Pest risk assessment of Radopholus similis for the EU territory

Abstract

The Panel on Plant Health performed a pest risk assessment on Radopholus similis, the burrowing nematode for the EU. The quantitative assessment focused on entry, establishment, spread and impact on tropical and subtropical ornamental host plants, the main pathways for entry of R. similis into the EU. Infested consignments are expected to enter the risk assessment area on ornamentals under all scenarios. For citrus, which is a closed pathway for entry, outdoor establishment was assessed. Establishment may only take place after successful transfer from ornamental plants to citrus production systems. This event is called 'shift' in this assessment, to indicate that this is an unusual transfer. It has been estimated that establishment of this nematode in the open field in the EU citrus production areas under current temperatures is possible in most parts of the citrus production area in the EU. Temperature conditions will prevent the nematode from establishing only in the northernmost citrus areas and at higher altitudes in the south. Host plants for planting originating from infested places of production (greenhouses) within the risk assessment area are considered the main pathway for spread within the risk assessment area. Under current climatic conditions, the population of R. similis is not expected to reach damaging population levels in the open field. In case of increased temperatures due to global warming, the nematode population may reach damaging levels in very few places outdoors. Currently, main impact is considered for ornamental greenhouse production in the risk assessment area. Impact will be either caused by direct plant growth reductions or loss due to phytosanitary measures applied on regulated plants. Despite the fact that R. similis is globally considered as one of the most destructive plant parasitic nematodes, the impact in the risk assessment area is considered low.

Guidance on quantitative pest risk assessment

“…4) The impact step is again conceptualised at the level of the whole of the EU. In previous opinions in which the single plant was used as a spatial unit in the spread step (Diaporthe vaccinii, Ditylenchus destructor, E. lewisi, R. similis -see EFSA PLH Panel, 2016b, 2017a, impacts in natural areas were not accounted for. Impact on the plant production system' can be assessed using expert knowledge on the relationship between the density of the pest or severity of disease and the yield loss.…”

“…This is straightforward. This was carried out in opinions on Ditylenchus destructor and R. similis (EFSA PLH Panel, 2016b, 2017a. If the spread is modelled at the level of NUTS regions, elicitation or modelling is needed to assess the impact, taking into account that within a NUTS region, there will be spatial heterogeneity in the occurrence (presence) and density of the organism.…”

“…This is in line with EFSA policy of transparency, the risk model implementation and calculation procedure will be published as supplementary material along with the Panel opinion. Figure 7 shows an example user interface where @Risk TM and Microsoft Excel TM are used to fit uncertainty distributions to quantile value estimates obtained by expert elicitation during work on the EFSA risk assessment for R. similis (EFSA PLH Panel, 2017a). By interactive choice of distribution type by the user, the software will simulate a number of randomly drawn values from the distributions so that the shape of the uncertainty distributions can be visualised both by histogram of the randomly drawn values and by cumulative probability curves along with quantile estimates from expert elicitation.…”

“…Other choices may be made by the risk assessors if their organism and data justify a different choice. In several opinions (Diaporthe vaccinii, Ditylenchus destructor, E. lewisi, R. similis -see EFSA PLH Panel, 2016b, 2017a, spatial units in terms of administrative areas were not used, but spread was assessed using the single plant as a unit that would be either 'infested' or 'not infested'. This option makes the calculation of impact easier.…”

“…Screenshot of parameter specification for a part of a risk model using @Risk TM and Microsoft Excel TM . The current example is taken from the EFSA risk assessment of Radopholus similis(EFSA PLH Panel, 2017a) • Uncertainties about the identification and selection (or exclusion) of evidence used in the assessment, (e.g. in cases of complex taxonomy there could be confusion in the literature on features of the species).…”