Gas chromatography-mass spectrometry analysis of the secondary metabolites produced by Bacillus paramycoides BOK01 and Microbacterium barkeri BPATH02 and investigation of their antifungal activity against tea pathogens.

The present research investigates the chemical profile of secondary metabolites produced by Bacillus paramycoides BOK01 and Microbacterium barkeri BPATH02 rhizospheric bacteria originating from the tea rhizosphere and their antifungal activity against major tea pathogens. GC-MS analysis revealed that dimethyl sulphate (77.09%) was a major compound (Compound I) of B. paramycoides BOK01 and 1H-Purin-6-amine, [(2-fluorophenyl) methyl- (CAS) (Compound II; 16.88%), and docosane (Compound III; 11.75%) as putative major compounds in M. barkeri BPATH02. Furthermore, the ethyl acetate extract of both bacterial antagonists and compounds I, II, and III were evaluated for their efficacy against major tea pathogens, namely Exobasidium vexans, Pseudopestalotiopsis theae, and Fusarium concentricum causing respective blister blight, gray blight, and Fusarium dieback in tea crops using two-sealed-base-plate method. Laboratory screening of ethyl acetate (EA) extracts of both bacterial antagonists at 200 µg/mL provided a 65.95 to 82.5% range of growth inhibition of tested pathogens. At similar dose, compounds I, II, and III provided 70.88 to 77.53%, 67.7 to 78.0% and 71.8 to 73.07% range of growth inhibition of tested pathogens, respectively. Thus, this study shows that bacterial metabolites and their compounds are sources of putative antifungal agents, which can be harnessed for bio-fungicides development against tea diseases.