Mitigation Measures of Quick Decline Syndrome in Ancient and Monumental Olive Trees of Ostuni (Apulia, Italy) Positive to Xylella fastidiosa

The Olive Quick Decline Syndrome (OQDS) in Apulia region, south of Italy, has caused over the last decade the desiccation of about one million olive trees vs. a population of eleven million olive trees in the sub-region of Salento peninsula and an overall sixty-five million olive trees of Apulia. The syndemic nature of this syndrome includes agronomic, societal and biological events, such as the phytopathogenic bacterium Xylella fastidiosa subsp. pauca (Xfp), several phytopathogenic fungi, erratic agronomic management practices, salinization, pollution, erosion, decline of biodiversity, misuse of the territory. Insect vector control of Xf, and eradication of olive trees have proven to be of limited efficacy, while co-existence and mitigation measures are retained more effective. Here an approach is described, applied to thirty-seven monumental olive trees of the municipality of Ostuni, being PCR-positive to Xf in 2021, some showing the syndrome traits. All the trees were in the former containment area and forcedly destined to eradication or pollarding and grafting. In 2024, the same partially pollarded and grafted trees, treated with an agronomic protocol, are healthy, productive and PCR-positive to Xfp. The results suggest that mitigation measures represent an alternative to generalized eradication of olive trees affected by OQDS in containment areas.