Pathotyping Citrus Ornamental Relatives with Xanthomonas citri pv. citri and X. citri pv. aurantifolii Refines Our Understanding of Their Susceptibility to These Pathogens

14 Pág. (This article belongs to the Special Issue Integrating Science on Xanthomonas and Xylella for Integrated Plant Disease Management)
Xanthomonas citri pv. citri (Xcc) and X. citri pv. aurantifolii (Xca) are causal agents of Citrus Bacterial Canker (CBC), a devastating disease that severely affects citrus plants. They are harmful organisms not reported in Europe or the Mediterranean Basin. Host plants are in the Rutaceae family, including the genera Citrus, Poncirus, and Fortunella, and their hybrids. In addition, other genera of ornamental interest are reported as susceptible, but results are not uniform and sometimes incongruent. We evaluated the susceptibility of 32 ornamental accessions of the Rutaceae family belonging to the genera Citrus, Fortunella, Atalantia, Clausena, Eremocitrus, Glycosmis, Microcitrus, Murraya, Casimiroa, Calodendrum, and Aegle, and three hybrids to seven strains of Xcc and Xca. Pathotyping evaluation was assessed by scoring the symptomatic reactions on detached leaves. High variability in symptoms and bacterial population was shown among the different strains in the different hosts, indicative of complex host–pathogen interactions. The results are mostly consistent with past findings, with the few discrepancies probably due to our more complete experimental approach using multiple strains of the pathogen and multiple hosts. Our work supports the need to regulate non-citrus Rutaceae plant introductions into areas, like the EU and Mediterranean, that are currently free of this economically important pathogen.
This research was funded ORPRAMed Project on “Risk assessment of introduction of Xanthomonas citri subsp. citri through commercial trade of ornamental rutaceous plants in the Mediterranean basin”, ERA-NET ARIMNET 2-Call 2015.C.B., V.C. acknowledge the University of Catania for support under the projects “Investigation of phytopathological problems of the main Sicilian productive contexts and eco-sustainable defense strategies” (PIA.CE.RI. 2020–2022 Linea 2-Research Project MEDIT-ECO.); “Emergent Pests and Pathogens and Relative Sustainable Strategies” (Progetto di ricerca di Ateneo 2018-2020). O.P. and I.R. acknowledge the European Union (ERDF, EAFRD) and Réunion regional council for support