mild mottle virus (PaMMV), Pepper mild mottle virus (PMMoV), Ribgrass mosaic virus (RMV), Tobacco mild green mosaic virus (TMGMV), Tobacco mosaic virus (TMV) and Tomato mosaic virus (ToMV) (Brunt et al., 1996). To identify the unknown virus, a poly(A) tail was added to the 3' end of the purified viral RNA using poly(A) polymerase and cDNA fragments were subsequently amplified using a SMART™ RACE cDNA Amplification Kit (BD Biosciences, Palo Alto, CA, USA), before being cloned into a pGEM-T® Easy Vector (Promega, Madison, USA). Two independent clones were sequenced and a BLAST search was performed against the NCBI database. The results clearly indicated that the clones contained a partial sequence of TMGMV, with a 98% nucleotide identity to a Japanese isolate of TMGMV (accession number AB078435). To our knowledge, this the first report of TMGMV identified in Taiwan.