Influence of electrical conductivity on biological activity of Pythium ultimum and Binab T in a closed soilless system

The effects of electrical conductivity (EC) of the nutrient solution on the performance of the commercial biocontrol product Binab T against the root pathogen Pythium ultimum were studied in order to identify supporting factors to increase the efficiency and decrease the inconsistency of biocontrol agents in closed cultivation systems. Using a substrate-based growing system, the commercial product Binab T with the active strains Trichoderma polysporum plus T. harzianum was evaluated at four different EC levels (1.5, 2.5, 3.5 and 5.0 mS cm(-1)) over seven weeks in a controlled climate chamber environment, using tomato as the model plant. Addition of the biocontrol agent to the cultivation system caused a reduction in the level and incidence of pathogen attack that improved with increasing EC level from 2.5 mS cm(-1) onward. Production of the cell wall-degrading enzymes cellulose and glucanase by Binab T increased with increasing EC level, independent of pathogen presence. In a control treatment with no artificial inoculation, enzyme activity decreased with increasing EC level. Increasing EC levels in the presence of Binab T also had a positive effect on plant biomass. The highest antagonistic effect of Binab T against Pythium ultimum, as indicated by enzyme activity, amount of pathogen in the system and disease incidence, occurred at 3.5 mS cm(-1). The plant growth-promoting effect of Binab T also peaked at 3.5 mS cm(-1).