Science News 03/03/2014

Measures to prevent entry of citrus pests are appropriate

Existing measures are effective at protecting the EU from two serious diseases that attack citrus plants

Phyllosticta citricarpa, the organism which causes citrus black spot, and Xanthomonas citri, which causes citrus canker present a risk to the EU citrus industry because host plants are present in Europe and the environmental conditions are favourable. Neither is currently found in the EU and both are subject to control measures preventing their entry into the region.

Citrus black spot

For its assessment of the risk of P. citricarpa to plant health in the EU, EFSA was requested to also assess the risk associated with trade in Tahiti lime (Citrus latifolia). Were current controls and restrictions to be lifted, EFSA’s plant health experts conclude that:

- there is a high risk that would enter the EU via import of citrus plants intended for planting and citrus fruit with leaves. This risk applies to all citrus species – including oranges, mandarins, lemons, grapefruit and limes – as the spores produced by this fungal pathogen on leaves can be dispersed by air;
- there is a risk that P. citricarpa would enter the EU through the import of citrus fruit without leaves, because spores produced on fruit peel can be dispersed by rain splash. To assess this risk, EFSA commissioned a study on how spores found on fruit are spread by rain and wind. For the Tahiti lime fruit without leaves, this risk is considered very low as such spores have never been observed forming on the fruit peel of this citrus species;
- there is a risk that, following entry, P. citricarpa would establish and spread in the endangered citrus growing areas of the EU; simulation models indicate that P. citricarpa woulddevelopin EU citrus growing areas in late summer to autumn and to a lesser extent in late spring to early summer;
- to increase the robustness of the assessment, more data and studies are needed on the epidemiology and impact of this pathogen, particularly in areas at the limits of its current distribution.

Should the disease enter a previously unaffected area, limited options are available to reduce the risk of establishment and spread. Therefore the Panel on Plant Health judges those risk reduction options aimed at preventing the entry of the pathogen into the EU to be the most effective.

The Panel considers the current EU phytosanitary measures – if correctly implemented – to be effective in reducing the risk of P. citricarpa being introduced to the region.

Citrus canker

For its assessment of the risk posed by X. citri to plant health in the EU, EFSA concluded that:

- there is a high risk of entry through import of plants for planting and of ornamental plants;
- there is a low risk of entry through import of fruit due to the low probability of transfer of the bacteria to a suitable host;
- there is a risk that, following entry, X. citri would establish and spread in the endangered area;
- all citrus growing areas of the EU are considered as the endangered area.

As with P. citricarpa, the bacteria is difficult to control once established, hence risk reduction options to reduce the probability of entry are the main means to maintain the absence of this pest. The Panel concludes that prohibition of import of host plants for planting is the most reliable option to reduce the risk of entry. It also recommends additional options for further reducing the risk of entry. The Panel considers that current EU regulations have been appropriate for preventing the introduction of X. citri in the EU.

di S. C.