Xylella Fastidiosa Could Be Contained With Better Monitoring

A new study by Enrico Bucci from the Sbarro Health Research Organization (SHRO) sug­gests that the cur­rent strat­egy for mon­i­tor­ing Xylella fas­tidiosa fails to iden­tify all the infected plants and enables pro­gres­sion of the epi­demic via unde­tected infec­tion hotspots.

The data revealed in Bucci’s report on the effec­tive­ness of cur­rent mea­sures could prove vital for the fine-tun­ing of an effec­tive con­tain­ment strat­egy; which due to the lack of a cure for Xylella offers the best chance of stop­ping the dis­ease in its tracks and pre­serv­ing both the tra­di­tional land­scapes of the impacted Mediterranean coun­tries and their economies.

Bucci told Olive Oil Times that data shows there is a fail­ure in the cur­rent dis­ease mon­i­tor­ing strat­egy. He believes the weak­ness can be attrib­uted to the way in which trees are sam­pled. Whilst the cur­rent focus is on trees dis­play­ing symp­toms; most newly infected plants are usu­ally symp­tom-free and there­fore escape detec­tion.

To effec­tively con­tain the dis­ease the iden­ti­fi­ca­tion of infected trees in pre­vi­ously unin­fected regions must be fol­lowed up with appro­pri­ate con­tain­ment mea­sures such as uproot­ing infected plants and fight­ing the insects respon­si­ble for spread­ing the bac­te­r­ial infec­tion.

“Having unde­tected infected plants means the infec­tion could be present with­out peo­ple being aware of this and if this occurred in a zone with­out manda­tory con­tain­ment mea­sures in place, the infec­tion would spread,” Bucci said.

Bucci’s report states that 98 per­cent of infected olive trees clus­ter in spots within a 100-meter (109-yard) radius; which ratio­nal­izes the cur­rent strat­egy of uproot­ing and destroy­ing all trees located in a 100-meter radius of newly detected infected plants.

However, the sci­en­tist believes that cur­rent mon­i­tor­ing misses many infec­tion hotspots and in order to effec­tively con­tain the epi­demic the iden­ti­fi­ca­tion of infected plants in pre­vi­ously unaf­fected regions is nec­es­sary. Bucci said that even 100 per­cent com­pli­ance with the present uproot­ing con­tain­ment strat­egy would only par­tially stop the spread of the dis­ease.

“Containing the epi­demic requires infec­tion hotspots to be iden­ti­fied, as this is the only way to both mea­sure the effi­ciency of our poli­cies and to apply uproot­ing [which is nec­es­sary to lessen the inocu­lum pres­sure in the newly col­o­nized area],” he said.

Bucci spoke of the need for greater invest­ment in mon­i­tor­ing to pre­vent dire con­se­quences adding, ​“if infected plants escape detec­tion, they can­not be uprooted, and the infec­tion can­not be con­tained.”

However, he abstained from lay­ing blame for the spread of the dis­ease on any­one.

“Phytosanitary offi­cers are fight­ing a vast epi­demic with scarce resources, and the mon­i­tor­ing pro­to­col is a com­pro­mise between avail­able money and staff from one side and the neces­sity to sam­ple as many plants as pos­si­ble from the other side,” he said.

Bucci believes that in any mon­i­tor­ing strat­egy, some infected trees will not be detected due to unavoid­able errors cou­pled with infec­tion hotspot trees that escape uproot­ing due to delays in apply­ing the law as a result of bureau­cracy and people’s hes­i­tancy among other rea­sons.

The sci­en­tific com­mu­nity has gen­er­ally con­cluded that uproot­ing alone would fail to con­tain the epi­demic and as part of the cur­rent con­tain­ment strat­egy weed­ing and insec­ti­cide treat­ments to fight the bac­te­ria are manda­tory.

Bucci told us that unless an effec­tive cure is devel­oped we must focus on con­tain­ment of the infec­tion. He also said that he sup­ports the cur­rent poli­cies of her­bi­cide and insec­ti­cide treat­ments, which cur­rently have no valid alter­na­tive.

The Xylella expert also offered his advice for more effec­tive con­tain­ment of the dis­ease.

“First and fore­most is the need to quickly and cor­rectly apply all the manda­tory con­tain­ment mea­sures,” he said.

Secondly, he called for improve­ments to the cur­rent mon­i­tor­ing pro­to­col, ​“in par­tic­u­lar by sam­pling trees fol­low­ing a pre­de­ter­mined sta­tis­ti­cal scheme, instead of rely­ing on arbi­trary selec­tion by staff.”

Finally, he warned peo­ple against the use of sci­en­tif­i­cally unproven reme­dies and rec­om­mended only the use of reme­dies approved by rep­utable sci­en­tific bod­ies, such as the European Food Safety Authority (EFSA).

Bucci said it may be nec­es­sary, ​“to even­tu­ally replace sen­si­tive cul­ti­vars with more tol­er­ant and resis­tant ones, as has been done in the past for other plant dis­eases.”

The sci­en­tist told Olive Oil Times he no longer believes 100 per­cent erad­i­ca­tion of the dis­ease is a pos­si­bil­ity although it could have been achieved if all con­tain­ment mea­sures had been fol­lowed in the early days.

“We may think to keep the dis­ease under con­trol, espe­cially after the iden­ti­fi­ca­tion of appro­pri­ate reme­dies such a cure or resis­tant cul­ti­vars; but we know that even most human pathogens were never entirely erad­i­cated any­where, and this is also true for plant pathogens,” he said. ​“As in any Darwinian strug­gle between a host and its par­a­sites, we need to change to resist and sur­vive. We can’t expect Xylella to stop nat­u­rally.”

Bucci stated his opin­ion that the Italian gov­ern­ment had not done enough to either halt the spread of the dis­ease nor help Italian olive grow­ers and added that whilst laws were signed, money allo­cated and solu­tions announced; the crude facts told a dif­fer­ent story.

“Ministers are cur­rently on sum­mer hol­i­days, but the bac­terium is not, and new infec­tion hotspots were recently announced,” he said.

Bucci was par­tic­u­larly crit­i­cal of the han­dling of the sit­u­a­tion in Puglia.

“Apulian gov­er­nor Emiliano was con­tin­u­ously con­tra­dict­ing him­self, oscil­lat­ing from con­spir­a­to­r­ial posi­tions to vocal activism. In the mean­time, the term estab­lished for manda­tory erad­i­ca­tion by the regional agen­cies in charge of more than infected 300 plants has passed, and for more than 500 oth­ers is approach­ing.”

The sci­en­tist also thought that regional offices were often par­a­lyzed by bureau­cracy and fre­quently deliv­ered con­fus­ing infor­ma­tion to the pub­lic.

Xylella fas­tidiosa first appeared in the olive groves of Puglia in 2013 and went on to destroy 445,000 acres of Italy’s olive groves before spread­ing to the Balearic Islands, Spain, France, Portugal and Israel, spark­ing fears it could reach as far as Africa, Australia and East Asia.

Whilst efforts to keep the epi­demic under con­trol have largely failed and a cure has yet to be found; an organic treat­ment com­bined with good agri­cul­tural prac­tices was believed by some to have shown promise dur­ing a three year trial in Lecce although Bucci did not agree with this.

Italy-based Bucci works as an inde­pen­dent expert for the analy­sis of sci­en­tific data and is an adjunct pro­fes­sor at Philadelphia’s Temple University. He is also affil­i­ated to the Sbarro Health Research Organization.

• Springer


• Newswise