Bioformulations of Novel Indigenous Rhizobacterial Strains for Managing Soilborne Pathogens

Abstract

The antagonistic potential of indigenous strains of Bacillus, Paenibacillus, and Pseudomonas isolated from potato rhizosphere or soil and soybean plants to manage soil and root diseases of vegetable crops is presented here as a case study. These bacterial strains were also characterised for production or activities of antibiotics, metabolites, volatiles, phytohormones, and lytic enzymes. In agar plate assays, most of the strains showed broad-spectrum antagonistic activity against various selected fungal and oomycete pathogens. Irradiated peat was found to be a suitable carrier material for preparing formulations of these bacteria and delivering them on seed, root, or substrate. In pot experiments, irradiated peat formulations of these bacteria provided control of Pythium damping-off and root rot and Phytophthora blight and root rot of cucumber, Rhizoctonia damping-off of radish, and Fusarium crown and root rot and Fusarium wilt of tomato. Bacterial treatments also resulted in higher fresh weights of plants produced in pathogen-infested substrate. In micro-plot trials, coating of seed potato tubers with irradiated peat formulation of some of these antagonistic bacteria reduced scab severity on daughter tubers and increased tuber weights when treated tubers were planted in a potato soil with a history of common scab disease. These disease suppression and plant-growth promotion activities of various bacterial strains might be related to the production of different antibiotics, secondary metabolites, lytic enzymes, phytohormones, siderophores, and volatiles. The results of these studies indicate that several of the bacterial strains isolated from local sources showed their potential use as biofungicides for protection of seedling damping-off and root rot and tuber diseases caused by various soilborne pathogens.