Spread of Xylella Slowing in Puglia, Researchers Say

Summary

Italian sci­en­tific bod­ies reported to par­lia­ment that the spread of Xylella fas­tidiosa, a bac­te­ria affect­ing olive trees, is slow­ing down after years of rapid expan­sion. Researchers are study­ing the rea­sons for this decel­er­a­tion, includ­ing envi­ron­men­tal man­age­ment strate­gies and genetic improve­ments to resis­tant olive tree cul­ti­vars, with the goal of pre­vent­ing fur­ther spread of the dis­ease and mit­i­gat­ing eco­nomic impacts. Various con­tain­ment and recov­ery projects are under­way, includ­ing graft­ing tech­niques on mon­u­men­tal trees to tran­si­tion them to resilient and pro­duc­tive vari­eties, as well as the devel­op­ment of mon­i­tor­ing tools to detect and con­tain out­breaks of the bac­te­ria.

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.”

“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.”

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.

“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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