Salicaceae endophytes in a context of Xylella fastidiosa and Brenneria salicis infection
(2026)
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- (en) Vascular pathogens cause some of the most damaging diseases in crops and woody perennials. Among them, Xylella fastidiosa and Brenneria salicis are European quarantine bacteria that colonize xylem tissues, where they may persist asymptomatically or cause severe disease outbreaks. In this context, this thesis characterizes the xylem-associated bacterial microbiome of Salicaceae and investigates its functional role in interactions with vascular pathogens. Using complementary culture-dependent and metabarcoding approaches, more than 400 bacterial endophytes belonging to 43 genera and 104 species were isolated from willow and poplar xylem sap, while 16S rRNA amplicon sequencing revealed a broader community spanning 158 genera and enabled the identification of a core xylem microbiome dominated by Bacillus spp. Functional screening showed that several isolates exhibited antagonistic activity against X. fastidiosa, B. salicis, and major vascular fungi. A subset of strains, mainly belonging to Bacillus, Pseudomonas, and Erwinia, was selected for further analyses, together with the reference biocontrol strain Paraburkholderia phytofirmans PsJN. Genome mining revealed diverse biosynthetic gene clusters, plant growth–promoting traits, and a low virulence potential, supporting their suitability as biocontrol candidates. In planta co-inoculation experiments in tobacco and willow demonstrated that selected endophytes could colonize xylem tissues and stimulate plant growth. In tobacco, co-inoculation was associated with trends toward reduced pathogen loads and partial mitigation of disease symptoms, while in willow, selected endophytes were associated with a mitigation of visual disease symptoms. Altogether, this work provides a pioneering framework positioning the xylem microbiome as a functional ecological buffer capable of limiting pathogen-driven dysbiosis and opens new avenues for microbiome-based strategies to manage vascular diseases in woody plants.
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Pesenti, L. (2026). Salicaceae endophytes in a context of Xylella fastidiosa and Brenneria salicis infection. https://hdl.handle.net/2078.5/276398