Molecular characterization and antagonistic activity of Bacillus strains against Sclerotium rolfsii

The devastating soil-borne pathogen Sclerotium rolfsii has become increasingly significant worldwide, affecting several crops. However, biological disease management, particularly using antagonistic microbes, offers an environmentally friendly alternative to chemical control. Bacillus species, in particular, have demonstrated strong antagonistic potential against various fungal pathogens. In this study, the morpho-microscopic and biochemical characterization of Bacillus isolates obtained from rhizosphere soil was conducted. Furthermore, their antagonistic activities were assessed in vitro using dual culture and well diffusion techniques against S. rolfsii. During primary screening, four isolates viz. S3C9, S1C9, S2C9, and S6C8 strongly suppressed fungal mycelial growth, with inhibition zones measuring 18.3, 14.7, 14.3, and 14.7 mm, respectively. Three isolates (S2C9, S3C9, and S4C9) were further evaluated for inhibitory properties using cell-free supernatant through the well diffusion method, yielding inhibition zones of 6.3, 4.7, and 4.7 mm, respectively. Moreover, molecular analysis identified two isolates, S1C9 and S3C9, as strains of Bacillus subtilis, with GenBank accession codes OP962345 and OQ180051, respectively. This study provides evidence that the local soil of Kot Diji, Sindh Province, Pakistan, harbors beneficial microbes with significant antifungal activity, which could be utilized for future biocontrol strategies against phytopathogenic fungi.