Ten Challenges to Understanding and Managing the Insect-Transmitted, Xylem-Limited Bacterial Pathogen Xylella fastidiosa

Beyond Xylella, Integrated Management Strategies for Mitigating Xylella fastidiosa Impact in Europe (BeXyl) (Grant Agreement 101060593). Partner/Coordinador principal: Blanca B. Landa del Castillo, Investigadora Científica del Instituto de Agricultura Sostenible (IAS-CSIC).

An unprecedented plant health emergency in olives has been registered over the last decade in Italy, arguably more severe than what occurred repeatedly in grapes in the United States in the last 140 years. These emergencies are epidemics caused by a stealthy pathogen, the xylem-limited, insect-transmitted bacterium Xylella fastidiosa. Although these epidemics spurred research that answered many questions about the biology and management of this pathogen, many gaps in knowledge remain. For this review, we set out to represent both the U.S. and European perspectives on the most pressing challenges that need to be addressed. These are presented in 10 sections that we hope will stimulate discussion and interdisciplinary research. We reviewed intrinsic problems that arise from the fastidious growth of X. fastidiosa, the lack of specificity for insect transmission, and the economic and social importance of perennial mature woody plant hosts. Epidemiological models and predictions of pathogen establishment and disease expansion, vital for preparedness, are based on very limited data. Most of the current knowledge has been gathered from a few pathosystems, whereas several hundred remain to be studied, probably including those that will become the center of the next epidemic. Unfortunately, aspects of a particular pathosystem are not always transferable to others. We recommend diversification of research topics of both fundamental and applied nature addressing multiple pathosystems. Increasing preparedness through knowledge acquisition is the best strategy to anticipate and manage diseases caused by this pathogen, described as "the most dangerous plant bacterium known worldwide."

Support was provided by a fellowship from the OECD Cooperative Research Programme: Sustainable Agricultural and Food Systems in 2020 (completed in 2022/2023 while writing this article) awarded to L. De La Fuente; the California Department of Food and Agriculture, Pierce's Disease-Glassy Winged Sharpshooter (grant 21-0270-000-SA awarded to L. De La Fuente); the Alabama Agricultural Experiment Station Hatch Grant awarded to L. De La Fuente; the European Union's Horizon Action Programme “Food, Bioeconomy Natural Resources, Agriculture and Environment” Project BeXyl (Beyond Xylella, Integrated Management Strategies for Mitigating Xylella fastidiosa impact in Europe; grant 101060593); MCIN/AEI/10.13039/501100011033 (project PID2020-114917RB-100 Proyectos I+D+i Retos Investigación awarded to J. A. Navas-Cortés and B. B. Landa); MICIU/AEI/10.13039/501100011033 “Unión Europea Next Generation EU/PRTR” (Project TED2021-130110B-C41 Proyectos Estratégicos Orientados la Transición Ecológica y a la Transición Digital awarded to B. B. Landa); and Junta de Andalucía, Spain, Qualifica Project (QUAL21-023 IAS awarded to IAS-CSIC).

Peer reviewed