Biocontrol Potential of Three Bacterial Strains, Isolated from Vermicompost, Against Pre-Emergence Damping-Off of Tomato Caused by Rhizoctonia solani, Under Laboratory and Greenhouse Conditions

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 contrast, during vermicomposting, earthworms generate numerous beneficial outcomes. This study aimed to screen antagonistic bacteria found after vermicomposting for their potential to inhibit the pre-emergence damping-off of tomato seedlings caused by <i>Rhizoctonia solani</i>. Using a dual culture method, 85 bacterial isolates were screened, three of which demonstrated antagonistic activity against <i>R. solani</i>. Molecular characterization based on 16S ribosomal RNA identified the bacterial isolates as <i>Bacillus subtilis</i> (NOAC.B77), <i>Bacillus vallismortis</i> (NOAC.B42), and <i>Bacillus cereus</i> (NOAC.B17). The strains NOAC.B77 and NOAC.B42 exhibited the most significant inhibitory effects on the mycelial growth of <i>R. solani</i>, with inhibition levels of 80.8% and 79.2%, respectively. In greenhouse trials, only 13% of the Inoculated, Unprotected Control tomato seedlings emerged, i.e., the <i>R. solani</i> inoculum caused an 87% level of preemergence damping off. In contrast, after treatment with the bacterial strains NOAC.B77 and NOAC.B42, tomato seedling emergence was not significantly different from the Uninoculated 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.