Effect of some mineral elements on biocontrol efficiency of Bacillus pumilus INR7 against bean damping-off caused by Rhizoctonia solani

Culture design for mass production of biocontrol agents is one of the main approaches in commercialization of biocontrol agents. In this work, effects of some micro-nutrients have been investigated on biomass production and efficacy of B. pumilus against R. solani, the causal agent of bean damping-off. Seven elements, Fe, Zn, Cu, Mo, Mn, Co and B have been used in three concentrations. Bacterial biomass increased significantly in medium ammended with maximum concentrations of Fe (36 and 72 µM) and Cu (7 and 14 µM) and minimum concentration of Mn (12.5 µM). Bacterial population decreased significantly in minimum and medium concentrations of Zn (35 and 70 µM) and maximum concentration of Cobalt (14 µM) compared to M1 basal medium. In greenhouse experiment, highest disease suppression achieved in medium concentration of Fe (36 µM) and maximum concentration of Cu (14 µM). In other hand, maximum concentration of Fe (72 µM), minimum concentration of Zn (35 µM), maximum concentration of Mn (50 µM) and medium concentration of Mo (8.1 µM) decreased efficiency of bacteria in suppression of bean damping-off, significantly. In conclusion, the optimum concentration was not the same for tested elements. Even in the case of individual element, there was difference between optimum concentration for biomass production and efficacy of bacteria in biological control of the plant disease.