Organic Treatment Shows Promise Against Xylella

We have been fol­low­ing the devel­op­ments over the years of a study for the con­tain­ment of the Xylella fas­tidiosa (Xf) bac­te­ria led by the research direc­tor of the Olive, Fruit Trees and Citrus Centre of the Council for Agricultural Research and Agricultural Economics Analysis (CREA) in Roma and Caserta, Marco Scortichini, in col­lab­o­ra­tion with other Italian research insti­tu­tions includ­ing the University of Salento in Lecce, and the US Agricultural Research Service Department of Agriculture, in California.

The research was con­ducted to eval­u­ate, both in vitro and in the field, the bac­te­ri­ci­dal activ­ity of a patented com­pound con­tain­ing zinc and cop­per with cit­ric-acid hydracids to con­trol the phy­topathogen.

The pre­lim­i­nary find­ings of the research were pre­sented two years ago dur­ing a sem­i­nar orga­nized by the IOC, and the final results have recently been pub­lished in the peer-reviewed jour­nal devoted to plant pathol­ogy, Phytopathologia Mediterranea.

The researchers car­ried out a three-year field trial in an olive grove in Veglie, in the province of Lecce, con­tain­ing adult Cellina di Nardò and Ogliarola salentina olive trees, which before the trial were offi­cially declared infected by Xylella fas­tidiosa subsp. pauca and showed symp­toms of the olive quick decline syn­drome (OQDS or CoDiRO).

“Experimental field tests are the fun­da­men­tal core of the research since they allow us to under­stand how a phe­nom­e­non works, but a very impor­tant phase is the sub­se­quent imple­men­ta­tion of the trial, which in this case gave us encour­ag­ing results,” Scortichini said. ​“Now, our pro­to­col is cur­rently fol­lowed by some farm­ers in infected areas as a prac­tice to con­tain the dis­ease.”

The researcher said the grow­ers vol­un­tar­ily asked to fol­low the pro­ce­dure, after attend­ing pre-trial meet­ings, since their olive grove had strong symp­toms of the dis­ease. Therefore, in April 2016 they started to imple­ment the pro­to­col, first remov­ing the por­tions of the olive trees affected by des­ic­ca­tion, then apply­ing the treat­ment.

“At the present time, their olive trees are full of olives in excel­lent health,” Scortichini observed. ​“To give an exam­ple, two weeks ago, we counted in some cases, 16 – 18 olives under devel­op­ment on a 12- to 13-cen­time­ter branch.”

Each year dur­ing the trial, from early April to October the com­pound was applied by means of six spray treat­ments on the crowns of the olive trees. The research results showed that the com­pound reduced the sever­ity of symp­toms in both cul­ti­vars. While most untreated trees died by the end of the trial, all treated trees sur­vived with good veg­e­ta­tive sta­tus, accord­ing to NDVI (Normalized Difference Vegetation Index), as recorded in early October 2017.

Quantitative real-time PCR (Polymerase Chain Reaction) was per­formed from June 2016 to September 2017, fol­low­ing the offi­cial pro­ce­dures estab­lished by the European and Mediterranean Plant Protection Organization (EPPO). The analy­sis revealed a sta­tis­ti­cally sig­nif­i­cant decrease of Xylella fas­tidiosa cell den­si­ties within the leaves of treated trees.

“The reduc­tion of the bac­terium is not impos­si­ble — co-exis­tence is some­thing that can be achieved,” Scortichini told Olive Oil Times reporter, Cain Burdeau in the third arti­cle of his inves­tiga­tive series on Xylella.

According to our researcher, as the bac­terium is present over a huge area, at this moment the only solu­tion is to learn how to live with it. ​“To do that, we devel­oped a method aimed at pro­mot­ing the vital bal­ance of the olive trees and the ter­ri­tory, includ­ing the soil,” he pointed out, adding that they con­sider it fun­da­men­tal to rein­tro­duce sta­bi­liz­ing fac­tors in the envi­ron­men­tal sys­tem, through the devel­op­ment of organic and sus­tain­able prac­tices.

(A fur­ther debate con­cerns the oppo­si­tion to this kind of approach by those who see a solu­tion to Xf in pes­ti­cides.

“Therefore, the promis­ing results we achieved sug­gest that an inte­grated man­age­ment which includes reg­u­lar prun­ing of olive trees; soil har­row­ing toward the end of win­ter and the begin­ning of spring, to reduce the pop­u­la­tions of the insect vec­tors which sur­vive on the weeds; and spray treat­ments with this com­pound on the olive trees crowns from spring to the end of autumn, could effec­tively con­trol the dis­ease,” Scortichini con­cluded.