Europe Updates Xylella Risk Assessment

The European Food Safety Authority (EFSA) has pub­lished an update to its 2015 assess­ment of the risk of Xylella fas­tidiosa in the European Union (E.U.).

The update broadly con­cludes that there is no known way to erad­i­cate this plant dis­ease, which is spread by pests, such as the olive fruit fly, but that con­trol mea­sures have been shown to be effec­tive in con­tain­ing its spread.

Experts of the EFSA Panel on Plant Health addressed spe­cific ques­tions, includ­ing the short and long-range spread of Xylella fas­tidiosa and its impacts, the period of time dur­ing which the dis­ease is asymp­to­matic and how to reduce the risk of the infec­tion spread­ing.

“This was a com­plex sci­en­tific chal­lenge with many areas of uncer­tainty, but we have dis­tilled some impor­tant con­clu­sions that will assist risk man­agers, risk asses­sors and researchers,” Stephen Parnell, the chair of the panel’s Xylella fas­tidiosa work­ing group, wrote in an arti­cle on the EFSA web­site.

Computer sim­u­la­tions devel­oped by its experts revealed that south­ern Europe is most at risk of infec­tion through some sub­species of the bac­terium, such as Xylella fas­tidiosa subsp. mul­ti­plex, could also cause infec­tions in north­ern Europe.

Through these sim­u­la­tions, the experts were also able to sim­u­late how Xylella fas­tidiosa could prop­a­gate under dif­fer­ent con­di­tions and over short as well as long dis­tances, and reveal the effec­tive­ness of emer­gency phy­tosan­i­tary con­trol mea­sures if put in place quickly.

“Computer sim­u­la­tions are at the core of this sci­en­tific opin­ion,” Parnell said. ​“The mod­els we have devel­oped are robust and, impor­tantly, flex­i­ble so they can be adapted to explore a wide range of dif­fer­ent sce­nar­ios and sup­port emer­gency plan­ning.”

Regarding the period of time the dis­ease is asymp­to­matic, this can vary depend­ing on the sub­species of the bac­terium and the species of plant affected.

For exam­ple, stud­ies exam­ined by the experts revealed that an olive plant infected with the sub­species Xylella fas­tidiosa subsp. pauca is asymp­to­matic for approx­i­mately 10 months and has a 95 per­cent chance of devel­op­ing symp­toms within a period of four years. This long incu­ba­tion period means that visual inspec­tions are not effec­tive in detect­ing infec­tions and that other meth­ods such as sam­pling and diag­nos­tic test­ing are required.

Measures that have been taken to pre­vent fur­ther infec­tion have included cre­at­ing con­tain­ment zones around infected areas, the destruc­tion of dis­eased plants and pest con­trol.

The effec­tive­ness of buffer zones was found to be rel­a­tive, while bio­log­i­cal con­trol mea­sures only tem­porar­ily reduce but do not elim­i­nate the risk of infec­tion. However, early detec­tion is cru­cial for effec­tive erad­i­ca­tion and to con­trol the spread of the dis­ease. Pest con­trol is also impor­tant: insec­ti­cides used in Italy such as acetamiprid and deltamethrin had a 75 to 100 per­cent effec­tive­ness rate.

The study lists a num­ber of plant dis­eases caused by this plant pathogen trans­mit­ted by insects. These include Pierce’s dis­ease, which attacks grapevines; olive quick decline syn­drome, which dec­i­mates olive groves; cit­rus var­ie­gated chloro­sis, affect­ing cit­rus plants; almond leaf scorch, which infects almond trees; and other leaf scorch dis­eases.

Xylella fas­tidiosa was first detected in olive groves in Puglia, south Italy in 2013. New infec­tions of the bac­terium and its sub­species were sub­se­quently detected in plants in other parts of the E.U., notably on the French island of Corsica and the Provence-Alpes-Côte d’Azur region of south­ern France in 2015. In the past four years, sev­eral more cases were reported in Spain, the Italian region of Tuscany, and in Portugal’s Porto dis­trict.

• European Food Safety Authority


• European Food Safety Authority