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Scientific Opinion on the risk to plant health posed by Puccinia horiana Hennings for the EU territory, with the identification and evaluation of risk reduction options
The Panel on Plant Health conducted a pest risk assessment for Puccinia horiana Hennings (the causal agent of chrysanthemum white rust) for the EU territory, identified risk management options and evaluated their effectiveness. The assessment was conducted taking into account current EU legislation. The Panel also provided an opinion on the effectiveness of the present EU requirements against this organism, listed in Council Directive 2000/29/EC. Two major pathways for entry were identified: plant material of susceptible hosts for propagation purposes and cut flowers of Chrysanthemum × morifolium. The probability of further entry of the pest was considered unlikely, as the existing certification schemes for propagation material should reduce the risk of importing infected cuttings. For cut flowers, pest transfer to susceptible hosts is associated with the potentially incorrect disposal of cut flower waste within the vicinity of places of production, which is considered a rare event. The probability of establishment and further spread were both considered very likely. The current overall impact in the risk assessment area was considered minor, with medium uncertainty, mainly because standard protective actions are taken in most EU production areas. Risk reduction options to reduce the probability of entry and spread and mitigate the impact were analysed. Council Directive 2000/29/EC addresses mainly the sanitary status of the propagation material. The Directive cannot prevent the entry, establishment and spread, or mitigate the impact, of the pathogen. Were the current regulation to be removed, the frequency of introduction would probably increase. This poses a risk because, although the pest is widespread in the risk assessment area, not all Member States are infested and not all pest pathotypes are present. If a statutory certification system, with associated import requirements for propagation material of host plants, were introduced, this would include practically all prescriptions of the present regulation.
© European Food Safety Authority, 2013
Following a request from the European Commission, the Panel on Plant Health was asked to deliver a scientific opinion on the pest risk of Puccinia horiana, for the EU territory, and to identify risk management options and evaluate their effectiveness in reducing the risk to plant health posed by the organism. In particular, the Panel was asked to provide an opinion on the effectiveness of the present EU requirements against this organism, which are laid down in Council Directive 2000/29/EC, in reducing the risk of introduction of this pest into, and its spread within, the EU territory.
The Panel conducted the risk assessment following the general principles of the “Guidance on a harmonized framework for pest risk assessment and the identification and evaluation of pest risk management options” (EFSA Panel on Plant Health (PLH), 2010) and those of the “Guidance on methodology for evaluation of the effectiveness of options to reduce the risk of introduction and spread of organisms harmful to plant health in the EU territory (EFSA Panel on Plant Health (PLH), 2012). Given the fact that P. horiana (as well as all other harmful organisms listed in Annex IIAII of Directive 2000/29/EC) is already present in the EU territory and has been regulated in the EU for many years, the Panel conducted the risk assessment taking into account the current EU plant health legislation.
After consideration of the evidence, the Panel reached the following conclusions:
With regard to the assessment of the risk to plant health of Puccinia horiana for the EU territory:
Entry—Under the current EU legislation, further entry of P. horiana into the risk assessment area is considered unlikely. Plant material of Chrysanthemum × morifolium cultivars for propagation purposes originating from infested areas may carry P. horiana as teliospores in pustules oras mycelium, both of which are capable of surviving transport and storage conditions and, to some extent, the existing pest management procedures. Nevertheless, the existing certification schemes for the production of propagation material should considerably reduce the risk of importing infected cuttings. Cut flowers of Chrysanthemum × morifolium originating in infested areas might carry the pathogen. However, pest transfer to a susceptible host is associated with the potentially incorrect disposal of cut flower waste within the vicinity of places of production. The Panel considers this to be a rare event. The level of uncertainty associated with entry is medium, as there is lack of data on whether all host plant cuttings imported into the risk assessment area from third countries are actually produced under a sound certification scheme. Furthermore, no information is available on the probability of infected cut flowers or their waste coming into contact with susceptible hosts.
Establishment—New establishment in areas where the pest was not previously present is very likely. The host plants are widespread in the risk assessment area in the open field, in gardens and in greenhouses. The host plants are susceptible as long as green leaves are present (young leaves are more susceptible than mature leaves). The environmental conditions are suitable for infection in most parts of the risk assessment area and at least for part of the host growing season. The pathogen has a reproductive strategy enabling it to reproduce effectively in new environments. Under optimal environmental conditions, a single introduced pustule may be sufficient for establishment. Fungicide-resistant strains also increase the potential for establishment. Exotic strains with unique pathotype profiles may have fewer avirulence genes and therefore may have a higher potential for establishment. Cultural practices and control measures currently applied in the risk assessment area may limit the impact but are not able to prevent the establishment of P. horiana. Climatic control measures (moisture reduction) are applicable and effective only in greenhouses. The proportion of commercial cultivars of chrysanthemum that are resistant to the pathogen is limited. No other obstacles to establishment occur. In addition, the pest has already been detected in most Member States in the risk assessment area where the host is present (AT, BE, BG, CZ, DE, DK, FR, GR, HU, IE, IT, LT, LV, NL, PL, PT, RO, SI, SE, SK, UK). The level of uncertainty associated with establishment is low, as information and data are overall sufficient, consistent and not conflicting; however, there is a lack of data on the survival of teliospores on undried leaves at low temperatures.
