Isolation and Identification of Endophytic Bacterium B5 from Mentha haplocalyx Briq. and Its Biocontrol Mechanisms Against Alternaria alternata-Induced Tobacco Brown Spot

Summary

Scientists discovered a beneficial bacterium called Bacillus velezensis in mint plants that can fight tobacco brown spot disease caused by a fungus. This bacterium works by producing natural antifungal compounds and enzymes that damage the fungus, and it helps boost the plant’s own defense systems. In greenhouse tests, this bacterial treatment was as effective as commercial chemical fungicides, offering farmers a safer, more environmentally friendly option for protecting their tobacco crops.

Background

Tobacco brown spot disease caused by Alternaria alternata poses significant threats to tobacco production. Chemical fungicides have drawbacks including resistance development and environmental concerns. Endophytic bacteria from medicinal plants represent promising biocontrol alternatives.

Objective

To isolate and identify endophytic bacterial strains from Mentha haplocalyx with antifungal activity against A. alternata and characterize their biocontrol mechanisms for tobacco brown spot disease management.

Results

Strain B5 was identified as Bacillus velezensis with 82.76% inhibition against A. alternata and broad-spectrum activity (66.34-87.23%) against six pathogenic fungi. B5 produces cell wall-degrading enzymes, siderophores, and IAA. Greenhouse trials showed 60.66% relative control efficacy comparable to difenoconazole fungicide.

Conclusion

B. velezensis B5 demonstrates significant biocontrol potential against tobacco brown spot disease through multiple antagonistic mechanisms including enzyme production, secondary metabolite synthesis, and plant defense enzyme activation. This strain serves as a safe, effective alternative to chemical fungicides for sustainable disease management.
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