Citrus Flavonoids-Coated Biogenic Nanoparticles for Controlling Xanthomonas axonopodis pv. citri: Antimicrobial Efficacy and NMR-Based Investigation of Bacterial Metabolic Reprogramming.

Citrus canker, caused by the Gram-negative bacterium Xanthomonas axonopodis pv. citri poses a major threat to global citrus production, with increasing resistance to copper-based pesticides and antibiotics. This study presents a sustainable approach for bacterial control using biogenic silver nanoparticles (AgNPs) synthesized via green methods and functionalized with citrus peel-derived flavonoids, hesperidin and hesperetin. These flavonoid-coated nanoparticles─AgNP@HSD and AgNP@HST, respectively─were structurally characterized, confirming successful biofunctionalization and providing insight into flavonoid-nanoparticle interactions. Antimicrobial assays demonstrated potent inhibitory effects against X. axonopodis pv. citri, with both formulations outperforming streptomycin in terms of minimum inhibitory concentrations. Mechanistic investigations revealed distinct antimicrobial pathways: AgNP@HSD induced a broad stress response marked by elevated amino acid levels and extensive membrane damage, while maintaining intracellular ATP and NAD(P)H levels, suggesting a metabolic adaptation strategy. In contrast, AgNP@HST triggered targeted oxidative stress, leading to significant depletion of energy and redox metabolites, indicating collapse of cellular homeostasis. This differential behavior is attributed to the higher intrinsic bioactivity of hesperetin, the aglycone form of hesperidin. Our findings underscore the potential of citrus flavonoid-coated biogenic nanoparticles as eco-friendly biomaterials for plant disease management. The integration of green nanotechnology with plant-derived metabolites offers a promising alternative to conventional agrochemicals for the control of citrus canker and other phytopathogenic threats.