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

An inter­na­tional team of sci­en­tists has inves­ti­gated the endur­ing ques­tion of how Xylella fas­tidiosa arrived in Europe and adapted to its new envi­ron­ment.

The study, pub­lished in Microbial Genomics, sheds new light on the ori­gin of the Xylella fas­tidiosa bac­te­ria and how the pathogen has evolved, killing mil­lions of olive trees in Puglia.

While the pres­ence of the bac­terium was orig­i­nally con­firmed in Europe in 2013, there remains very lit­tle infor­ma­tion on the bio­log­i­cal rela­tion­ship between bacteria’s geno­types and host plant species, which is par­tic­u­larly rel­e­vant as Xylella fas­tidiosa con­tin­ues to spread across Europe.

By ana­lyz­ing a pop­u­la­tion of strains from Italian olive trees and closely related genomes from other plant species and loca­tions, researchers have con­cluded that the Italian out­break was caused by a sin­gle cof­fee plant imported from Central America in 2008.

The study spanned five years – 2013 to 2017 – dur­ing which sci­en­tists col­lected twig sam­ples from more than 70 trees with Olive Quick Decline Syndrome, the dis­ease caused by Xylella fas­tidiosa, using a new pro­to­col to extract the trees’ DNA.

The genomic sequences of the Xylella fas­tidiosa iso­late affect­ing the olive trees were then com­pared with three cof­fee and ole­an­der iso­lates from Costa Rica, which had been pre­vi­ously sequenced and were pub­licly avail­able.

Previous stud­ies – and numer­ous reports of cof­fee plants infected with Xylella fas­tidiosa imported into Europe from Central America – iden­ti­fied the same bac­terium in some Center America plants. However, there was no sci­en­tific evi­dence of genetic relat­ed­ness among the cof­fee iso­lates from Costa Rica, and the olive tree iso­lates in Puglia.

The data com­par­i­son of the genetic sequences reported in the study demon­strated that the Xylella fas­tidiosa bac­terium from the olive trees is directly related to Central American vari­ants.

The data also sug­gested that the con­ta­gion occurred with the intro­duc­tion of an ​“asymp­to­matic” infected cof­fee plant, prob­a­bly brought to Italy as an orna­men­tal plant.

The study was led by an inter­na­tional team includ­ing sci­en­tists from the United States, France and Italy.

Among the authors, Italian biol­o­gist Maria Saponari of the National Research Council of Italy in Puglia was the first to detect Xyella fas­tidiosa in the nearby Salento region in 2013.

“Previously thought to be restricted to the Americas, the detec­tion of Xylella fas­tidiosa in Europe has raised new con­cerns world­wide due to its highly nox­ious poten­tial,” she said. ​“The first con­firmed report in Europe in 2013 was soon fol­lowed by its pro­gres­sive detec­tion in sev­eral other E.U. coun­tries.”

“The pathogen grad­u­ally expanded its geo­graph­i­cal range world­wide as well as its abil­ity to form novel asso­ci­a­tions with host plants,” she added. ​“In this frame, we have used a genomic tool to study the processes dri­ving an emerg­ing bac­te­ria toward a plant dis­ease epi­demic.”

“With par­tic­u­lar regard to the spread­ing of the bac­terium across south­ern Puglia, genomic data allowed us to recon­struct the emer­gence of the Olive Quick Decline Syndrome, which led to the death of sev­eral mil­lions of olive trees, with sig­nif­i­cant envi­ron­men­tal, social, polit­i­cal and eco­nomic con­se­quences,” Saponari con­tin­ued.

“Our analy­sis sug­gests that the pathogen had arrived in Italy with a sin­gle intro­duc­tion from Costa Rica, con­firm­ing 2008 as the most likely year when Xylella was intro­duced in Italy,” she added. ​“This is con­sis­tent with Apulian farm­ers’ first reports of infected trees in 2010 since the dis­ease incu­ba­tion period can last more than two years.”

Coffee plants are widely used in gar­dens, vil­las, and resorts: their intense green foliage makes them ideal for dec­o­rat­ing out­door areas.

“While in colder areas, the plant is almost always kept inside; in Salento, it was most likely kept out­side, thus favor­ing the con­ta­gion,” Saponari said.

To prove that Xylella fas­tidiosa could have been trans­mit­ted from one species to another, the researchers also con­ducted exper­i­ments where they inoc­u­lated the bac­te­ria in cof­fee plants and spread the infec­tion to olive trees in a con­trolled way using spit­tle­bugs, the nat­ural vec­tor for Xylella fas­tidiosa.

“Results show that cof­fee plants may rep­re­sent a latent car­rier of the bac­terium,” the researchers con­cluded.

• Microbial Genomics
• Nature