Columnea latent viroid
Significance: The Department for Environment, Food and Rural Affairs (UK) has reported two outbreaks of Columnea latent viroid in tomato production nurseries in England (DEFRA, 2007). To prevent further spread of the viroid, restrictions have been placed on the distribution and sale of the fruit and hygiene measures have been implemented at the affected nurseries. Investigations are underway to establish the origin and extent of the infection and whether there are links to other sites. CLVd is considered absent from the United Kingdom and could pose a significant risk to tomato crops.
Issues of Concern: Although the severity of viroid symptoms in tomato may vary, they can be serious, with infected plants displaying symptoms similar to Potato spindle tuber viroid (PSTVd). Chlorosis, bronzing, leaf distortion and growth reductions are possible. Potatoes are considered a natural host for CLVd however, DEFRA reports infections resulting from exposure to infected material are highly unlikely under natural growing conditions. The most effective means of controlling viroid diseases such as CLVd is exclusion and eradication of infected materials. Viroids are easily transmitted by mechanical means and once introduced onto a production site or into a facility they can easily be spread via contaminated cutting tools, on machinery, by handling, or through direct plant-to-plant contact. While the source for these viroids in crops such as tomato is not always clearly understood, many viroids, including the closely related PSTVd, are seed transmitted, suggesting that seed transmission could have played a direct or indirect role in these recent CLVd outbreaks in the UK. In addition, it has been shown that ornamental hosts such as Columnea erythrophae, Brunfelsia undulata, and Nematanthus wettsteinii can be infected by CLVd asymptomatically and serve as reservoirs for the viroid.
DEFRA, 2007. First UK findings of Columnea latent viroid on tomato production nurseries. Department for Environment, Food and Rural Affairs (UK), http://www.defra.gov.uk/planth/newsitems/clvd.htm. Hammond, R.W. 2003. Columnea latent viroid. pp. 231-231 IN Hadidi, A., R. Flores, J.W. Randles,and J.S. Semancik. Viroids. CSIRO Publishing, Victoria, Australia. 370 pp. Hammond, R.W. and R.A. Owens. 2006. Viroids: New and Continuing Risks for Horticultural and Agricultural Crops. APSnet Feature Story, November 2006. http://apsnet.org/online/features/viroids/ Verhoeven, J.Th.J., C.C.C. Jansen, T.M. Willemen, L.F.F. Kox, R.A. Owens and J.W. Roenhorst. 2004. Natural infections of tomato by Citrus exocortis viroid, Columnea latent viroid, Potato spindle tuber viroid and Tomato chlorotic dwarf viroid. European Journal of Plant Pathology Vol. 110(8):823-831.