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For countries falling under the provisions of 2000/29/EC Annex IIAII legislation, the probability of establishment is rated as very likely, with low uncertainty. For Finland and Sweden, protected zone under the 2000/29/EC Annex IB legislation, the probability of establishment is rated unlikely to moderately likely. Spread can occur through the activity of thrips vectors and through trade of infected hosts.
The probability of spread in Member States under Annex IIAII provisions is evaluated as likely, with low uncertainty. In Finland and Sweden, spread is rated as unlikely to moderately likely, with medium uncertainty. Since TSWV may cause both yield and quality losses in a wide range of hosts, a major impact is predictable in the absence of appropriate control measures, with medium uncertainty.
The risk reduction options evaluated by the Panel are those addressing either the sanitary status of the propagation material (including the provisions of 2000/29/EC Annex IIAII and Annex IB, statutory certification system and the use of voluntary industry standards) or those addressing the control of TSWV epidemic development through actions directed at the virus or at its vectors (including cultural methods to reduce crop infestation and chemical or biological control of thrips vectors). Limitations of the current measures and the potential consequences of repealing the current legislation are discussed.
Following a request from the European Commission, the Panel on Plant Health was asked to deliver a scientific opinion on a pest risk assessment for Tomato spotted wilt virus (TSWV), including the identification and evaluation of risk reduction options.
After consideration of the evidence, the Panel reached the following conclusions:
With regard to the assessment of the risk to plant health of Tomato spotted wilt virus (TSWV) for the EU territory:
Two pathways have been identified for TSWV potential entry in the risk assessment area. The plant products not intended for planting pathway is considered to be of minor significance, based mainly on the unlikely probability of transfer of the pathogen to a host, although a high level of uncertainty applies to this assessment owing to the lack of precise information on some key points. The plants for planting pathway is identified as the most relevant pathway since in this case the pathogen is directly transported along the pathway and can be transferred to a new host if a vector is present. The survival during transport is assessed as very likely with low uncertainty and survival to management procedures is assessed as moderately likely to likely for most Member States and as unlikely to moderately likely for Finland and Sweden, which are covered by a protected zone status. All these various ratings carry a medium level of uncertainty. For this pathway, the probability of association of the pest at origin is assessed as moderately likely to likely, with medium uncertainty. Overall, the probability of entry through the plants for planting pathway is rated as likely with medium uncertainty for most Member States (under the Annex IIAII provisions of Council Directive 2000/29/EC) but as unlikely with medium uncertainty for Finland and Sweden, being a protected zone (under Annex IB of Council Directive 2000/29/EC).
TSWV is among the plant viruses with the widest host range and has been reported in most EU Member States. Likewise, its thrips vector species are widely distributed in all Member States, at least under protected conditions. The cultural practices and control measures, in particular the Annex IIAII provisions for TSWV of Council Directive 2000/29/EC, are unlikely to limit establishment, and the Panel rated the probability of establishment as very likely, with a low level of uncertainty. For the protected zone in the EU, this probability of establishment is lower and rated as unlikely to moderately likely, with a medium level of uncertainty.
Spread can occur both through the activity of thrips vectors and through trade of infected hosts, in particular if the plants are vegetatively propagated. Both mechanisms are very efficient on a local scale, but only trade of infected hosts, in particular the vegetatively propagated ones, is efficient in spreading the virus on a large geographical scale. Spread through trade is expected to be less efficient in the protected zones, where the control of planting material covers all plants species and is not restricted to the 10 plant species listed for TSWV in the Annex IIAII provisions of Council Directive 2000/29/EC. The probability of spread in most Member States is therefore evaluated as likely, with low uncertainty. The probability of spread for the protected zones (Annex IB) is evaluated as unlikely to moderately likely, with a medium level of uncertainty.
Since TSWV may cause both yield and quality losses in a wide range of hosts, a major impact is to be predicted in the absence of appropriate control measures, with medium uncertainty resulting mostly from differences in plant susceptibility and in the technical feasibility of some control measures in specific host crops.
With regard to risk reduction options, the Panel evaluated the phytosanitary measures formulated in Council Directive 2000/29/EC and identified additional risk reduction options where relevant.
TSWV has several biological characteristics that strongly influence its epidemiology, its impact and the effectiveness of the risk reduction options that can be deployed to reduce the associated risks of introduction, spread and impact. The key biological properties identified in this respect are:
- TSWV is a systemic pathogen and, as such, it is very efficiently transmitted by all vegetative multiplication techniques. This explains the importance of the plants for planting pathway.
- Similarly to other viruses, there is no effective curative treatment that can be applied to TSWV-infected plants in a production context. This explains the importance of the prophylactic measures.
- TSWV has an extremely wide host range, which includes more than 1 300 crops and weeds.
- TSWV is efficiently vectored by three widely distributed thrips species in the risk assessment area. Their control via chemical or biological control and adapted cultural practices is essential to the control of TSWV epidemic development and of the ensuing damage to crops.
Considering these biological properties, the most efficient and technically feasible risk reduction options identified by the Panel are those addressing either the sanitary status of the propagation material or the control of TSWV epidemic development through actions directed at the virus or at its vectors. Measures addressing the sanitary status of propagation material include the protected zone status conferred by the provisions of Annex IB of the Council Directive 2000/29/EC as well as the implementation of a statutory certification system with associated statutory import requirements or, alternatively, of potentially lower effectiveness, the use of voluntary industry standards. In contrast, the current measures as applied to most EU Member States (Annex IIAII provisions of Council Directive 2000/29/EC) are evaluated as having a low effectiveness. With regards to the second group of measures, addressing the control of TSWV epidemic development, those showing the greatest effectiveness and technical feasibility include a range of cultural methods to reduce crop infestation and chemical or biological control of thrips vectors. In certain crops where natural resistance against TSWV is available (e.g., tomato, pepper), the breeding of resistant varieties is an additional risk reduction option, although its impact is potentially limited by the existence of resistance-breaking isolates.
Concerning the current legislation and its application, the Panel identified two main shortfalls or limitations: (1) the fact that only 10 host species are currently listed in Annex IIAII for a virus that has one of the broadest known host ranges, and therefore the legislation offers only very partial protection, and (2) the reliance on visual inspection for the control of imported certified planting material of Chrysanthemum when this approach cannot be considered fully reliable.
The Panel concluded that if the current Annex IIAII provisions for TSWV were to be removed, no major impact and consequences would be expected for three main reasons: (1) the current Annex IIAII legislation provides only limited protection at entry by covering only a small fraction of all TSWV host species; (2) the marketing directive, i.e., Commission Directive 93/49/EEC, contribute to reduce the incidence of TSWV; and (3) the voluntary certification schemes in place for Chrysanthemum (and probably likewise for other ornamentals) provide a significant contribution to reducing the spread of TSWV. Protected zone status does not provide complete protection because TSWV entry from third countries and spread through internal trade with other Member States are extremely difficult to control, as shown by recent records of outbreaks in the countries with protected zone status. The panel concludes that lifting of the protected zone status would nevertheless result in a worsening of the TSWV situation in the countries concerned and in an increased necessity for the implementation of thrips management and TSWV control measures.
