Indian Journal of Microbiology

A recently published method allowed counting of both total number of microorganisms and those antagonistic to a disease causing fungus in naturally occurring materials such as composts. Using this method and Fusarium solani, cause of black root rot of chickpea, as the target fungus, five of the nine materials [termitaria soil, compost from leaf-liter and kitchen waste, debris in the leaf-axil of plants of Billbergia sp. and six composts used by organic farmers and called as biodynamic (BD) preparations – BD500, BD502, BD503, BD504, BD505, BD506] were found to have high population (4.28 log₁₀ to 6.98 log₁₀ g⁻¹ material) of antagonistic bacteria. Fifty five (82%) of the 67 isolates were Gram-positive spore-forming rods and the rest non-sporulating. All the 55 spore-forming antagonistic bacteria survived for at least 108 days in a desiccator; 20 survived for at least 17 months. Antagonistic bacteria surviving desiccation for long periods can potentially be used in dry formulations as biocontrol agents. Presence of large number of antagonistic spore forming bacteria in these different materials appears to be responsible for the reported low pest incidence at the farms using BD preparations. Thirty-five of the 67 isolates showed commensal behaviour towards groundnut rhizobia, under in-vitro conditions. Eleven of the 55 spore-forming bacteria were studied using Biolog kit. Only one, BCB 103, was identified as Bacillus thermoglucosidasius, others did not match any of the 23 spore-forming species (including B. thuringiensis) in its database.