First Report of Tomato torrado virus Infecting Tomato in Colombia
Authors: Verbeek M. , Dullemans A. M. 
Published: January 2012

Tomato (Solanum lycopersicum L.) plants grown in plastic greenhouses near Villa de Leyva, northeast of Bogota, Colombia showed necrotic spots on the leaves in September 2008. Initial symptoms were necrosis beginning at the base of leaflets that were surrounded by yellow areas. These symptoms resembled those described for Tomato torrado virus (ToTV; family Secoviridae, genus Torradovirus), which was first found in Spain (2). Other (tentative) members of the genus Torradovirus, Tomato marchitez virus (ToMarV), Tomato chocolate spot virus (ToChSV), and Tomato chocolàte virus (ToChV) (3) induce similar symptoms on tomato plants. One sample, coded T418, was stored in the freezer and brought to our lab in 2011. Serological tests (double-antibody sandwich-ELISA) using polyclonal antibodies (Prime Diagnostics, Wageningen, The Netherlands) on leaf extracts showed the absence of Pepino mosaic virus (PepMV), Tobacco mosaic virus (TMV), Tomato spotted wilt virus (TSWV), Cucumber mosaic virus (CMV), Potato virus X (PVX), and Potato virus Y (PVY). Leaf extracts were mechanically inoculated onto the indicator plants Physalis floridana, Nicotiana hesperis ‘67A’, and N. occidentalis ‘P1’ (six plants in total) and were kept in a greenhouse at 20°C with 16 h of light. Necrotic symptoms appeared 4 to 5 days postinoculation and resembled those described for ToTV (2). Two dip preparations of systemically infected P. floridana and N. occidentalis leaves were examined by electron microscopy, which revealed the presence of spherical virus particles of approximately 30 nm. To confirm the presence of ToTV, total RNA was extracted from the original leaf material and an inoculated P. floridana and N. occidentalis plant using the Qiagen Plant Mini Kit (Qiagen, Hilden, Germany) following manufacturer's instructions. ToTV-specific primer sets ToTV-Dp33F/ToTV-Dp20R (5′-TGCTCAATGTTGGAAACCCC-3′/5′-AGCCCTTCATAGGCTAGCC-3′, amplifying a fragment of the RNA1 polyprotein with an expected size of 751 bp) and ToTV-Dp1F/ToTV-Dp2R (5′-ACAAGAGGAGCTTGACGAGG-3′/5′-AAAGGTAGTGTAATGGTCGG-3′, amplifying a fragment on the RNA2 movement protein region with an expected size of 568 bp) were used to amplify the indicated regions in a reverse transcription (RT)-PCR using the One-Step Access RT-PCR system (Promega, Madison, WI). Amplicons of the predicted size were obtained in all tested materials. The PCR products were purified with the Qiaquick PCR Purification Kit (Qiagen) and sequenced directly. BLAST analyses of the obtained sequences (GenBank Accession Nos. JQ314230 and JQ314229) confirmed the identity of isolate T418 as ToTV, with 99% identity to isolate PRI-ToTV0301 in both fragments (GenBank Accession Nos. DQ388879 and DQ388880 for RNA1 and RNA 2, respectively). To our knowledge, this is the first report of ToTV in Colombia, and interestingly, since ToTV has been found only in Europe and Australia (1) so far, this is the first report of ToTV on the American continent.

References: (1) C. F. Gambley et al. Plant Dis. 94:486, 2010. (2) M. Verbeek et al. Arch. Virol. 152:881, 2007. (3) M. Verbeek et al. Arch. Virol. 155:751, 2010.