Italian Researchers Report Progress in Search for Xylella-Resistant Olive Trees

New breeding programs, genomic research and field trials in Italy are offering fresh hope in the fight against Xylella fastidiosa.

More than a decade after the bacterium began transforming the landscape of southern Puglia, Italy’s scientific community is reporting results that offer cautious optimism. A growing set of tools could help rebuild olive cultivation in the country’s hardest-hit region.

There are no shortcuts or miracle solutions against Xylella. The answer lies in a multidisciplinary approach that brings together research, innovation and scientific expertise.– Andrea Rocchi, president, Council for Agricultural Research and Economics (CREA)

Despite the loss of more than 21 million olive trees since Xylella fastidiosa was first identified in Puglia, and the continued detection of new infections, Puglia remains Italy’s largest olive oil-producing region.

In recent weeks, Italian researchers presented progress from several projects funded under the country’s Extraordinary Plan for Olive-Growing Regeneration in Puglia.

Along with the recent appointment of a national commissioner to improve coordination of Italy’s response to Xylella fastidiosa, the projects signal a gradual shift from emergency management toward the long-term recovery of olive cultivation.

One area of investigation combines olive breeding with sustainable agronomic management. Through the Genforagris project, coordinated by the Council for Agricultural Research and Economics (CREA), researchers aim to select new genetic material that combines resilience to the bacterium with productivity, olive oil quality and adaptation to increasingly challenging environmental conditions.

Rather than relying solely on controlled experimental conditions, researchers are evaluating candidate genotypes in the heart of the infected area of Salento.

“The genetic material used in the project consists of cloned seedlings obtained from different inter-varietal crosses,” Samanta Zelasco, the project’s coordinator at CREA, told Olive Oil Times. “For more than nine years, these plants have been growing in an experimental orchard located in the heart of the area infected by Xylella fastidiosa, where they have been exposed to high infection pressure.”

The plants are monitored twice a year, in April and November, using molecular tests conducted in accordance with internationally recognized diagnostic protocols developed by the European and Mediterranean Plant Protection Organization.

Zelasco said the candidate genotypes are also evaluated for characteristics beyond their response to Xylella, including vegetative growth, productivity and resilience to drought and other pathogens affecting olive cultivation.

“Among the genotypes under selection, some have shown excellent adaptability and good resistance to environmental stresses and/or pathogens, including peacock spot, cercosporiosis and olive knot, as well as to the olive fruit fly,” she said.

Zelasco added that researchers are also assessing the quality of the olive oil produced by the genotypes.

CREA researchers recently announced that approximately 30 olive genotypes had been identified with reduced bacterial presence, including nine in which no bacterial load was detected. However, Zelasco cautioned against interpreting the finding as evidence that those nine genotypes are necessarily the most promising.

“I deliberately did not emphasize the nine genotypes without detectable bacterial load,” she said. “They may simply not have become infected yet, or the bacterial concentration may still be below the detection threshold. During three years of monitoring, we have seen genotypes that were initially completely negative later become positive.”

Instead, researchers are placing greater emphasis on genotypes that consistently maintain very low bacterial populations over time.

“The genotypes with very low bacterial loads have proved remarkably stable throughout the monitoring period,” Zelasco said. “These are the ones we consider particularly promising.”

Beyond genetic selection, Genforagris is investigating agronomic practices intended to restore soil fertility and improve the long-term sustainability of olive production in Salento, where the bacterium was first detected.

Among the approaches being tested is the return of olive industry by-products to the soil through on-farm composting. Researchers said the practice remains underused despite its recognized benefits for increasing organic matter and improving soil health.

The project’s next phase will focus on propagating the most promising genotypes and establishing new evaluation orchards in different environments.

One of the planned sites is the agricultural program at the Presta-Columella secondary school in Lecce, which is already collaborating with project partners on several experimental activities.

“After the establishment of new experimental fields in different areas, another five to eight years will be needed to obtain reliable answers on the performance of the new genotypes,” Zelasco said.

The trials will help determine whether the selected material consistently combines resistance or tolerance to Xylella with the agronomic characteristics required for commercial cultivation.

While promising, Genforagris is only one component of a broader scientific effort underway in Italy.

Other projects include Novixgen, which has identified more than 200 promising olive genotypes and genetic markers associated with resistance, and Omibreed, which investigates the molecular mechanisms underlying resistance using genomic and multi-omics approaches.

Another initiative, ANCoSIX, is testing antimicrobial peptides, bacteriophages and nanotechnology-based treatments against the pathogen.

“There are no shortcuts or miracle solutions against Xylella. The answer lies in a multidisciplinary approach that brings together research, innovation and scientific expertise,” CREA president Andrea Rocchi said while presenting the institute’s latest results.

For Zelasco, the research remains open-ended.

“There is still much to discover about the interaction between the plant and the pathogen,” she said. “The field we are studying represents an excellent open-air laboratory.”