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Europe Puzzled by Olive Tree Epidemic

Dec. 3, 2013
Julie Butler

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Scientists are still try­ing to pin­point the causes and deter­mine how to pre­vent the spread of the dev­as­tat­ing dis­ease killing olive trees in the region of Puglia in Italy.

In a recent state­ment, the European Food Safety Authority (EFSA) said that while the plant pathogen Xylella fas­tidiosa (Xf) had been detected in olive trees in the Lecce province last month, its spe­cific role in caus­ing the olive dis­ease is still under inves­ti­ga­tion as fungi and insects have also been reported as asso­ci­ated.

The EFSA report fol­lowed a November 11 request from the European Commission for expe­dited advice. There is an urgent need to put in place mea­sures to pre­vent the spread of this harm­ful organ­ism into other parts of the Union through the move­ment of rel­e­vant plants, plant parts and other prod­ucts,” the Directorate-General for Health and Consumers said.

No way to erad­i­cate Xf

In its report, EFSA said that there is no record of suc­cess­ful erad­i­ca­tion of X. fas­tidiosa once estab­lished out­doors due the broad host range of the pathogen and its vec­tors.”

It said that strate­gies aimed at pre­vent­ing the spread of Xf and con­tain­ing the out­break in Italy should focus on its two main entry path­ways — the move­ment of plants for plant­ing and infec­tive insects in plant con­sign­ments — and based on the inte­grated sys­tem approach.

Controls on plant trade and move­ment rec­om­mended

The lat­ter could com­bine options such as pest free areas; sur­veil­lance; cer­ti­fi­ca­tion, screen­house pro­duc­tion, con­trol of vec­tors and test­ing for plant prop­a­ga­tion mate­r­ial; prepa­ra­tion, treat­ment and inspec­tion of con­sign­ments for the path­way of the infec­tive vec­tors in plant con­sign­ments, EFSA said.

The trade and move­ment of infected plants for plant­ing (but not seeds) is the most effi­cient way for long-dis­tance dis­per­sal of Xf how­ever it is also spread by insect vec­tors (car­ri­ers) that gen­er­ally fly short dis­tances up to 100 metres but can also be trans­ported by wind over long dis­tance or trans­ported on plant con­sign­ments.

Xf has recently twice been inter­cepted in France in infected cof­fee plants from South and Central America, which shows that the prob­a­bil­ity of asso­ci­a­tion with the plants for plant­ing path­way can be rated as likely,” EFSA said.

Importation of cit­rus and grapevine plants into the EU is for­bid­den but the trade in other plant species, such as orna­men­tal plants, is huge and rapid, allow­ing sur­vival of pests and their vec­tor insects, it reported.

More infor­ma­tion needed

EFSA said it is hard to con­trol the spread of Xf by spray­ing insec­ti­cides against the car­ri­ers unless the epi­demi­ol­ogy is very clear. One of the biggest chal­lenges with the olive dis­ease epi­demic in south­ern Italy is that the insect car­ri­ers and the strain asso­ci­ated with the dis­ease are yet to be iden­ti­fied.

EFSA said that for now all xylem-fluid feed­ing insects in Europe should be regarded as poten­tial vec­tors.

Under its sec­tion on rec­om­men­da­tions, it advised that host range, vec­tors, path­ways and risk reduc­tion options are fur­ther assessed, once a com­plete pest risk assess­ment for X. fas­tidiosa is con­ducted for the EU, and once more knowl­edge has been acquired on the Apulian out­break of X. fas­tidiosa.”

What is Xf?

EFSA said that Xf is a bac­te­r­ial plant pathogen trans­mit­ted by xylem-fluid feed­ing insect vec­tors and is

asso­ci­ated with a num­ber of impor­tant dis­eases in a wide range of plants.

Most dis­ease symp­toms are asso­ci­ated with bac­te­r­ial block­age of xylem fluid trans­port through the plant (water and nutri­ents). The symp­toms of this harm­ful organ­ism in sus­cep­ti­ble host plants vary, but include mar­ginal leaf scorch­ing, wilt­ing of foliage and with­er­ing of branches, dieback and stunt­ing with even­tual plant death from severe infec­tions.

The out­break in Italy is char­ac­terised by exten­sive leaf scorch and dieback of olive trees (Olea europaea), some of which are over 100 years old, over a large area esti­mated in 8,000 hectares.”

Xf in Italy

EFSA said that the occur­rence of X. fas­tidiosa was reported in Southern Italy (near Lecce, Salento

penin­sula, Apulia region) last month as caus­ing quick decline symp­toms not only on olive trees (Olea euro­pea), but also ole­an­der and almond trees.

Investigations showed that symp­to­matic olive trees were gen­er­ally affected by a com­plex of pests: X. fas­tidiosa, sev­eral fun­gal species belong­ing to the genus Phaeoacremonium and Phaemoniella, and Zeuzera pyrina (leop­ard moth).”

Is is the first out­break of Xf under field con­di­tions in the European Union.



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