Leaves sampling

Three samples constituted by a statistically representative number of mature leaves (20 leaves) were collected on going from the North to the Southside of the full canopy for each of the four trees at day 0 (before injection) and 0.25, 1, 2, 4, 7 and 15 days after the injection. All the 84 total collected leaf samples were placed in coded plastic bags into a refrigerated box and taken to the laboratory. Samples were therefore stored at − 20 °C until metabolomic analysis. Associated symptoms incidence for the examined trees were visually assessed and further confirmed by PCR analyses according to Harper et al.³². PCR analyses showed that all trees, sampled according to Tatulli et al.⁷, resulted infected by X. fastidiosa subsp. pauca. We declare that we have the permission to collect leaves samples according to a specific agreement between Invaio Sciences (D.V.) and the orchard owner. The samples were collected in accordance with relevant institutional, national, and international guidelines and legislation. The formal identification of the plant material was assessed by Marco Scortichini (M.S.) from the olive orchard structure records supplied by the farmer and confirmed by pomological characterization³³. Voucher samples of the lyophilized studied plant material are available from the authors (F.P.F.).