Natural products for biocontrol of Pseudomonas syringae: mechanisms and applications

<i>Pseudomonas syringae</i> functions as a model phytopathogen causing numerous crop diseases, resulting in substantial economic losses in global agriculture. Presently, management of <i>P. syringae</i> predominantly depends on chemical pesticides; however, their prolonged application has contributed to escalating resistance and environmental contamination, highlighting urgent requirement for sustainable biological control approaches. In this review, we examine recent advances in the utilization and mechanistic understanding of natural products derived from plants, animals, and microorganisms for the control of <i>P. syringae.</i> Plant-derived compounds-including flavonoids, terpenoids, and alkaloids-inhibit <i>P. syringae</i> infection by targeting the bacterial type III secretion system (T3SS), disrupting cell membrane integrity, promoting reactive oxygen species (ROS) accumulation, and activating plant immune signaling pathways such as salicylic acid (SA) and jasmonic acid (JA) cascades. Animal-derived substances, such as chitosan, propolis, and antimicrobial peptides, primarily exert antibacterial effects through membrane disruption and immune system stimulation. Microbial-derived natural products contribute to synergistic disease suppression by modulating host immunity and interfering with the pathogen's quorum sensing mechanisms. Evidence indicates that these natural products possess multi-target antimicrobial properties, offering a rich repository of candidate molecules, such as baicalein, lignans, and carvacrol, for the development of eco-friendly antibacterial agents. Future investigations should focus on detailed characterization of these bioactive compounds and their specific disease targets, optimization of extraction methodologies to improve stability and bioavailability, and comprehensive assessment of environmental safety to advance the industrial implementation of sustainable biocontrol strategies.