Spread of Xylella Slowing in Puglia, Researchers Say

As the number of severity of new infections deccreases in the southern Italian region, farmers begin to plant and graft resilient varieties.
Emmanuel Sanarica
By Paolo DeAndreis
Jun. 20, 2023 16:04 UTC

Italy’s main sci­en­tific bod­ies ded­i­cated to agri­cul­tural research and com­bat­ing the spread of Xylella fas­tidiosa told par­lia­ment that the spread of the bac­te­ria is slow­ing down.

It has been 10 years since the Xylella out­break asso­ci­ated with the dry­ing up of olive trees was dis­cov­ered,” Donato Boscia, research direc­tor at the National Research Council (CNR), one of the first to iden­tify the bac­terium, told Italian rep­re­sen­ta­tives. And its abil­ity to infect is now declin­ing.”

As of today, we do not have a cure for Xylella, but an inte­grated approach that allows us to main­tain a lower level of infec­tion is pro­duc­ing results.- Pio Federico Roversi, direc­tor, CREA’s National Institute for Plant Protection

In the first seven to eight years, Xylella expanded enor­mously,” he added. The infec­tion that at first encom­passed 8,000 hectares mul­ti­plied its reach on the ter­ri­tory by 100. Today, approx­i­mately 40 per­cent of Puglia is affected at dif­fer­ent lev­els by the epi­demic and con­tain­ment pro­to­cols.”

The news is that in the last two years, the infec­tive capac­ity of the bac­te­ria decel­er­ated,” Boscia con­tin­ued. We can see that, both by the reduc­tion in Xylella’s abil­ity to spread to new areas and by the slower pro­gres­sion of the ill­ness in infected plants.”

See Also:Xylella Arrived in Italy from a Costa Rican Coffee Plant, Researchers Say

CNR researchers are study­ing the rea­sons for Xylella’s decel­er­a­tion. One pos­si­ble rea­son is an envi­ron­men­tal man­age­ment strat­egy that has made it more dif­fi­cult for the insect vec­tors of the bac­te­ria, such as the mar­morated stink bug, to repro­duce.

Along with the olive tree, sev­eral dozen other local plant species in Puglia are sus­cep­ti­ble to Xylella fas­tidiosa.

Xylella fas­tidiosa

Xylella fas­tidiosa is a bac­te­r­ial plant pathogen that affects a wide range of plant species. It is a Gram-neg­a­tive bac­terium that resides in the xylem, the water-con­duct­ing tis­sues of plants. Xylella fas­tidiosa is known to cause a seri­ous plant dis­ease called Xylella fas­tidiosa dis­ease (XFD), which can lead to sig­nif­i­cant eco­nomic losses in agri­cul­ture and forestry.

Xylella fas­tidiosa is trans­mit­ted pri­mar­ily by xylem-feed­ing insects, such as sharp­shoot­ers and spit­tle­bugs, which acquire the bac­terium while feed­ing on infected plants and then spread it to healthy plants. The bac­terium col­o­nizes the xylem ves­sels of the host plant, block­ing water trans­port and dis­rupt­ing the flow of nutri­ents, which results in var­i­ous symp­toms and ulti­mately the decline and death of the infected plant.

The range of plant species affected by Xylella fas­tidiosa is exten­sive and includes both agri­cul­tural crops, such as grapes, cit­rus, almonds, and olives, as well as numer­ous orna­men­tal and land­scape plants. The symp­toms of Xylella fas­tidiosa infec­tion can vary depend­ing on the host plant, but com­mon signs include leaf scorch, wilt­ing, yel­low­ing, stunted growth, and dieback of branches.

Xylella fas­tidiosa has gained sig­nif­i­cant atten­tion in recent years due to its impact on var­i­ous agri­cul­tural indus­tries world­wide. Outbreaks of Xylella fas­tidiosa have occurred in regions such as Europe, North and South America, and Asia, lead­ing to the imple­men­ta­tion of strict quar­an­tine mea­sures and the destruc­tion of infected plants to pre­vent fur­ther spread.

Efforts are being made to under­stand the biol­ogy of Xylella fas­tidiosa, develop detec­tion meth­ods, and explore strate­gies for man­ag­ing and con­trol­ling its spread. However, Xylella fas­tidiosa poses sig­nif­i­cant chal­lenges due to its abil­ity to infect a wide range of plant species, its mul­ti­ple insect vec­tors, and the lack of effec­tive treat­ments once a plant is infected.

In the first few years of the epi­demic, approx­i­mately 95 per­cent of the vec­tor insects mon­i­tored in sev­eral loca­tions tested pos­i­tive to the bac­te­ria,” Boscia said. This per­cent­age is now down to 25 to 30 per­cent.”

At spe­cific times of the year, Apulian author­i­ties, farm­ers and cit­i­zens in the at-risk areas exe­cute a series of land man­age­ment actions to reduce the oppor­tu­ni­ties for the vec­tor insects to repro­duce.

What we are see­ing is that the rules against plan­ta­tions that might be sen­si­tive to Xylella and the timely destruc­tion of the infected plants by the farm­ers are play­ing a cru­cial role in this chang­ing sce­nario,” Boscia noted.

