Antifungal effectiveness of histidine loaded chitosan nanoparticles against papaya root rot caused by Fusarium solani and physiological responses on papaya.

Management approaches for fungal diseases in Papaya primarily depend on inorganic chemical-based fungicides, which may pose threats to both human health and the environment. Nano based-fungicides offer innovative solutions with significant potential to transform the plant protection sector and enhance overall quality of life. This study examined the antifungal efficacy of histidine loaded chitosan nanoparticles (His-CS NPs) against Fusarium solani through both in vitro and pot experiments. Additionally, the His-CS NPs were characterized using sophisticated techniques. Dynamic light scattering methods indicated that the NPs had a uniform size of 314.4 nm, a low polydispersity index (PDI) of 0.218, viscosity (1.43 Cps), higher zeta potential (11.2 mV), nanoparticle concentration/mL (3.53 × 10), conductivity (0.046 mS/cm), encapsulation efficiency (53 %), loading capacity (24 %) and yield (32.17 %). In vitro assays revealed mycelial growth inhibition of 74.27 ± 2.3 % (p < 0.05) at 0.03 % His-CS NPs. Pot experiments showed significant reduction in disease severity to 6.3 ± 1.5 % compared to 62.0 ± 3.4 % in the untreated control (p < 0.001). His-CS NP treatment also improved plant height (22.3 ± 0.8 cm), leaf area (154.8 ± 4.5 cm), and stem diameter (10.5 ± 0.3 mm), along with increased antioxidant enzyme activity (SOD, POD, CAT, PPO), reduced ROS levels (HO, O), and elevated chlorophyll content (3.78 ± 0.11 mg/g FW, p < 0.01). The interaction of chitosan (CS) with His-CS nanoparticles (NPs) was demonstrated through fourier-transform infrared (FTIR) spectroscopy; concurrently, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) highlighted the porous nature of the structure. The evaluation of the disease through in vitro and pot experiments revealed that His-CS NPs exhibited significant antifungal activity, effectively inhibiting mycelia growth, diminishing disease severity, and attaining a greater percentage efficacy of disease control (PEDC). Application of His-CS NPs to Papaya potted plants via seed treatment and foliar spray positively affected growth parameters, the activity of antioxidant-defense enzymes, levels of reactive oxygen species (ROS), and chlorophyll content. Hence, the antifungal properties of His-CS NPs open new avenues for creating biologically derived antifungal prototype, providing a sustainable and renewable alternative to conventional botanical based strategies.