Microbial biocontrol in agriculture: from mechanistic Understanding to field application

Abstract Modern agriculture faces significant challenges in crop protection, with plant diseases causing substantial global losses and conventional chemical pesticides posing risks to human health, the environment, and fostering pathogen resistance. This review offers a comprehensive overview of biological control agents (BCAs) as a sustainable and environmentally friendly alternative for managing plant diseases. It elucidates both their direct and indirect mechanisms of action. Direct biocontrol mechanisms, including antibiosis (production of antimicrobial metabolites), mycoparasitism, competition for nutrients and space, and the secretion of lytic enzymes, directly inhibit or kill pathogens and pests. Indirect mechanisms focus on enhancing host plant resilience and modifying the surrounding ecosystem; these encompass the induction of systemic resistance (ISR/SAR) in plants, promotion of plant growth and nutrient acquisition, positive ecosystem modification (e.g., improved soil fertility and stress tolerance), and the attraction of natural enemies of pests. The review further explores the genetic underpinnings of these diverse mechanisms, emphasizing how advancements in genomics and genetic engineering are revolutionizing BCA development, enabling a shift from empirical selection to rational design for enhanced efficacy and specificity. Finally, it discusses the multi-tiered validation process for biocontrol strategies, from initial in vitro screenings to controlled greenhouse studies and crucial real-world field trials, highlighting the need for rigorous testing to confirm practical applicability. Collectively, BCAs emerge not merely as biopesticides but as multifunctional biostimulants and biofertilizers, integral to developing robust, resilient, and sustainable agricultural systems.