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

Abstract

Giorgio Doveri, Giovanni Pergolese, Emanuela Sardella, Marco Scortichini, Giusto Giovannetti, Michele Saracino, Luigi Botrugno and Marco Nuti

The Olive Quick Decline Syndrome (OQDS) in Apulia region, south of Italy, has affected over the last decade more than 6.5 million of olive trees. The syndemic nature of this syndrome, which includes the phytopathogenic bacterium Xylella fastidiosa (Xf), has caused great difficulties in the control of OQDS, and both the insect vector control of Xf, and eradication of olive trees have proven to be of limited efficacy. In this on-farm case study a co-existence and mitigation approach is described, applied to thirty-eight monumental, or having the traits of monumentality, olive trees of the municipality of Ostuni. They were PCR-positive to Xf in 2021, showing random symptoms of desiccation, and the symptoms of generalized OQDS. The trees were affected by different bacterial and fungal pathogens, nematodes, and pests. These same trees, treated during three consecutive years with an agronomic protocol (Good Agronomic Practices including microbial biostimulants), in 2025 are alive, productive, still PCR-positive to Xf except one, and having milder symptoms associated to the syndrome. The results suggest that mitigation measures, and co-existence with Xf, might represent an alternative to the generalized eradication of olive trees affected by OQDS.

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