` Expert Says Eradication of New Olive Tree Disease in Europe Unlikely


Expert Says Eradication of New Olive Tree Disease in Europe Unlikely

Mar. 29, 2014
By Julie Butler

Recent News

Donato Boscia

Will Italy be able to erad­i­cate the dis­ease which has already infected 8,000 ha of olive groves in Lecce, on the Salento penin­sula? And what is the risk of the plant pathogen behind it – Xylella fas­tidiosa (Xf), also the cul­prit in Pierce’s dis­ease – spread­ing to olive trees else­where in Italy and wider Europe?
Olive Oil Times put these and other ques­tions to one of the lead­ing experts on the out­break, plant virol­o­gist Dr. Donato Boscia, from the Insti­tute of Plant Virol­ogy (IVV) at the National Research Coun­cil, in Bari, Italy.

Boscia spoke in the wake of a Euro­pean Union-wide ban on move­ment of cer­tain plants out of Lecce to help pre­vent spread of the dis­ease. EU mem­ber states must also start annual checks for the pres­ence of Xf.

A major pest in the grapevine and cit­rus indus­tries in trop­i­cal, sub­trop­i­cal and tem­per­ate areas of the Amer­i­cas, until the Lecce out­break in mid-Octo­ber there had been no con­firmed reports of Xf in Europe, though there was an uncon­firmed report in vine­yards in Kosovo in the 1990s.

What is the cur­rent extent of the Xf infec­tion in Apu­lia?

Dr. Donato Boscia: A large regional sur­vey, done by sam­pling and ana­lyz­ing 16,000 plants, has been car­ried out in the Apu­lia region, in south-east Italy. It was con­firmed that the pathogen is actu­ally con­fined to the province of Lecce, while the remain­ing cen­tral and north­ern part of the region are free.

Xylella fas­tidiosa

Is erad­i­ca­tion pos­si­ble?

I feel that even a severe and ambi­tious pro­gram of erad­i­ca­tion will not have much chance of suc­cess because:

1. The con­t­a­m­i­nated area has a very large exten­sion.
2. The pathogen has sev­eral sus­cep­ti­ble hosts, and surely sev­eral of those are still unknown and may be symp­tom­less.
3. Effi­cient insect vec­tors (car­ri­ers) are involved.
4. The area is densely pop­u­lated, with an infi­nite num­ber of pri­vate houses with gar­dens, which makes unre­al­is­tic to expect to get all of them sam­pled and even­tu­ally erad­i­cated.

In my per­sonal opin­ion these four ele­ments make it very dif­fi­cult, if not impos­si­ble, for an erad­i­ca­tion pro­gram to suc­ceed.

Is this strain of Xf likely to spread to olive or other trees in other parts of Italy and beyond?

That’s dif­fi­cult to say. Due to the geo­graphic posi­tion of the out­break there is no risk of spread to other parts of Italy or Europe through insect vec­tors (car­ri­ers). How­ever, though move­ment of sus­cep­ti­ble plants is for­bid­den, any ille­gal or uncon­trolled plant move­ment may rep­re­sent a major risk.

What are the symp­toms of Xf?

They con­sist of the with­er­ing and des­ic­ca­tion of ter­mi­nal shoots dis­trib­uted ran­domly but which then expand to the rest of the canopy, thus result­ing in the col­lapse and death of the trees. In the affected groves, the total­ity of the plants are symp­to­matic.

What is cur­rently hap­pen­ing in Apu­lia in rela­tion to the out­break?

So far there are two main actions being taken by the Regional Plant Pro­tec­tion author­i­ties. First, in the con­t­a­m­i­nated area as well as in the whole province of Lecce, the move­ment of plant mate­ri­als of sus­cep­ti­ble species is pro­hib­ited. Sec­ond, a sur­vey of the whole region aimed at iden­ti­fy­ing and delim­it­ing the infested areas, the buffer zones and the secu­rity zones is due to be by April 1.

Until these areas have been delim­ited though a large scale sur­vey, there is no pos­si­bil­ity to start any effec­tive pro­gram of the uproot­ing and removal of infected plants.

