Scientists Map Risk of Exposure to Xylella

A new study from the University of Málaga has revealed a broad bio­cli­matic poten­tial for the expan­sion of Xylella fas­tidiosa.

The study, which was done by the uni­ver­si­ty’s geog­ra­phy depart­ment, warned that increased areas of Spain and other coun­tries with tem­per­ate cli­mates are likely to be most exposed to this risk for expan­sion.

The research con­ducted by the uni­ver­sity has led to the devel­op­ment of the first multi-scale and multi-fac­tor model that eval­u­ates the poten­tial regional and global reach of the bac­te­ria, which is very harm­ful to olive trees.

The study also iden­ti­fied the regions with the high­est risk of expo­sure to the bac­te­ria, which include the south of Brazil and the United States, Central America and south­ern Europe.

According to the mod­els, Australia and south­ern Africa are two areas where Xylella may also arrive. Zones beyond lat­i­tudes of 40 to 50 degrees appeared to be at a lower risk.

The rapid spread of Xylella and the seri­ous dam­ages it has caused to Italian olive groves is caus­ing con­cern among pro­duc­ers around the olive oil world. Many are wor­ried that the con­tin­ued spread of the dis­ease will have a poten­tially cat­a­strophic impact on the global olive and olive oil indus­tries.

In Spain, in par­tic­u­lar, the study showed that the Iberian Peninsula is at par­tic­u­larly high risk to the entrance and spread of Xylella, which is already wide­spread in the Balearic Islands. The mod­els iden­ti­fied the Mediterranean coast and the south­west of Spain, with high tem­per­a­tures and a lot of rain in win­ter, as the areas at the high­est risk.

The study also showed numer­ous sim­i­lar­i­ties of the parts of Spain with the high­est risk of con­tract­ing and prop­a­gat­ing Xylella. These included each loca­tion’s prox­im­ity to coastal zones where agri­cul­ture is very present, their inter­me­di­ate pop­u­la­tion den­si­ties, which are well con­nected.

Areas with a lower risk were located in the inte­rior of the penin­sula and had an inter­me­di­ate pop­u­la­tion den­sity.

The map is the first of its kind due to the incor­po­ra­tion of eco­log­i­cal niche mod­els, which ana­lyzed the rela­tion­ship between reg­istries of cur­rent Xylella cases and bio­cli­matic data that eval­u­ated 19 vari­ables related to tem­per­a­ture and rain­fall.

Prior to this research Xylella fastidiosa’s global dis­tri­b­u­tion mod­els had been devel­oped based on the extrap­o­la­tion of very spe­cific regional data.

Oliver Gutiérrez Hernández, a pro­fes­sor at the University of Málaga’s geog­ra­phy depart­ment and Luis García, from Spain’s National Research Council, argued in the study that in order to prop­erly exam­ine the scope for the spread of Xylella, more data than was used in pre­vi­ous stud­ies had to be taken into account.

“In the Anthropocene, geog­ra­phy plays a cru­cial role in the man­age­ment of bio­log­i­cal risks,” the pair wrote. ​“The suc­cess in the man­age­ment of them depends, to a large extent, on our abil­ity to pre­dict the poten­tial geo­graphic ranges of invad­ing organ­isms and iden­tify the fac­tors that pro­mote its spread.”

However, Gutiérrez Hernández and García also acknowl­edged that the study and model they have con­structed have sev­eral lim­its, includ­ing that data has only been taken from areas where Xylella is known to be present. This means data from areas where the dis­ease may also be viable but has not yet been detected has been left out.

The unpre­dictabil­ity of human inter­ac­tion with the dis­ease can also not be com­pletely accounted for in the mod­els.

“Ecological niche mod­els based on bio­cli­matic data under­es­ti­mate the poten­tial dis­tri­b­u­tion when the human beings inter­vene as a vec­tor of the species,” Gutiérrez Hernández and García wrote.

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• University of Malaga