Columnea latent viroid - The Food and Environment Research ...

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Fera Pest Risk Analysis for Columnea latent viroid Authors: Claire Sansford, Jane Morris Version: 3; revision of version 2 (change of personal communication contact from Thailand) Date: 21 st January 2010; version 2 - 13 th October 2009; version 1 - 15 th May 2009 PPP file: 12362 (Matthews-Berry, 2007). There have been no experiments investigating the effect of CLVd on tomato fruit quality. There are no details of the effect that CLVd has had on the UK tomato crop found infected with CLVd in the summer of 2009. UK (2007) and Dutch (Verhoeven et al., 2004) findings have shown that the viroid can spread easily and rapidly within tomato crops. Compared to a UK outbreak of PSTVd at a tomato production nursery in 2003 (Mumford et al., 2004), CLVd is considered potentially more damaging, spreading more rapidly within the crop in the glasshouse than PSTVd did, and apparently causing greater losses (Matthews-Berry, 2007). If CLVd became listed as a quarantine pest by any country to which the UK exports tomato fruit or plants (there is no tomato seed industry), there is the potential for loss of exports, and/or, additional costs being incurred to meet the importing countries phytosanitary requirements. Ornamental hosts Natural ornamental hosts of CLVd are asymptomatic (Owens et al., 1978; Hammond et al., 1989; Singh et al., 1992; Spieker, 1996) and so there are no reports of quality losses for these hosts. If the pathogen becomes established in the UK and becomes listed as a quarantine pest by other countries with requirements for pest-freedom on exported plants (or seeds) there may be economic implications associated with importing country requirements. Potato Potato has the potential to become infected by CLVd but this is yet to occur naturally. Published experimental work suggests that there is a risk of yield and quality reduction should CLVd infect field-grown potato crops as described below: Experimental transmission (by various methods) of CLVd-nem to potato plants of cultivars Katahdin, Kennebec, and Red Pontiac led to ‘mild’ symptoms of leaf size reduction and stunting. Symptoms appeared 3-4 weeks post-inoculation. (Singh et al. 1992). Experimental inoculation of CLVd isolates from tomato to the first leaves of potato plants (cv. Nicola) under glasshouse conditions did not lead to symptomatic leaves. However, progeny tubers that developed from these artificially-infected pIants, exhibited symptoms comprising stunting, star cracking and malformation. The same CLVd isolates were used to inoculate potato plants in the field (under quarantine conditions). These plants were tested for the presence of CLVd two months after inoculation, proving negative, possibly due to cool growing conditions, or low viroid titre, preventing detection using an R-PAGE assay. Tubers forming on these plants, as well as the plants tested initially in the glasshouse, were planted in the field. Plants arising from the tubers harvested from the glasshouse experiments were severely stunted and themselves produced malformed 18
Fera Pest Risk Analysis for Columnea latent viroid Authors: Claire Sansford, Jane Morris Version: 3; revision of version 2 (change of personal communication contact from Thailand) Date: 21 st January 2010; version 2 - 13 th October 2009; version 1 - 15 th May 2009 PPP file: 12362 tubers; one isolate led to death of plants a couple of weeks after emergence. Tubers arising from the field-infected plants were small and often malformed and the plants arising from them had reduced growth. One isolate led to yield losses in tubers of ca. 82%. Field conditions were not optimal for potato however; thus the authors warn that the implications for yield are only indicative. Verhoeven et al. (2004). Cucumber Cucumber has the potential to become a natural host as it is experimentallysusceptible. CLVd isolates from C. erythropae were found to replicate and cause symptoms of disease (undescribed) in the cucumber cv. Suyo (Hammond et al. 1989), and CLVd tomato isolates were found to infect cucumber (Verhoeven et al. 2004). No further details were given. Thus, the potential impact to cucumber is not possible to estimate. Experimentally-susceptible ornamental hosts The experimental hosts G. aurantiaca and S. sinensis did develop symptoms post-inoculation and so as they are ornamental plants there is potential for quality losses. These species could potentially act as CLVd reservoirs in the PRA area. There are currently no data to confirm transmission from these experimental hosts to more economically important hosts such as tomato and potato. However, the EUPHRESCO DEP project will investigate some elements of this (R. Mumford, Fera, UK, personal communication, 2009). 20. What is the pest’s potential as a vector of plant pathogens? None. STAGE 3: PEST RISK MANAGEMENT 21. How likely is the pest to continue to be excluded from the PRA area? Under protection Very likely Likely Moderately likely Unlikely Very unlikely Outdoors Very likely Likely Moderately likely Unlikely Very unlikely CLVd has already entered the UK. The route of entry that led to the outbreaks in UK tomato crops in 2007 is suspected to be tomato seed, but this has not been proven. There were no outbreaks detected in the UK in 2008. However, there was a single outbreak in a tomato crop in 2009; the route of entry for which is unknown. CLVd may also have been brought in to the UK on asymptomatic ornamental hosts. In the absence of suitable phytosanitary measures, CLVd is unlikely to 19
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