An Evaluation of Monitoring Surveys of the Quarantine Bacterium Xylella Fastidiosa Performed in Containment and Buffer Areas of Apulia, Southern Italy

Xylella fastidiosa is a quarantine phytopathogen for the European Plant Protection Organization and currently infects olive trees in the Apulia region (southern Italy). Upon the Implementing Decision of the European Union 2016/764 of May 12, 2016, extensive monitoring surveys were performed on approximately 190？000 ha to ascertain the possible occurrence of X. fastidiosa. The primary objectives of the analysis were to start to collect epidemiological data on X. fastidiosa occurrence in areas far from the initial outbreaks and discuss the results of the pathogen detection. A total of 220？279 olive trees were inspected. Basic information on farm and trees management was obtained. A total of 13？706 olive trees were analyzed through serological and molecular techniques to verify the possible occurrence of the bacterium. The cultivars “Nociara,” “Cima di Melfi,” and “Cellina di Nardò” showed the highest occurrence of decline symptoms. Tree age appears to be related to the incidence of decline symptoms. Olive trees growing in well-managed soils showed fewer symptoms than trees cultivated in farms where such agronomic techniques are not regularly performed. X. fastidiosa was detected in 2078 samples taken from symptomatic trees and 1653 samples obtained from asymptomatic trees. In 3300 samples taken from symptomatic trees, the bacterium was not detected. Implementation and utilization of reliable in situ detection techniques could increase the number of sampled trees in each plot, thus allowing a more extensive and robust assessment of X. fastidiosa–infected plants in areas where the pathogen inoculums are still low