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Scientists Map Risk of Exposure to Xylella

The study showed that southern Spain and other temperate locations between 40 and 50 degrees latitude are at the greatest risk for the spread of Xylella fastidiosa.

A leaf infected with Xylella fastidiosa.
Apr. 3, 2019
By Rosa Gonzalez-Lamas
A leaf infected with Xylella fastidiosa.

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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 suc­cess in the man­age­ment of (bio­log­i­cal risks) depends on our abil­ity to pre­dict the poten­tial geo­graphic ranges of invad­ing organ­isms and iden­tify the fac­tors that pro­mote its spread.

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.

See more: Xylella fas­tidiosa News

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.

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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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