Evaluation of Formulation-Dependent Antimicrobial Activity and Plant Compatibility of Chitosan-Based Silver Nanoparticles

Chitosan-based silver nanoparticles (Ch-AgNPs) are emerging as promising antimicrobial materials with potential applications in crop protection. This study evaluated the formulation-dependent antimicrobial activity and plant compatibility of Ch-AgNPs synthesized from chitosan extracted via different routes from shrimp shells. Antibacterial activity was assessed against representative Gram-negative and Gram-positive model bacteria (Escherichia coli and Staphylococcus aureus), as well as phytopathogenic bacteria (Xanthomonas campestris, Pseudomonas syringae), using disk diffusion assays. Antifungal activity was evaluated against Fusarium graminearum in vitro and in a controlled growth chamber. All formulations exhibited concentration-dependent antibacterial activity, with L10 and L20 formulations derived from optimized lactic acid-based extraction routes and DP4 derived from an inorganic deproteinization-based extraction route showing the highest efficacy at 1.0 mg/mL. Strong antifungal activity was observed, particularly for L10 and DP4, achieving mycelial growth inhibition of 92% and 84%, respectively, at 1.0 mg/mL. Seed germination and seedling growth assays confirmed that all formulations were non-phytotoxic at 1.0 mg/mL, with L10 and DP4 significantly enhancing germination parameters and early plant growth. Under controlled conditions, these formulations also reduced the incidence and severity of crown and root rot in spring wheat caused by F. graminearum. These findings demonstrate that optimized Ch-AgNP formulations combine antimicrobial activity with plant compatibility, highlighting their potential for crop protection, pending further environmental safety and agronomic validation under field conditions.