Direct Antifungal Effects of Actinobacteria as Biocontrol Agents Against Pre- and Postharvest Diseases in Fruits, Vegetables, and Cereals

Pre- and postharvest losses caused by fungal infections represent one of the greatest constraints in agricultural production worldwide. Due to increasingly stringent regulations, as well as environmental and health concerns associated with their use, synthetic fungicides have been restricted, driving the development and application of sustainable alternatives within the framework of integrated plant disease management. Among these, Actinobacteria (also referred to as Actinomycetota) have attracted considerable attention over the past decades due to their versatile metabolites and plant growth-promoting properties, supporting their potential application as bacterial biocontrol agents. Their activity against phytopathogenic fungi is largely associated with direct antagonistic mechanisms. Currently, special attention is paid to the excreted secondary metabolites, lytic enzymes, volatile organic compounds and their in vitro antifungal activity. Therefore, this review summarizes current knowledge on these direct mechanisms, aiming to support the future application of actinobacteria and their metabolites as part of biological plant disease management strategies.