Increasing pressure from xylem-limited pathogens has driven the search for beneficial xylem-inhabiting endophytes that can enhance growth, stress tolerance, and disease resistance in woody plants. This study characterized the culturable xylem microbiota of Salicaceae species (willow and poplar) and evaluated their potential as biological control agents against vascular pathogens. A combination of microbial isolation, metabarcoding, and whole-genome sequencing was used to characterize xylem-associated bacteria. Functional traits were assessed through in vitro assays, while genome mining identified genes linked to plant-beneficial activities. Interactions between endophytes and pathogens were tested using fluorescently labeled strains in tobacco (Nicotiana tabacum) and in vitro-grown willow (Salix caprea). Bacterial genera (Bacillus, Pseudomonas, Erwinia) exhibited plant growth-promoting traits and strong antagonism against bacterial and fungal vascular pathogens, including Xylella fastidiosa, Brenneria salicis, Fusarium spp., and Verticillium dahliae. Genome analyses revealed functions related to nutrient acquisition, biofilm formation, and antimicrobial production. Co-inoculation assays significantly reduced pathogen load and disease symptoms in tobacco and mitigated symptoms in willow. Xylem endophytes act as context-dependent allies in woody plant defence. This study provides a functional and genomic framework supporting microbiome-based strategies to enhance resistance against vascular pathogens in long-lived woody hosts.
Pesenti et al. (Wed,) studied this question.