The endophytic bacterium Bacillus subtilis R8 as a prospective biocontrol agent for managing tea blister blight and enhancing tea yield

Blister blight, caused by the fungus Exobasidium vexans, is a major disease affecting tea plants. This study aimed to isolate and evaluate the efficacy of endophytic bacterial strains as potential biocontrol agents against the disease. Thirteen endophytic bacterial strains were isolated from healthy tea plants collected in Thach That, Hanoi, Vietnam. Six of these strains exhibited antagonistic effects against E. vexans, with strains R8 and S2 showing the highest inhibition. Heat-treated bacterial supernatants lost their antifungal activity, indicating that the inhibitory compounds were protein-based. Strain R8, identified as Bacillus subtilis, also demonstrated plant growth-promoting traits, including the production of Indole-3-acetic acid (IAA) and phosphate solubilization. Greenhouse trials showed that both chemical fungicides and antagonistic bacteria significantly reduced disease incidence, with the preventative application of chemical fungicide being the most effective (control efficacy of about 91.05%), followed by preventative inoculation with antagonistic bacteria (82.77%). Additionally, treated plots yielded significantly more fresh tea shoots, with an increase of 19.02% and 21.17% for antagonistic bacteria and chemical fungicide treatments, respectively, compared to the control. These findings suggest that B. subtilis R8 holds promise as a biocontrol agent, providing both disease suppression and yield enhancement in tea cultivation.