Colonization of endophytic Bacillus velezensis PEBA20 in eucalyptus and its biocontrol effect against eucalyptus bacterial wilt

BACKGROUND: Eucalyptus bacterial wilt, caused by Ralstonia pseudosolanacearum, is a highly destructive and difficult-to-control vascular disease, primarily because the pathogen invades and occludes host vascular tissues. Exploiting the ability of endophytic biocontrol bacteria to colonize vascular tissues represents a promising strategy for managing this disease. RESULTS: In this study, we investigated the colonization behavior of the endophytic bacterium Bacillus velezensis PEBA20 in eucalyptus and evaluated its biocontrol efficacy against bacterial wilt. Both viable cells and cell-free fermentation filtrates of PEBA20 inhibited the growth of R. pseudosolanacearum, and PEBA20 cells exhibited a clear capacity to occupy and invade pathogen colonies. PEBA20 survived and proliferated in artificial soil, colonized the eucalyptus root surface, including grooves, fissures, and root hairs, and was subsequently detected in root vascular tissues and in stem intercellular spaces and vascular tissues. Detached-branch assays showed that PEBA20 restricted lesion expansion and pathogen accumulation in eucalyptus branches, with a stronger suppressive effect when PEBA20 was inoculated before the pathogen. Pot experiments further demonstrated that PEBA20 application enhanced the activities of defense-related enzymes, including superoxide dismutase, phenylalanine ammonia-lyase, and peroxidase; significantly promoted seedling growth; and achieved 5.0% biocontrol efficacy against eucalyptus bacterial wilt. The field trial further supported the growth-promoting and disease-suppressive potential of PEBA20. CONCLUSION: Collectively, these findings indicate that B. velezensis PEBA20 has a strong capacity for endophytic colonization, disease suppression, and plant growth promotion, providing both a promising bacterial resource and a theoretical basis for the biological control of vascular wilt diseases caused by R. pseudosolanacearum. © 2026 Society of Chemical Industry.