Biocontrol of Sclerotinia sclerotiorum and plant growth promotion in common bean (Phaseolus vulgaris L.) by Bacillus spp.

Abstract White mold, caused by Sclerotinia sclerotiorum , is one of the most important diseases affecting common bean crops. Due to its global distribution and wide host range, the persistence of S. sclerotiorum in the environment is favored by the formation of survival structures, which complicates control measures. In this context, biological control emerges as a sustainable strategy for pathogen suppression and plant growth promotion. To explore this approach, nine strains of Bacillus spp. were screened for their ability to control S. sclerotiorum strain SSF and promote growth of common bean ( Phaseolus vulgaris L.) plants. All strains exhibited antagonistic activity against S. sclerotiorum strain SSF, demonstrated through in vitro antagonism assays, including dual culture and cell-free supernatant (CFS) tests, and volatile organic compounds (VOCs) exposure, indicating the involvement of multiple antagonistic mechanisms. In addition, the strains displayed key in vitro biocontrol traits, such as the production of cell wall–degrading enzymes and siderophores. Greenhouse trials confirmed the efficacy of selected strains in controlling white mold and promoting bean plant growth. Isolates EVSA, BERA II, and BEFA I stood out by enabling the survival of plants inoculated with S. sclerotiorum while not impairing seed germination. Both bacterial co-inoculation (EVSA, BERA II, and BEFA I) and the EVSA strain alone promoted shoot and root development in bean plants. EVSA demonstrated multifunctional activity, combining effective suppression of S. sclerotiorum strain SSF with plant growth promotion, positioning it as a promising candidate for bioinoculant development in the sustainable management of white mold.