Unveiling Nicotiana tabacum L. growth promotion and Fusarium root rot biocontrol by endophytic Bacillus spp. from different hosts

• Endophytic Bacillus spp. are present in a wide range of host plants. • B. subtilis A2M2177 and B. subtilis A2M2295 promote Nicotiana tabacum L. growth. • The two biocontrol agents reduce the occurrence and severity of tobacco root rot. Members of the genus Fusarium are considered to be highly prevalent plant pathogens globally. Utilizing biological control methods is an eco-friendly and cost-effective strategy to manage and mitigate the spread of plant diseases. In this study, 326 bacterial strains were isolated from 20 different hosts, and four selected isolates with high antagonistic activity against F. oxysporum B-9-1 were subsequently assessed in detail. Molecular identification revealed that these strains belong to Bacillus spp. Physiological assays indicated that all strains can produce indole-3-acetic acid (IAA), phosphate solubilization, protease, amylase, and cellulase. However, only two strains, B. subtilis A2M2177 and B. subtilis A2M2295, formed hydrolytic halos attributable to siderophore production. Plant growth promotion experiments showed that Nicotiana tabacum L. seedlings inoculated with B. subtilis A2M2177 and B. subtilis A2M2295 exhibited significantly better growth parameters, including plant height, leaf area, stem width, fresh weight, dry weight, and chlorophyll content. In addition, B. subtilis A2M2177 and B. subtilis A2M295 significantly reduced the occurrence and severity of tobacco root rot in greenhouse experiments. Overall, the results indicate a high potential for the use of B. subtilis A2M2177 and B. subtilis A2M2295 as biocontrol agents and plant growth promoters.