Investigating an inexplicable decline of olive trees in Puglia, Italy, in Autumn 2013, a team of researchers from the IPSP-CNR of Bari tested some plants for Xylella fastidiosa. And, for the first time in Europe, they found it. Donato Boscia (DB) and Maria Saponari (MS) of the IPSP-CNR were part of that team. Ten years after, we asked them about the Xf spread in Puglia and the evolution of the EU research on the pathogen from the onset to the BeXyl Project. The interview outline reflects the order of the speeches that Donato Boscia and Maria Saponari will deliver at the debate Emergenza Xylella, la Scienza al Centro delle soluzioni (Xylella Emergency, Science at the Center of Solutions) which will take place in Bari on 16 March 2023, on the occasion of the 100th anniversary of the CNR.

Until 2013 the EU was officially a Xylella-free territory. How did you have the idea to test olive trees for Xf?

DB: The idea, or rather, the intuition, came from our mentor, the late Professor Giovanni Martelli – he passed away in January 2020 – who, despite having been retired for some time, continued to attend our laboratories every day. As part of the daily discussions we had with him to hypothesize the possible cause of the olive quick decline, one day he told us “the symptoms and way of spreading remind me of the Pierce’s disease of California vineyards”.

That is a disease caused by Xylella fastidiosa. Correct?

DB: Correct. It was the morning of 11 September 2013. I still keep the email that he sent to his friend and colleague at UC Davis, Doctor Jerry Uyemoto, asking him for more information on Xylella in olive trees.

What are the feelings that you remember of that period? 

DB: We were excited by the full participation into a research activity which, for us phytopathologists, represented a great challenge. We were also aware that this kind of involvement might have caused considerable problems, even personal ones, as it unfortunately occurred. We were concerned by the lack of specific knowledge on the Puglia strain of the bacterium, and by the potential rapid and disastrous evolution of the epidemic. Sad to say, the facts tell us that we were not wrong.

What is the current situation on the ground in Puglia?

DB: The bacterium has now devastated a large part of the Salento peninsula, from Brindisi downwards and it has spread further north patchily, up to the first municipalities of the province of Bari and the borders of the city of Taranto. The territory demarcated as “infected” corresponds to 40% of the region, a hundred times larger than that already affected at the end of 2013. The destroyed or seriously compromised olive trees are several million. A couple of millions of them have been already replaced by new ones of the two cultivars with characters of resistance, Leccino and FS-17.

Any improvement?

DB: There are encouraging signals that indicate a significant slowdown in further diffusion and which is due to various causes, including the better organization and more rapid application of the containment measures implemented by the phytosanitary authorities.

Which has been the role for the European Union in supporting research?

MS: In 2013 there was no established specific research program targeting this pathogen in Europe and in the Mediterranean countries. So, when we first diagnosed the pathogen, we immediately contacted researchers in United States where fully dedicated research units were working on different aspects of Xylella since 1950s. However, despite the relevant knowledge and background gained and shared by the colleagues from the American countries, it was clear that we needed in-depth investigations on the specific epidemiological characteristics of the European outbreaks.

And here comes the EU…

MS: The EU phytosanitary authorities have been very alert, perceiving the threat posed by Xf and the need for an accurate pest risk assessment and science-based containment strategies. From the onset, the EU promoted investments supporting science to fight the phytosanitary emergence.

Which are the outcomes?

MS: Thanks to those investments, a European research network is currently leading the international research on Xylella. The results of the EU supported studies contributed to numerous legislative acts, helping to shape a management strategy tailored on the specific attributes of the EU outbreaks. Having built the basic knowledge, now research itself can spotlight practical solutions to counteract the impact of the bacterial infections. That is the main focus of the ongoing European projects such as BeXyl.

Could you make examples of the new BeXyl approach?

MS: In BeXyl, researchers will develop, for the first time, olive breeding programs and a genetic linkage map for the identification of candidate genes for resistance to Xylella. Indeed, the project involves botanical gardens and will set up sentinel plots in different countries taking into account different bacterial strains, climatic conditions and host species, to expedite the collection of epidemiological information. BeXyl is working closely with BioVexo, to test bio-based products against the bacterium (exploring for example, like for human diseases, synthetic microbial communities to be transplanted in young trees) and to control the vector population.