Improving the efficacy of biocontrol agents against soilborne pathogens

Technical, economical and environmental factors are forcing to adopt new sustainable methods, such as the use of microbial antagonists, for the control of soilborne pathogens. Research has mainly focused on antagonistic fungi and bacteria, often not providing consistent or satisfying results. Biocontrol agents can be combined with other chemical products, with physical methods (solarization or steam sterilization) or agronomical practices, such as enhancement of suppressive soils, use of amendments or microbial optimization in the case of soilless systems. Different biocontrol strategies should be developed for different pathogens. The use of microorganisms can play an important role in a more complex vision of crop protection, as a key element of IPM programs. Mixtures of antagonists with complementary activities could be developed, but the need for multiple registration is critical. Genetic manipulation could result in new biocontrol strains with increased production of toxic compounds or lytic enzymes, improved space or nutrient competence, wider host range or enhanced tolerance to abiotic stresses. The potential risks related to the environmental release of genetically modified microorganisms must be carefully assessed. Genes and enzymes involved in the biocontrol mechanism could be applied directly or transferred to crops. Finally, the production system, formulation and methods of application (soil and seed treatment or microbial colonization of the hydroponic nutrient solution) are crucial to maintain and improve the efficacy of microbial antagonists.