Predictive studies are essential to establish fundamental data for monitoring and controlling Xylella fastidiosa infections in our country. Limited knowledge exists about how Xylella fastidiosa interacts with the plant host's immune system, leaving numerous unanswered questions regarding Xylella fastidiosa biology and its interactions with national plant hosts. Key inquiries include understanding of how the plant immune system interfaces with Xylella fastidiosa in the xylem and identifying the specific or shared mechanisms underlying the susceptibility of different hosts. Factors such as the presence of insect vectors, abundance of host plants, and climate suitability play pivotal roles in Xylella fastidiosa dispersal. We recommend that countries identified with relatively high risk, like Portugal, undertake thorough individual risk analyses. The implementation of preventive measures and, if necessary, the enhancement of surveillance systems for early detection of Xylella fastidiosa in plants and insect vectors are crucial steps. Additionally, raising awareness is of equal importance to mitigate socioeconomic and ecological impacts on their ecosystems.

Xylella fastidiosa (Xf) is classified as a quarantine pest due to its consequences on economically significant crops. Its main form of transmission in Europe is through the insect Philaenus spumarius. Due to climate change, populations of insect vectors became more extensive, resulting in the dissemination of the bacteria through longer periods, but destruction of these insects raises issues, due to their role in nature. Upon infection, Xf causes the occlusion of xylem vessels by bacterial aggregates, and tylosis production by the plant as a response to infection. Although symptomatic manifestations of Xf are often linked to water stress, a variety of plant species have been found to carry the pathogen without symptoms, making it all too easy to evade detection when relying on visual inspections. Beyond water stress, other conditions (individual plant resistance/tolerance, bacterial concentrations, transpiration rates, and interactions between subspecies) may be implicated in symptom development. A thorough understanding of how this disease develops, especially its capacity to spread from the initial focus and establish a systemic infection, is imperative. This review focuses on the Xf infection process, the development of symptoms, its spread within Portugal, and the actions that have been taken to counter it.