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In a previous study, we isolated four antagonistic bacterial strains viz., Pseudomonas aeruginosa B1-SQU, Pseudomonas indica B2-SQU, Serratia marcescens B3-SQU and Pseudomonas brenneri B4-SQU from the rhizosphere of cabbage which suppressed damping-off in cabbage caused by Pythium aphanidermatum. In this study, potential of these bacterial isolates to produce antimicrobial volatile organic compounds (VOCs) against P. aphanidermatum was tested. The results of the two-sealed-base-plates assay revealed that all four bacterial strains produced VOCs against P. aphanidermatum with the maximum inhibition with P. brenneri B4-SQU followed by S. marcescens B3-SQU, P. aeruginosa B1-SQU and P. indica B2-SQU. Solid-phase microextraction coupled with gas chromatography-mass spectrometry was used to profile the VOCs of bacteria. A total of 20 VOCs were detected in P. aeruginosa B1-SQU and the major compounds identified were Carbon dioxide, 1-Butanol, 3-methyl- and Disulfide, dimethyl. The main volatile compounds detected in P. indica B2-SQU were 1-Butanol, 3-methyl-, Disulfide, dimethyl and 1,2-Propanediamine. Disulfide, dimethyl and 1,2-Propanediamine were the predominant compounds identified in S. marcescens B3-SQU among others. The major compounds detected in P. brenneri B4-SQU were 1-Butanol, 3-methyl-, 1,2-Propanediamine and Disulfide, dimethyl. Dimethyl disulfide, a well-known antimicrobial compound, was detected in the volatile profiles of all four antagonistic bacterial isolates. These results suggest that VOCs of antagonistic bacteria may be involved in the suppression of P. aphanidermatum and these antagonistic bacterial strains may be used as biofumigants for controlling damping-off of cucumber.
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