Tomato mosaic virus (ToMV) is one of the economically damageable Tobamovirus infecting the tomato in Egypt that has caused significant losses. It is therefore of great interest to trigger systemic resistance to ToMV. In this endeavor, we aimed to explore the capacity of ZnO-NPs (zinc oxide nanoparticles) to trigger tomato plant resistance against ToMV. Effects of ZnO-NPs on tomato (Solanum lycopersicum L.) growth indices and antioxidant defense system activity under ToMV stress were investigated. Noticeably that treatment with ZnO-NPs showed remarkably increased growth indices, photosynthetic attributes, and enzymatic and non-enzymatic antioxidants compared to the challenge control. Interestingly, oxidative damage caused by ToMV was reduced by reducing malondialdehyde, H₂O₂, and O₂ levels. Overall, ZnO-NPs offer a safe and economic antiviral agent against ToMV.

Viruses pose a serious threat to the sustainable production of economically important crops around the world. In the past 20 years, potato virus Y (PVY) emerged as a relatively new and very serious problem in potatoes, even though it is the oldest known plant virus. Multiple strains of the virus cause various symptoms on the leaves and tubers of potatoes, resulting in yield reduction and poor-quality tubers. Consequently, it would be very interesting to learn what causes systemic PVY resistance in plants. Natural compounds such as chitosan (CHT) and phosphorus have been developed as alternatives to chemical pesticides to manage crop diseases in recent years. In the current study, potato leaves were foliar-sprayed with chitosan and phosphorus to assess their ability to induce PVY resistance. Compared to untreated plants, the findings demonstrated a significant decrease in disease severity and PVY accumulation in plants for which CHT and P were applied. Every treatment includes significantly increased growth parameters, chlorophyll content, photosynthetic characteristics, osmoprotectants (glycine betaine, proline, and soluble sugar), non-enzymatic antioxidants (glutathione, phenols, and ascorbic acid), enzymatic antioxidants (peroxidase, superoxide dismutase, lipoxygenase, glutathione reductase, catalase, β-1,3 glucanase, and ascorbate peroxidase), phytohormones (gibberellic acid, indole acetic acid, jasmonic acid, and salicylic acid), and mineral content (phosphorus, nitrogen, and potassium), compared to infected plants. However, compared to PVY infection values, CHT and P treatments showed a significant decrease in malondialdehyde, DPPH, H₂O₂, O₂, OH, and abscisic acid levels. In addition, increased expression levels of some regulatory defense genes, including superoxide dismutase (SOD), ascorbic acid peroxidase (APX), relative pathogenesis-related 1 basic (PR-1b), and relative phenylalanine ammonia-lyase (PAL), were found in all treated plants, compared to PVY-infected plants. Conclusion: Phosphorus is the most effective treatment for alleviating virus infections.

Phytopathogenic fungi pose a critical threat to global food security through substantial pre- and post-harvest crop losses, intensified by climate change and fungicide resistance. To address this, we synthesized low-concentration chitosan–inorganic oxide nanocomposites (CS-SiO₂, CS-ZnO, CS-CuO) via ionic gelation, a green and scalable method. Comprehensive characterization (DLS, UV-Vis, FTIR, XRD, SEM) confirmed nanocomposite formation, CS-SiO₂ exhibited uniform particle sizes (200–250 nm), while CS-CuO showed slightly larger particles, all with excellent dispersity. Zeta potential analysis confirmed strong colloidal stability, with pure chitosan nanoparticles (CSNPs) displaying a surface charge of +12.9 mV, while all nanocomposites retained positive charges, enhancing adhesion to negatively charged fungal membranes. In vitro antifungal assays against Alternaria alternata, Botrytis cinerea, Colletotrichum graminicola, and Fusarium graminearum demonstrated hierarchical efficacy: CS-CuO > CS-ZnO > CS-SiO₂, with CS-CuO achieving >80% growth inhibition against B. cinerea and A. alternata. SEM revealed severe hyphal damage and spore collapse in CS-CuO-treated fungi, attributed to synergistic reactive oxygen species (ROS) generation and chitosan-mediated membrane disruption. In vivo trials on B. cinerea-infected apples showed CS-CuO reduced lesion area by 81% and elevated host defense markers, including a 1.5-fold increase in total phenolic content and higher DPPH radical scavenging activity compared to controls. These nanocomposites, particularly CS-CuO, offer a sustainable, dual-action solution direct antifungal activity and enhanced host resilience while minimizing environmental impact. By integrating scalable synthesis, eco-compatibility, and efficacy, this work advances chitosan–inorganic oxide nanocomposites as viable alternatives to conventional fungicides, with immediate potential for agricultural and postharvest applications.