Study Reveals Potential Economic Impact of Xylella on Spain, Italy, Greece

Researchers from var­i­ous uni­ver­si­ties devel­oped an eco­nomic model to val­i­date the long-term impact of Xylella fas­tidiosa (Xf) on the olive oil indus­tries of Spain, Italy and Greece. They found that the poten­tial cost could be mea­sured in bil­lions of euros if the spread of the dis­ease is not mit­i­gated effec­tively.

The pos­si­ble loss for Italy was esti­mated at €5 bil­lion ($5.42 bil­lion) over the course of 50 years, while Spain and Greece were likely to suf­fer losses of 17 bil­lion euros ($18.44 bil­lion) and 2 bil­lion euros ($2.17 bil­lion) respec­tively over the same time period.

Xf is one of the most dan­ger­ous plant-path­o­genic bac­te­ria world­wide, the researchers noted. It causes quick decline syn­drome on olive trees and many other plant species. In the European Union alone, over 84 host plants for the pathogen have been iden­ti­fied so far.

“Olive quick decline syn­drome could cost bil­lions of euros over the next 50 years in Greece, Italy and Spain,” lead study author Kevin Schneider, of the Wageningen University in the Netherlands, told Olive Oil Times. ​“Even under slow dis­ease spread and the abil­ity to replant with resis­tant cul­ti­vars, pro­jec­tions of future eco­nomic impact in affected coun­tries run in the bil­lions of euro.”

For the sake of the research, a bio-eco­nomic model was con­structed for the strain of the bac­terium detected in Apulia. The model com­bined data from cli­matic-suit­abil­ity mod­el­ing, sim­u­la­tions of the dis­ease spread based on radial range expan­sion, and an algo­rith­mic method to com­pute the eco­nomic impact on olive grow­ers.

An assess­ment period of 50 years was selected due to the slow rate of devel­op­ment of olive trees, and dif­fer­ent intro­duc­tion points and dis­per­sal rates of the pathogen were fed to the model to sim­u­late the future spread of the dis­ease. The spread of the dis­ease was cal­cu­lated at 5 kilo­me­ters (3.1 miles) per year on aver­age, likely to be reduced to 1 kilo­me­ter (.62 miles) per year with the appli­ca­tion of proper con­trol mea­sures. Different sim­u­lat­ing sce­nar­ios accounted for vari­a­tions in the dis­per­sal rate.

Results showed that almost all pro­duc­ing ter­ri­to­ries are sus­cep­ti­ble to infec­tion from Xf, with the affected area vary­ing between 85 and 99 per­cent of the olive groves of each coun­try. Furthermore, an esca­la­tion of the dis­ease match­ing the sim­u­la­tions would cause great eco­nomic dam­age to olive grow­ers and pro­duc­ers. Replacing the affected olive trees with Xf-resis­tant cul­ti­vars would limit the dam­age con­sid­er­ably.

“The find­ings sug­gest that most European pro­duc­tion sites fall into the cli­mat­i­cally suit­able ter­ri­tory for estab­lish­ment and dis­per­sal of the dis­ease,” Schneider explained. ​“In Italy, ces­sa­tion of pro­duc­tion after orchard die-off results in an eco­nomic impact of up to €5.2 bil­lion ($5.7 bil­lion) if the pathogen spreads beyond the cur­rent extent. Replanting orchards with resis­tant vari­eties can lower the impact to €1.6 bil­lion ($1.7 bil­lion). Reducing the annual rate of spread could save up to €1.3 bil­lion ($1.4 bil­lion). Introductions into Greece and Spain could result in an impact between €2 bil­lion and €17 bil­lion ($2.2 bil­lion and $18.4 bil­lion), respec­tively.”

The three coun­tries were the most suit­able for the research scope as together, they account for almost 95 per­cent of European olive oil pro­duc­tion. Southern Italy is severely hit by Xf with almost 17 per­cent of its olive pro­duc­ing ter­ri­to­ries cur­rently infected. Spain also suf­fers from the pathogen spo­rad­i­cally present on the main­land and in some islands, whereas Greece remains unaf­fected.

Schneider also spec­i­fied that, due to its mor­phol­ogy, Greece exhibits an advan­tage over Italy and Spain in the case the pathogen man­i­fests itself on a sin­gle entry point.

“We did find that impacts in Greece were lower than com­pared to Italy or Spain,” he said. ​“While this was influ­enced by a few fac­tors, one key dif­fer­ence was the sea as a nat­ural bar­rier for the spread between the areas of pro­duc­tion. Albeit, that this is based on the assump­tion that we only con­sider one intro­duc­tion of the pathogen and not mul­ti­ple intro­duc­tions.”

A cure for Xf has yet to be dis­cov­ered, Schneider added, empha­siz­ing that plant­ing of resis­tant cul­ti­vars, along with con­trol mea­sures, appeared to be effec­tive in con­trol­ling the spread of the bac­terium.

“Currently, there is no prac­ti­cal cure under field con­di­tions,” he said. ​“While impor­tant research on vec­tor con­trol is ongo­ing, adap­ta­tion through resis­tant trees seems the most promis­ing long-term strat­egy. The find­ings stress the neces­sity to strengthen the ongo­ing research on cul­ti­var resis­tance traits and appli­ca­tion of phy­tosan­i­tary mea­sures includ­ing vec­tor con­trol and inocu­lum sup­pres­sion by remov­ing host plants.”

Furthermore, many olive trees sur­round­ing pock­ets of infected trees can be asymp­to­matic, infected with the pathogen but exhibit­ing no symp­toms of the dis­ease. The study rec­om­mended that a cor­don san­i­taire should be cre­ated in the perime­ter of those pock­ets by remov­ing the symp­tom­less trees. The study stressed that the asymp­to­matic, but infec­tious, olive trees pose a sig­nif­i­cant hin­drance to a pos­si­ble erad­i­ca­tion of the dis­ease.

Unpopular prac­tices like felling seem­ingly healthy olive trees can, how­ever, result in ​“great soci­etal unrest in the affected region,” the researchers warned.

Schneider also acknowl­edged the strictly sci­en­tific approach of the study, leav­ing aside the cul­tural side of the olive tree groves of Europe.

“The study did not account for the cul­tural her­itage value of the European olive trees, many of which are hun­dreds of years old,” he said.

Schneider urged olive grow­ers to seek offi­cial advice and apply the proper mea­sures in coop­er­a­tion with the author­i­ties.

“Farmers need to stay vig­i­lant and adhere to the imposed mit­i­ga­tion mea­sures. Government inter­ven­tions are war­ranted with regard to eco­nomic con­sid­er­a­tions, and gov­ern­ment sup­port for adap­ta­tion strate­gies, such as [devel­op­ing and prop­a­gat­ing] resis­tant vari­eties, is impor­tant,” he said

• Proceedings of the National Academy of Sciences of the United States of America


• The Guardian