Biopolymer-engineered novel chitosan-copper-β-glucan nanocomposite: A sustainable antifungal innovation for enhanced plant immunity and crop yield.

The development of resistance in phytopathogenic fungi to conventional fungicides, coupled with escalating environmental and health concerns, necessitates the development of eco-compatible next-generation antifungal agents. This study presents the development and evaluation of novel biopolymer-based metallic-chitosan‑copper-β-glucan (CN-Cu-BG) tri-element nanocomposite (NC) synthesized via microwave-assisted methods. Detailed nanomaterial characterizations confirm the formation of uniformly spherical NCs (~41.97 nm) with integrated copper signatures indicative of successful composite formation. These embedded copper nanoparticles (Cu-NPs) within a dual biopolymer matrix have enhanced antifungal efficacy, plant immune response and yield-promoting effects. In-vitro antifungal assays against Sclerotium rolfsii (causal agent of sugarbeet root rot) and Cercospora longipes (causal agent of sugarcane brown spot) revealed complete mycelial growth inhibition at a concentration as low as 200 ppm of the CN-Cu-BG NC. Foliar application of CN-Cu-BG NC at 50 ppm in sugarbeet increased chitinase and β-glucanase activities by 673% and 681%, respectively and boosted chlorophyll content by 72%. Beet weight improved by 80%, with a 74% disease control. Multivariate analyses identified PPO, β-glucanase, chitinase and chlorophyll as key markers associated with enhanced disease control (r = 0.84-0.94). Heatmap, PCA and PLS-DA confirmed the superior performance of CN-Cu-BG NC at 50 ppm across biochemical, physiological and yield parameters. These findings demonstrate CN-Cu-BG NC as a scalable, eco-compatible nanobiopolymer offering a potent alternative to chemical fungicides, integrating nanobiotechnology with sustainable crop protection and circular bioeconomy practices.