Synthesis, characterization, and antifungal activity of chitosan–copper nanocomposites against crop pathogens

Chitosan-copper nanoparticles (CHT-Cu NPs) were synthesized using an ionic gelation approach and evaluated for their physicochemical properties and antifungal activity against major fungal pathogens of chickpea and citrus. For instance, "In recent years, nanotechnology-based formulations have emerged as promising strategy for sustainable disease management". Dynamic light scattering analysis revealed uniformly sized nanoparticles (~150 nm) with low polydispersity and a positive surface charge (+22.2 mV). Fourier transform infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive X-ray analysis confirmed effective copper coordination, amorphous nanocomposite formation, and stable incorporation of copper within the chitosan matrix. The antifungal efficacy of CHT-Cu NPs was assessed <i>in vitro</i> against <i>Colletotrichum ciceri</i>, <i>Fusarium ciceri</i>, <i>Rhizoctonia bataticola</i>, <i>Sclerotium rolfsii</i>, and <i>Colletotrichum gloeosporioides</i>. The nanocomposites exhibited strong, concentration-dependent inhibition of mycelial growth. <i>F. ciceri</i> was highly sensitive, showing complete inhibition at all tested concentrations (≥100 µg mL^-¹). <i>S. rolfsii</i> and chickpea pathogens <i>C. ciceri</i> and <i>R. bataticola</i> were completely inhibited at concentrations 200 µg mL^-¹, 300 µg mL^-¹ and 300 µg mL^-¹, respectively, whereas <i>C. gloeosporioides</i> was comparatively less sensitive and required higher concentrations (≥400 µg mL^-¹) for complete suppression. In contrast, chitosan alone and copper sulfate showed only moderate antifungal activity. These findings demonstrate that CHT-Cu NPs possess broad-spectrum antifungal activity and superior efficacy compared to conventional fungicides, highlighting their potential as eco-compatible nanobiopesticides for sustainable management of fungal diseases in crop plants.