Biocontrol Potential of Three Bacterial Strains, Isolated from Vermicompost, Against Rhizoctonia solani on Tomato Under Laboratory and Greenhouse Conditions

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Synthetic chemicals, such as fertilizers and pesticides, are widely used in agriculture to improve soil fertility, and to control weeds, pests and diseases. Numerous studies have highlighted the negative effects of these chemicals on the soil environment. In the process of vermicomposting, earthworms generate numerous beneficial outcomes. This study aimed to screen antagonistic bacteria found after vermicomposting for their potential to inhibit the damping-off of seedlings caused by Rhizoctonia solani. Using a dual culture method, 85 bacterial isolates were screened, three of which demonstrated antagonistic activity against R. solani. Molecular characterization based on 16S ribosomal RNA identified the bacterial isolates as Bacillus subtilis (NOAC.B77), Bacillus vallismortis (NOAC.B42), and Bacillus cereus (NOAC.B17). The strains NOAC.B77 and NOAC.B42 exhibited the most significant inhibitory effects on the mycelial growth of R. solani, with rates of 80.78% and 79.15%, respectively. A comparable pattern was observed under greenhouse conditions, where damping off caused by R. solani was reduced by 55% and 54.33%, respectively. In contrast, only 13% of tomato seeds germinated in the Untreated Control. These results suggest that the bacterial Strains NOAC.B77 and NOAC.B42 could be commercialized as biological agents to control damping-off of tomato seedlings under greenhouse conditions.