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Bacterial wilt disease of tomato (<i>Solanum lycopersicum</i> L.), incited by <i>Ralstonia solanacearum</i> (Smith), is a serious agricultural problem in India. In this investigation, chemical mutagenic agents (NTG and HNO₂ treatment) and ultraviolet (UV) irradiation have been used to enhance the antagonistic property of <i>Bacillus amyloliquefaciens</i> DSBA-11 against <i>R. solanacearum</i> UTT-25 towards an effective management of tomato wilt disease. The investigation established the fact that maximum inhibition to <i>R. solanacearum</i> UTT-25 was exerted by the derivative strain MHNO₂-20 treated with nitrous acid (HNO₂) and then by the derivative strain MNTG-21 treated with NTG. The exertion was significantly higher than that of the parent <i>B. amyloliquefaciens</i> DSBA-11. These two potential derivatives <i>viz</i>. MNTG-21, MHNO₂-20 along with MUV-19, and a wild derivative strain of <i>B. amyloliquefaciens</i> i.e.,DSBA-11 were selected for GC/MS analysis. Through this analysis 18 major compounds were detected. Among the compounds thus detected, the compound 3-isobutyl hexahydropyrrolo (1,2), pyrazine-1,4-dione (4.67%) was at maximum proportion in the variant MHNO₂-20 at higher retention time (RT) of 43.19 s. Bio-efficacy assessment observed a record of minimum intensity (9.28%) in wilt disease and the highest bio-control (88.75%) in derivative strain MHNO₂-20-treated plants after 30 days of inoculation. The derivative strain MHNO₂-20, developed by treating <i>B. amyloliquefaciens</i> with nitrous acid (HNO₂), was therefore found to have a higher bio-efficacy to control bacterial wilt disease of tomato under glasshouse conditions than a wild-type strain.