Plant growth-promoting traits and biocontrol mechanism of three Pseudomonas strains against Geotrichum citri-aurantii

Background Plant growth-promoting rhizobacteria (PGPR) play essential roles in improving plant growth performance and enhancing plant disease resistance. Pseudomonas species are widely recognized as promising beneficial microorganisms owing to their excellent plant growth-promoting and biocontrol potential. Methods Three bacterial strains, MBJ003, MBJ016 and MB1046, were isolated from potato and tomato rhizosphere soils collected in Guangdong Province, P.R. China. Taxonomic identification was performed based on morphological characteristics, physiological and biochemical profiles, as well as phylogenetic and whole-genome analyses. Genomic features, plant-growth promoting traits and antifungal activities against Geotrichum citri-aurantii were characterized, and the function of the type VI secretion system (T6SS) in strain MB1046 was explored. Results Strain MBJ003 was identified as Pseudomonas paraeruginosa , MB1046 as Pseudomonas palmensis , and MBJ016 represents a novel Pseudomonas species. Whole-genome sequencing uncovered abundant and diverse secondary metabolite biosynthetic gene clusters (BGCs) underlying biocontrol capacity. Additionally, strain MB1046 harbours 17 type VI secretion system (T6SS) components. All three strains exhibited multiple plant-beneficial traits including phosphate solubilization, siderophore synthesis and IAA production, while strain MBJ003 additionally showed protease activity. The three strains displayed strong antagonism toward G. citri-aurantii . Their cell-free fermentation supernatants exerted antifungal effects, with MBJ003 showing the strongest inhibition. In vitro inoculation assays confirmed that these strains effectively control citrus postharvest disease caused by G. citri-aurantii . We further provided insights into the T6SS-mediated antagonism of MB1046 against G. citri-aurantii . Conclusion This study systematically characterizes the plant-growth-promoting properties and antifungal mechanism of three Pseudomonas strains. These strains are valuable microbial candidates for developing biocontrol agents to manage crop postharvest diseases.