Scientists from the EU-funded BeXyl project advanced research on the biological and environmental drivers shaping the emergence and spread of Xylella fastidiosa (Xf) in Europe, providing new knowledge and tools to improve preparedness against current and future outbreaks.
Context
Since its first detection in Europe in 2013, the plant pathogen Xylella fastidiosa (Xf) has continued to spread across several Mediterranean regions, raising concerns about its long-term environmental and economic impact.
The BeXyl project has investigated how host plants, bacterial strains, insect vectors, environmental conditions and climate interact to drive epidemics in Europe and neighbouring regions, using these findings to improve surveillance, outbreak management and prevent new introductions of the pathogen.
A major contribution of the project has been the integration of field surveys, sentinel plots, botanical garden surveillance, molecular diagnostics, remote and proximal sensing, and mathematical modelling to support earlier detection and more targeted surveillance.
Host range and pathogenicity
BeXyl has substantially expanded current knowledge on the host range and pathogenicity of European and international Xf strains under both field and controlled conditions. Sentinel monitoring activities in Europe, North and South America, and Central America in the field and natural landscapes, sentinel plots and botanical gardens identified Xf infections across a wide range of ornamental, forestry, and native plant species.
Sentinel plots were established in Brazil, Costa Rica, Portugal, and Spain, Italy, France, Argentina, and the United States. These plots include representative host species such as olive, almond, citrus, grapevine, and Spartium junceum, and are monitored through standardised visual inspections, tissue sampling, and molecular testing. In parallel, BeXyl coordinated surveillance in ex situ collections through botanical gardens in Brazil, Ecuador, Guatemala, and Colombia. These collections are particularly valuable for early warning because they include diverse native, ornamental, and exotic species, including plants that may remain asymptomatic while acting as reservoirs or indicators of new host-pathogen associations.
The project also generated important findings on the susceptibility of Mediterranean crops, forest trees, shrub species and ornamentals to different Xf strains. Under controlled conditions, BeXyl partners inoculated a genetically diverse collection of Xf strains into major crops such as grapevine, olive and almond, as well as blueberry, cherry, hazel, forest species and Mediterranean shrubland plants. These experiments showed that host response depends strongly on the plant species, cultivar, bacterial subspecies, sequence type and strain, confirming that Xf risk must be assessed through specific host–pathogen combinations rather than at plant species level alone.
All these studies demonstrated that several European Xf strains can infect previously unreported Mediterranean hosts, such as Helichrysum italicum (Italian strawflower) by Xf subsp. fastidiosa. Field and sentinel surveillance also detected Xf in additional hosts and countries, including Ficus carica, Fraxinus excelsior, Nerium oleander and Hibiscus × rosa-sinensis, while botanical garden surveys detected Xf DNA in new plant species and revealed previously undescribed Xf genetic variants.
Outbreaks and epidemics on the ground
BeXyl researchers conducted extensive field and landscape surveys to investigate how Xf epidemics emerge and spread under real natural outbreak conditions.
In Mallorca, Spain, analyses of the ongoing outbreak and identified a high diversity of co-occurring subspecies and mixed infections within the same area. The simultaneous presence of different Xf subspecies highlights the need for continued monitoring, particularly because possible genetic recombination events and the emergence of new variants adapted to European conditions.
In Apulia, Italy, new outbreaks identified in 2024–2025 revealed the presence of two new strains, Xf subsp. fastidiosa ST1 in grapevines and Xf subsp. multiplex ST26 in almonds. Surveys confirmed active vine-to-vine spread associated with Pierce’s Disease symptoms, while greenhouse inoculation experiments showed differences in susceptibility among grapevine cultivars.
The project also identified new epidemiological risks linked to insect vectors in the Mediterranean region. In Israel, scientists reported the leafhopper Mesoptyelus impictifrons as a potential new vector species associated with Pierce’s Disease outbreaks in vineyards.
Meanwhile, large-scale surveys conducted in Costa Rica and Argentina further expanded knowledge on Xf distribution, vector biodiversity, and pathogen reservoirs across different agroecosystems.
Climate change and future epidemic risks
Experimental studies also investigated how temperature, atmospheric CO₂ concentrations and water availability influence plant response and disease severity. Trials conducted on grapevine cultivars infected with Xf subsp. fastidiosa ST1 showed that disease severity increased under higher climate change scenarios of combined temperatures and elevated CO₂.
To understand how climate change may influence the establishment and spread of Xf in Europe, BeXyl researchers are developing Species Distribution Models and epidemiological simulations that integrate climate variables, pathogen occurrence data, and ecological niche information. These models are being used to identify areas where environmental conditions may be favourable for Xf establishment under current and future climate scenarios.
These findings provide important evidence that climate change could modify future epidemic risks in several Mediterranean production systems, reinforcing the need for preventive monitoring and adaptive management strategies.
Genomics and adaptation of European strains
BeXyl researchers sequenced and analysed dozens of complete genomes from Europe, the Americas, and other regions to investigate the evolutionary history, introduction pathways, and adaptive traits of different Xf subspecies.
Genomic analyses revealed that the recent outbreak of Xf subsp. fastidiosa ST1 in Portugal likely originated from California around 2020. Other studies reconstructed historical introductions of the pathogen into the United States and identified genetic changes associated with adaptation to grapevine hosts.
The project also explored genetic traits potentially linked to host specificity, biofilm formation, natural competence, and climate adaptation. In addition, global genomic data mining revealed extensive hidden diversity within the genus Xylella, including previously unknown lineages.
Together, these results contribute to a deeper understanding of how Xf moves, diversify and adapts to new hosts and environments, supporting the development of more robust risk assessment frameworks for Europe.
Preparedness in Europe
The findings generated by BeXyl support the development of improved surveillance systems, predictive risk maps and evidence-based management strategies for Xf in Europe, providing plant health authorities and policy-makers with reliable knowledge and tools to better anticipate future outbreaks and reduce the impact of this pathogen on European agriculture, landscapes and natural ecosystems.
Xylella fastidiosa
Xylella fastidiosa is one of the most threatening plant pathogens worldwide, capable to infect more than 700 plant species. It causes diseases responsible for severe agricultural and environmental losses in several regions of the world. Since its first detection in the European Union in 2013 on olive trees in southern Italy, outbreaks have also been reported in France, Spain, Portugal, and other Mediterranean areas.
For more information: European Food Safety Authority – Xylella fastidiosa
Fonte: BeXyl – Beyond Xylella
