Xylella fastidiosa (Xf) is a xylem-limited, plant-pathogenic bacterium with a wide host range. Processes leading to plant colonization and the specific mechanisms leading to disease are poorly understood yet.

Although a study investigating the mechanisms of host plant specificity experimentally showed that cell-cell signaling-based gene regulation system was associated with host specificity, the target candidate loci could not be identified  and therefore the question remains largely open.

Thus, there is high uncertainty with regard to the potential host range of Xf in the European flora as a wide range of European wild plant species have never been exposed to the bacterium and it is not known whether they would be hosts, and, if so, whether they would develop symptoms.

To this end, the importance of experimental work to determine the host range of pathogens remains paramount to demonstrate that individual genotypes are pathogenic to specific host plant species. Large dataset of genomic sequences will be cooperatively developed within this project, to gather critical elements to understand the evolution of the population in the contaminated areas, and to identify critical parameters involved in Xf-host interaction that could be used to design novel control methods.

Molecular characterization of EU Xf genotypes coupled with biological tests on host range and analysis of ecological parameters will be essential in the development of quarantine, containment, and control practices.