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Xylella May Not Be Responsible for Olive Tree Devastation in Puglia, Study Finds

New research suggests that Xylella fastidiosa was responsible for just a small percentage of the olive trees destroyed by Olive Quick Decline Syndrome (OQDS) in Puglia.

For more than a decade, the prevailing wisdom had been that the Xylella fastidiosa (Xf) bacterium infected olive trees across the southern Italian region, resulting in the deadly OQDS.

However, research published in the Journal of Phytopathology found that slightly less than 23 percent of trees killed by OQDS from February 2016 to May 2017 were infected by Xf.

Between May 2021 and February 2022, slightly more than three percent of the OQDS-affected olive trees were found to carry Xylella.

If confirmed – and some scientists are skeptical – the findings imply that the strategies currently employed to contain Xf may not effectively address the spread of OQDS.

Researchers said the conclusions are based on data gathered by regional phytosanitary bodies and research institutions from 2013 to 2023.

The data include the areas monitored, the number of trees exhibiting OQDS symptoms, the number of plants examined, the number of trees testing positive for Xylella fastidiosa pauca – a strain of the bacteria that infects olive trees – and the number of plants uprooted within the designated zones in Puglia.

“Everything we wrote comes from reading those numbers,” said Marco Scortichini, lead olive and fruit crop researcher at the Italian Council for Agricultural Research and Economics (CREA), who co-authored the study.

Current methods for detecting Xylella fastidiosa have advanced, including trained dogs and drones.

“These techniques have simplified the detection of Xylella fastidiosa compared to earlier methods,” Scortichini said. “Significant research investment in recent years has led to the development of effective and highly sensitive tools.”

Local inspectors are responsible for the monitoring tasks, selecting olive trees for sampling by specialized labs to detect Xylella fastidiosa’s presence.

“Expectations might suggest a high prevalence of Xylella fastidiosa in olive trees from infected zones,” Scortichini said. “Yet, we find ourselves at a mere 3.21 percent.”

Since its discovery in Apulian olive trees in 2013, Xylella fastidiosa has been under intense scrutiny by both regional and national authorities.

The bacterium is classified as a List-A quarantine pathogen, indicating it was previously unidentified in the region and has caused significant damage in other areas, including the Americas. More