Treatment to Mitigate the Impact of Xylella Fastidiosa Shows Promise in Italy

New evi­dence con­firms that one of the most promis­ing tools to com­bat Xylella fas­tidiosa in Italy is work­ing.

As the new treat­ment, com­posed of zinc, cop­per and cit­ric acid, has shown an abil­ity to mit­i­gate the impacts of the deadly olive tree pathogen, a grow­ing num­ber of farm­ers in the south­ern olive-pro­duc­ing region of Puglia are tak­ing notice.

In a study recently pub­lished in the sci­en­tific jour­nal, Pathogens, a team of researchers assessed the effects of the patented bio-com­plex both in the field and in vitro.

The com­pound has proven to be effec­tive against three strains of Xylella, includ­ing the Pauca sub­species (Xfp), which has spread widely in Puglia.

The bio-com­plex also demon­strated bac­te­ri­ci­dal prop­er­ties in the in vitro exper­i­ments, inhibit­ing biofilm for­ma­tion, which is essen­tial for the devel­op­ment of all three of the tested Xylella strains.

“Our paper can be con­sid­ered a fol­low-up of the pre­vi­ous research about the patented com­pound,” said Marco Scortichini, co-author of the study and research direc­tor of the Olive, Fruit Trees and Citrus Center at CREA (Council for Agricultural Research and Agricultural Economy Analysis).

“After a few years of con­stant treat­ments, we had to eval­u­ate the results of our pro­to­col of cohab­i­ta­tion with Xylella,” he told Olive Oil Times.

To study the effects of the con­trol strat­egy, two olive groves in the most infected areas – the Salento region of south­ern Puglia – were mon­i­tored for three and four years, respec­tively, with mol­e­c­u­lar diag­nos­tic PCR test­ing as the main tool of eval­u­a­tion.

Researchers assessed the field symp­toms and Xfp DNA con­cen­tra­tions in the trees on which the bio-com­plex was used. The pro­to­col strat­egy did not aim to erad­i­cate the bac­te­ria from the ter­ri­tory, which would not be fea­si­ble due to the abil­ity of Xylella to repli­cate in many dif­fer­ent plants. Instead, it aimed to increase the resilience of the olive trees after being infected by the plant pathogen.

“The pro­to­col pro­vides for six treat­ments to be applied in the groves from March to September,” Scortichini said. ​“Protecting the trees with these kinds of inter­ven­tions reminds me of what grape grow­ers reg­u­larly do against the late blight dis­ease.”

The bio-com­plex appli­ca­tion method is also quite sim­ple and requires the trees to be sprayed with the prod­uct, sim­i­lar to what farm­ers cur­rently do with many other agri­cul­tural com­pounds.

The mon­i­tored groves included 41 trees of three dif­fer­ent cul­ti­vars – Leccino, Ogliarola salentina and Cellina di Nardò – all of which are typ­i­cal of Salento.

“When reg­u­larly applied to trees, not only did they return to their nor­mal pro­duc­tion, but the dif­fer­ences in the resilience to Xylella of the dif­fer­ent cul­ti­vars tended to min­i­mize,” Scortichini said. ​“The results of the most sen­si­tive to the bac­te­ria, Ogliarola and Cellina, come close to the reac­tion of the most Xfp-resis­tant Leccino.”

“The bio-com­plex has shown its con­tain­ment qual­i­ties even when diluted,” he added. ​“It can be diluted 1:100 with­out los­ing its effi­ciency.”

However, not all olive trees can be treated. Researchers pointed out that the Xylella con­tain­ment suc­cess depends on the sys­temic absorp­tion of the bio-com­plex. For those olive trees that have already been severely hit by the infec­tion, it might be too late.

“For the cur­rent treat­ment to work, at least 50 or 60 per­cent of the crown must be intact,” Scortichini said.

Still, the treat­men­t’s sys­tem­atic nature makes it of inter­est for future tests that researchers have already planned.

“Thanks to a part­ner­ship with the Invaio com­pany, we have pro­grammed new field exper­i­ments start­ing next March or April, if the cur­rent Covid-19 pan­demic will let us oper­ate in the area,” Scortichini said. ​“The idea is to use a spe­cial san­i­tary agri-machine devel­oped by the Swiss-American com­pany to inoc­u­late a spe­cific dose of the bio-com­plex directly under the cor­ti­cal layer.”

The goal is to expand the num­ber of trees that can be treated while con­tain­ing inter­ven­tion costs.

“We should be able to work on the infected mon­u­men­tal sec­u­lar plants as well,” Scortichini added.

Another area of appli­ca­tion for the bio-com­plex is in the fight against the brown mar­morated stink bug, the spread of which in north­ern Italy has caused exten­sive dam­age to the local agri­cul­ture in recent years.

“The team of pro­fes­sor Alberto Alma at the University of Turin has found that our bio-com­plex can be sprayed on the bugs’ eggs,” Scortichini said. ​“Once done, there is evi­dence that the prod­uct kills the sym­bi­otic bac­te­ria that feed the larva vital pro­teins. Without them, the lar­vae die in 98 per­cent of the cases.”

The results obtained by the first farm­ers to adopt the treat­ment are attract­ing an increas­ing amount of atten­tion from other Apulian grow­ers.

“We are see­ing farm­ers join­ing in the provinces of Lecce, Taranto and Brindisi,” Scortichini said. ​“They are expand­ing the treated areas. We are cur­rently at about 700 hectares and we are see­ing large olive com­pa­nies approach­ing [to learn more about the treat­ment].”

• Pathogens
• Fitogest