It has to be said that the out­break was iden­ti­fied only five months ago, and that the rel­e­vant ter­ri­tory is very large – 8,000 ha of olive orchards dis­trib­uted in a ter­ri­tory at least twice as large. More­over, other minor spots came out dur­ing the mon­i­tor­ing. This work is almost com­pleted and addi­tional phy­tosan­i­tary mea­sures — such as tree removal — are under dis­cus­sion and nego­ti­a­tion with the Euro­pean Com­mis­sion Direc­torate Gen­eral for Health and Con­sumers.


What is the research now focused on?

Epi­demi­o­log­i­cal stud­ies under­way fol­low four dif­fer­ent routes:

1. Iden­ti­fi­ca­tion of nat­ural sources of inocu­lum (nat­ural flora). This is essen­tial to plan fur­ther actions of con­tain­ment, under­stand the real pos­si­bil­i­ties of suc­cess with an erad­i­ca­tion pro­gram, bet­ter under­stand the risk of fur­ther spread, and define the list of species banned from trade.
2. Cap­ture of leafhop­pers thriv­ing on the nat­ural flora, their iden­ti­fi­ca­tion and analy­sis for the pres­ence of Xf
3. Trans­mis­sion tri­als using Xylella-pos­i­tive insects
4. Place­ment of bait plants in infected olive groves.

The char­ac­ter­i­za­tion of the geno­type is well advanced, and results will be pub­lished soon.

What strain of Xf is the cause?

DNA analy­sis shows the pop­u­la­tion of X. fas­tidiosa affect­ing olive trees in Italy is an atyp­i­cal vari­ant of the sub­species pauca”, the one known to cause Cit­rus Var­ie­gated Chloro­sis in Brazil. For­tu­nately, our vari­ant is unable to infect cit­rus or grapevine.

When might char­ac­ter­i­sa­tion of the geno­type be com­plete and how might that help?

The sequence of the whole genome is almost com­plete and will prob­a­bly be pub­lished in a cou­ple of months, though a geno­type with the same sequence type has already been iden­ti­fied, giv­ing the pos­si­bil­ity of soon get­ting impor­tant ele­ments to assess the path­way of entrance of the pathogen in Europe and impor­tant infor­ma­tion on its bio­log­i­cal prop­er­ties.

What was the lead-up to the out­break?

A dev­as­tat­ing dis­ease known as quick decline syn­drome of olive” (OQDS) appeared sud­denly a few years ago in olive trees, many of them cen­tury-old trees, in the vicin­ity of Gal­lipoli, in the Lecce province. By late last year it had exploded in epi­demic form, so as to affect the esti­mated sur­face area of over 8,000 hectares.

Sam­ples from olive trees were sub­jected to mol­e­c­u­lar analy­sis which gave pos­i­tive results for Xf. Almond (Prunus dul­cis) and ole­an­der (Ner­ium ole­an­der) plants grow­ing near affected olive trees and show­ing symp­toms of leaf scorch also tested pos­i­tive.

In the mid­dle of last Octo­ber, the Insti­tute of Plant Virol­ogy of the National Research Coun­cil (CNR) and the Uni­ver­sity of Bari informed the local phy­tosan­i­tary author­i­ties of the detec­tion of the Xf bac­terium in Lecce and the move­ment of prop­a­ga­tion mate­r­ial of any sus­cep­ti­ble host species from the infected area was promptly pro­hib­ited by the Regional Plant Pro­tec­tion Ser­vice.

What is the pur­pose of the com­ing First Inter­na­tional Sym­po­sium on the Euro­pean out­break of Xylella fas­tidiosa in olive?”

The sym­po­sium will be held in Gal­lipoli from Octo­ber 21 – 22 and be fol­lowed by tech­ni­cal lab­o­ra­tory work­shops from Octo­ber 23 – 24. It will offer a detailed overview of this emerg­ing threat and pro­vide a great oppor­tu­nity to exchange infor­ma­tion with the main inter­na­tional experts on this topic.

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