`New Strain of Plant Germ Killing Ancient Olive Trees in Italy

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New Strain of Plant Germ Killing Ancient Olive Trees in Italy

Jul. 25, 2014
Julie Butler

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Pro­duc­tion on a 5 ha organic olive farm in Italy’s Lecce province fell from 5,000 kg in 2011 to just 400 kg last year as a new strain of the plant pathogen Xylella fas­tidiosa (Xf) made its pres­ence felt.

A report on an audit of the out­break recently pub­lished by the Euro­pean Com­mis­sion said symp­toms started appear­ing on the trees — most of them 200 – 300 years old — about two years ago and by March many were vir­tu­ally dead with only few shoots grow­ing.”

That’s one vignette of the impact of the killer, which the report says was dis­cov­ered in Octo­ber after Ital­ian plant health author­i­ties inves­ti­gated the cause of quick decline syn­drome of olive’ (QDSO) in Lecce, in the region of Puglia, since 2010. It was the first time the pres­ence of Xf in the field had been con­firmed in the EU.

Accord­ing to the report, there is con­sen­sus a new strain (Salento strain) of Xf — genet­i­cally close to one present in Cen­tral Amer­ica — is the cul­prit, together with some fungi and one insect. Infec­tion has also been con­firmed in other plants, namely ole­an­der, almond and pink peri­win­kle.

Old trees more vul­ner­a­ble

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By early this year, Regional Plant Health Ser­vices in Italy esti­mated the sus­pected infected area at 8,000 ha with about 600,000 olive trees — many of them 200 – 500 years old — and a core of 1,000 ha with extremely high mor­tal­ity.” Lecce province has olive pro­duc­tion over about 92,500 ha, about 7% of the total Ital­ian area.

Titled Final report of an audit car­ried out in Italy from 10 to 14 Feb­ru­ary 2014 in order to eval­u­ate the sit­u­a­tion and offi­cial con­trols for Xylella fas­tidiosa,” and made pub­lic ear­lier in July, the report said QDSO is more preva­lent in old trees, and prac­ti­cally in every case, the asso­ci­ated fungi (mainly Phaeocre­mo­nium sp.) and… leop­ard moth (Zeuzera pyrina), are present besides Xf.” On younger trees (up to 20 years old, only a few branches show symp­toms if Xf is present.”

Risk of spread

Car­ried out by the Commission’s Food and Vet­eri­nary Office, the audit found the rel­e­vant author­i­ties in Italy had taken sig­nif­i­cant steps since find­ing the new Xf strain in Octo­ber, includ­ing putting con­di­tions on the pro­duc­tion and move­ment of plants for plant­ing in nurs­eries in the province.

But it said an exten­sive sur­vey to define infected and buffer zones was then still under­way (due to be con­cluded by the end of March). Fur­ther­more, no erad­i­ca­tion or con­tain­ment mea­sures had been taken in the heav­ily Xf infected area of Gal­lipoli and the dis­ease had spread very rapidly. Dis­eased trees are left in place, act­ing as a reser­voir of infec­tion. Unless action is taken, fur­ther rapid spread of the dis­ease must there­fore be antic­i­pated.”

The report also noted the risk of obtain­ing false neg­a­tive results for the dis­ease when using what is known as the ELISA test for other plant species and that the test­ing of dor­mant woody mate­r­ial (e.g. of grapevines) dur­ing win­ter may not be reli­able. Such fac­tors pose a poten­tial risk of the germ’s spread in Italy and abroad. Also, key aspects regard­ing the new Xf strain remain to be clar­i­fied, such as its host range, fac­tors promoting/inhibiting the infec­tion and vec­tors involved, it said.

Among the report’s ten rec­om­men­da­tions are that offi­cial con­trols cover every kind of move­ment of plant­ing mate­r­ial out of Lecce province and that the cus­tomer list for olives and other high-risk plants traded from Lecce in pre­vi­ous sea­sons be given to those parts of Italy and the EU that received such mate­r­ial.

Xf also the cause of Pierce’s Dis­ease in grapevines

At least four Xf sub­species are known, infect­ing dif­fer­ent hosts. The Xf sub­species fas­tidiosa is found in grapevines (and known as Pierce’s Dis­ease), as well as cit­rus, cof­fee and almond; subsp. sandy is found in ole­an­der; subsp. mul­ti­plex in almond, peach, plum, oak, blue­berry, pecan, etc.; and pauca is found in cit­rus and cof­fee.

Since Feb­ru­ary, a new reg­u­la­tion requires EU Mem­ber States to hold annual sur­veys for the pres­ence of Xf in their ter­ri­tory and to report on their first one by the end of Octo­ber.


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