Both CNR and the Council for Research in Agriculture (CREA) under­lined the sig­nif­i­cance of cur­rent research inves­ti­gat­ing the role of genet­ics in efforts to curb the spread and mit­i­gate the eco­nomic impacts of Xylella.

That might help us pre­vent or delay the fur­ther spread of the ill­ness,” Pio Federico Roversi, direc­tor of CREA’s National Institute for Plant Protection, told Italian rep­re­sen­ta­tives.

Stefania Loreti, a sci­en­tist of the National Bacteriology Laboratory at CREA, told par­lia­men­tar­i­ans that the prac­ti­cal effects of genetic improve­ments to olive trees would require 10 to 15 years to bear fruit.

Italian researchers have iden­ti­fied the Leccino and Favolosa (Fs-17) cul­ti­vars as the only two Xylella-resis­tant olive trees.

Genetic improve­ment is cru­cial, as Leccino and Favolosa are not enough to re-pop­u­late the whole Apulian olive tree land­scape,” Loreti said. We are now research­ing mol­e­cules able to kill the Xylella bac­te­ria [with­out dam­ag­ing other plant tis­sues].”


Local olive grow­ers are look­ing increas­ingly at Leccino and Favolosa graft­ing. CNR researchers have found that these grafts allow trees oth­er­wise sen­si­tive to Xylella to cope with the infec­tion suc­cess­fully.

That is part of our action against Xylella,” Emmanuel Sanarica, the award-win­ning pro­ducer of Ulive, told Olive Oil Times.

The farm where we are apply­ing our anti-Xylella strat­egy is within the red zone [where active Xylella infec­tions have been iden­ti­fied],” Sanarica said. That means we have lim­its on the vari­eties we can plant there, as only Leccino and Favolosa are allowed.”

Since 2018, our goal has been to save mon­u­men­tal [milen­nary] trees that have been here for cen­turies, wit­nesses of time,” he added. Some of them have a diam­e­ter exceed­ing three meters; we could not stand their demise. So we began remov­ing their crowns and graft­ing Leccino and Favolosa cut­tings.”

Through this type of graft­ing, Sanarica hopes to tran­si­tion these land­marks of the Apulian land­scape from sus­cep­ti­ble to resilient and pro­duc­tive vari­eties. He expects the process to take three years.

I per­son­ally man­aged the graft­ing, given the sig­nif­i­cance of those trees,” Sanarica said. We have 120 trees par­tially or com­pletely grafted. That hap­pens as after the first graft­ing; we pro­ceed to a few oth­ers to fully rein­state the crown of the trees.”

Sanarica empha­sized how the graft­ing oper­a­tions do not turn the ancient trees into com­mon Leccino or Favolosa trees.

What we are find­ing out is that the new fruits are greatly impacted by the vigor of those huge trees,” he said. Their olive oil is dif­fer­ent from what you could expect with those two cul­ti­vars; they bear a dif­fer­ent sen­so­r­ial out­come. We are very happy with the first results, and we plan to go ahead with our strat­egy.”

This tech­nique should be more con­sid­ered, but I know some [farm­ers] are afraid to lose pro­duc­tion,” he added. In real­ity, it is a brave choice, but we need to save those trees to pre­serve our his­tory and ter­ri­tory.”

Coldiretti and Unprol, Italy’s main farm­ers’ and olive oil pro­duc­ers’ asso­ci­a­tions, are also test­ing the graft­ing tech­niques as part of a broader con­tain­ment and recov­ery project.

What we are doing now, on 100 mon­u­men­tal trees, is to cut their crown and graft Leccino cut­tings,” Nicola Di Noia, Unaprol’s gen­eral direc­tor, told Olive Oil Times. We expect those trees not to bear fruit for approx­i­mately four years.”

As of today, we do not have a cure for Xylella,” Roversi con­firmed to par­lia­ment, but an inte­grated approach that allows us to main­tain a lower level of infec­tion is pro­duc­ing results.”

This approach also includes sev­eral kinds of treat­ments as well as actions to sus­tain the nour­ish­ment of the olive trees by tak­ing care of the soil, which in south­ern Puglia is tra­di­tion­ally poor,” he added. Several treat­ments are under­go­ing test­ing.

According to Italian sci­en­tists, easy, fast, inex­pen­sive and sim­ple-to-use solu­tions to mon­i­tor the spread­ing of the bac­te­ria are cur­rently under devel­op­ment and par­tially in use.

Roversi cited some of the many mon­i­tor­ing tools in the field beside the lab­o­ra­tory, such as dogs trained to iden­tify infected plants or sin­gle-use kits that can help the bor­der author­i­ties mon­i­tor the huge amount of plants being moved into and out of the region.

Thorough mon­i­tor­ing of the region is cru­cial, as timely action is essen­tial,” Roversi said. It means that if an out­break hap­pens in a new area, it is vital to be able to iden­tify it imme­di­ately. That out­break might be lim­ited to only a few plants and, if they are iden­ti­fied and removed in time, it can be effi­ciently con­tained.”


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