Spread—Further spread to areas where the pest was not previously present is very likely. Climatic conditions are suitable for both sporulation of P. horiana and host infection over a wide chrysanthemum-growing area in the EU. The host plants are widespread in the risk assessment area and an important proportion of cultivars (estimated at 10–20 %) is not resistant. Spread by natural means cannot be effectively controlled, although the frequency of vital propagules of the pathogen reaching a susceptible host over a long distance by natural means is low. Outdoor crops (e.g., multiflora) with no climatic control are largely grown in the risk assessment area. There is an important trade in chrysanthemum commodities among and within Member States, and this, as well as other human activities, can help the pest overcome natural barriers (e.g., areas where susceptible hosts are not grown). The level of uncertainty associated with spread is low, as the available information and data are overall sufficient, consistent and not conflicting. However, there is lack of experimental data on the maximum distance over which the basidiospores are dispersed by air currents.
Impact—The current overall impact in the risk assessment area is considered minor. In most EU production areas the pathogen is considered established, and standard protective action is taken in the form of regular protective fungicide treatments and reductions in leaf wetness period where possible. Major breeders also increasingly incorporate resistance genes and successfully self-regulate the production of cuttings. Therefore, a higher impact is expected only in the case in which a crop of a susceptible cultivar is grown in conditions in which leaf wetness period is not or cannot be controlled and where no protective fungicides are applied. Such cases are currently very rare but, if they occur, the impact can be locally severe, especially if cuttings did not undergo a certification scheme and were infected. The level of uncertainty associated with impact is medium. There is uncertainty about the future availability of effective fungicides, which could be reduced owing to legislative restraints, and about the level of fungicide resistance. Were the availability of fungicides to be reduced and fungicide resistance to increase, the control options would decrease and the impact rating would be higher. There is also uncertainty about the stability of the resistance genes currently used in the breeding programmes. If this resistance were to be overcome, for example after the introduction of virulent exotic pathotypes and recombination with established populations, the impact rating would be higher.
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.
The present regulation effectively controls the main pathway for entry into and spread within the risk assessment area of the pathogen. The requirements are fulfilled mainly by producers growing chrysanthemum propagation material subject to certification schemes. No requirements are formulated to prevent entry and spread by pathways other than plants for planting or to mitigate the impact of P. horiana. Currently the pest is widespread in the risk assessment area, although not all EU Member States are infested and not all pathotypes of the pathogen are present.
If a statutory certification system of source propagation material with associated import requirements for propagation material of host plants could be introduced, this would include practically all prescriptions of the present regulation.
The Panel considers the following measures appropriate to substantially reduce the risk of entry of P. horiana into the risk assessment area by the movement of plants for planting (rooted or unrooted cuttings), and cut flowers:
Measures to apply to consignments:
- Demanding phytosanitary certificates is a moderately effective and very highly feasible option, although one with medium uncertainty.
Measures to apply to the growing crop:
- Cultural practices: climate control, avoiding leaf wetness, avoiding overhead irrigation, removal of infested plants and crop residues, spacing of plants, weed control. The effectiveness of these measures is high; in combination with fungicides, in a systems approach, it could be very high. The technical feasibility indoors is moderate, outdoors low. The level of uncertainty is low.
- Chemical treatments: the effectiveness of fungicide sprays is considered high; in a systems approach combined with other risk reduction options, it is considered very high. The technical feasibility is very high—chemical treatments are regularly carried out in places of production. The level of uncertainty is considered medium, because of the possible fungicide resistance.
- Using resistant cultivars: the effectiveness of this risk reduction option is considered high, with moderate technical feasibility and high uncertainty. Some pathotypes of the pest could overcome host resistance. Only 10–20 % of presently used cultivars are considered resistant. Breeding efforts against all known pathotypes have been initiated by major breeders.
- Certification system: in the case of production of cuttings, the effectiveness of a certification system is considered very high—because of the regular inspections and easily recognised symptoms. In the case of production of cut flowers, the effectiveness is high; because of the longer growing period, there is greater possibility for reinfestation by airborne spores. The technical feasibility is also considered very high. The uncertainty is medium, because the pathogen can spread via air.
- Pest freedom of the area and site of production: the effectiveness is high, in the case of regularly organised surveillance. According to the Panel this option is very highly feasible because regular inspections and surveillance should be part of the certification system. The level of uncertainty is low for pest freedom of the production site; however, the likelihood of an infected plant escaping detection in the area of production is higher than that at the site of production; thus the level of uncertainty for pest freedom of the area of production is medium.
The pathogen P. horiana has been established in the risk assessment area but not in all countries and not all pathotypes. New establishment can be prevented only by preventing its entry.
The measures cultural practices, chemical treatments, resistant cultivars, certification system, plant passports (equivalent to phytosanitary certificates) and pest freedom of the area of production and site of production, described under risk reduction options for entry, also apply to spread.
The measures cultural practices, chemical treatments, resistant cultivars, certification system and pest freedom of the area of production and site of production, described under risk reduction options for entry, are also appropriate for reducing the impact of P. horiana on the production of plants for planting (rooted or unrooted cuttings) and also the production of cut flowers.
Chrysanthemum × morifolium, Chrysanthemum spp., European Union, risk reduction, white rust of chrysanthemum