Biocontrol potential of Bacillus strains in interaction with Rhizoctonia solani pathogen of potato

During the growth period, the potato crop is exposed to a combination of biotic and abiotic stresses. Rhizoctonia solani Kuhn is the causal agent of potato stem canker disease and one of the most important soil-borne plant pathogens that reduce the yield and quality of potatoes worldwide. Antagonistic bacteria seem to be a good alternative to chemicals in controlling plant pathogens. This study evaluated the biocontrol properties (hydrolyzing enzymes, siderophore, surfactant, biofilm) of 20 Bacillus isolates against R. solani AG3. In total, 23 to 64.9 % of isolates in dual culture assay, 38.2 to 85.4% in volatile compound production, and 76.9 to 90% in antibiotic production showed inhibition against the tested fungus. The isolates were variable in terms of biocontrol properties. Based on the in vitro results, five isolates including Ba1, Ba5, Ba8, Ba11, and Ba12 were selected for identification and additional investigations under greenhouse experiments. The selected isolates inhibited the germination of fungal sclerotium and caused mycelial fragmentation and cytoplasmic coagulation. Strains Ba1, Ba5, Ba8, Ba11, and Ba12 belonged to B. mojavensis, Bacillus sp., B. pumilus, Bacillus sp., and B. velezensis, respectively. In the greenhouse trials, the disease severity index was zero in treatments Ba5 (Bacillus sp.) and Ba8 (B. pumilus), similar to Rovral -TS fungicide and completely controlled stem canker disease. Therefore, they are suggested for additional investigations and preparation of optimal formulations.