Fate of formulated and non-formulated Trichoderma strains after application in the soil and side effects on non-target microorganisms

Trichoderma spp. are saprophytic fungi that have gained increasing attention as biocontrol agents against soilborne plant pathogens. However, the decline of the population of Trichoderma spp. in the soil often renders field treatments inefficient. This decline depends on the applied strain of Trichoderma spp., the soil abiotic factors, namely temperature, moisture and pH, and the complex interactions with the microbial biomass of a soil and the plants. Since increasing the initial inoculum concentration of Trichoderma spp. does not prevent the decline of the population, formulations were often proposed to overcome this obstacle. Formulations can enhance the proliferation of the fungus and increase consistency of soil treatments, but can be ineffective when the plant pathogen is present at high levels in the soil. In addition, they must avoid any excess of nutrients that can advantage soilborne plant pathogens. Understanding the behaviour of Trichoderma spp. and soil microbiota after the inoculation is crucial to enhance the efficiency of the treatments. Applications of Trichoderma spp. can shift the microbial community of the soil, but with a transient effect. Although culture-independent analysis partially clarified the impact of introducing Trichoderma spp. on soil microbiota, several aspects of the complex interactions among the plants and soil microorganisms, including plant pathogens, over time are still unknown. Moreover, the effect of agricultural practices on the survival of introduced isolates of Trichoderma spp. needs to be explored to improve biocontrol in practice