Evaluation of field treatments to reduce the impact of Xylella fastidiosa infections in olive trees

So far no effective field applicable therapeutic strategy exists to combat the severe
diseases associated to X. fastidiosa. Therefore, various experimental applications to seek for a
sustainable approach for the mitigation of the impact of the infections on olive trees were explored. In
2015-2016, four field trials were set in the infected area in southern Italy: (i) trial 1 consisted of an
olive grove with medium to high incidence of disease symptoms; (ii) trials 2 and 3 consisted of olive
groves with very low incidence of infected and symptomatic trees and (iii) trial 4 was a new plantation
with 3-years old Xylella-free olive plants. Applications included (i) different elicitors of plant resistance
(fosetyl aluminium, acibenzolar-S-methyl, COS-OGA, σ–β Hairpin proteins, cerevisanae) and (ii) Nacetylcysteine (NAC), a mucolytic agent previously showed to have a beneficial impact in reducing
symptoms associated to X. fastidiosa in citrus (1). Periodic surveys included (i) sampling for laboratory
tests to determine the incidence of the infections; (ii) symptom scoring using 0-5 empirical scale of
severity. The overall results showed that only the treatments with NAC, through endotherapy and/or
complexed to organic substances added to the soil, determined a noticeable amelioration of the
symptoms. None of the elicitors produced any measurable positive impact on the diseased trees.
These preliminary encouraging results, prompted for further targeted experiments currently ongoing.