Overgrafting as solution to save old olives and testing germplasm

An extensive trial, consisting of overgrafting 12,5 hectares in 3 private olive orchards (located in the infected area of Salento, in Presicce and Ugento) with 2 different levels of symptom's expression, started in April 2016 and completed in the spring 2017 without public funding, is presented. With the collaboration of germplasm collections, scientific institutions and consortia, 260 among different cvs and clones, representative of 19 olive growing countries and all Italian regions, were collected and grafted, by patch grafting, using a complete randomized scheme with 5 replicates and 3 controls on each plants (the susceptible cv Ogliarola salentina and 2 resistant Leccino and Frantoio). Starting from the observation, in the oldest heavily infected area, of almost asymptomatic plants where Leccino were grafted over 10 years ago on trunk of susceptible cvs, the experimental idea has several objectives: try to save the centenary trees by substituting the canopy with resistant varieties; define a grafting protocol adapted to the local conditions; develop a new method "Xylella Quick Tolerance Test" aimed to evaluate the susceptibility of a large quantity of germplasm in shorter time; c. identify a larger number of resistant/tolerant cvs and sources of resistance; d. estimate the potential risk of spreading of the OQD disease in other territories. Due to the good engraftment % and development of grafts the first preliminary evidences are expected in the present growing season.