In the contemporary context, the increasing concerns surrounding fungal infections in crops have spurred collaborative efforts among multidisciplinary researchers. These infections destroy one-third of all food crops annually, resulting in substantial economic losses [1]. One of the underlying causes of this problem is the resistance of many fungal species to several commercially available fungicides [2,3]. Additionally, fungal phytopathogens can produce mycotoxins, contaminating crops, water, and soils and posing potential risks to human health and herbivores [4]. On the other hand, the widespread utilization of chemical fungicides presents an environmental challenge due to the non-eco-friendly nature of many of these compounds [5]. These nonbiodegradable chemicals accumulate in vital resources such as water, soils, and plants [6,7], leading to significant, far-reaching consequences such as the quality of plantations, environmental contamination, and human and animal poisoning. In such circumstances, a reliable solution to this problem lies in developing safe and biocompatible alternative pesticides. These pesticides have no toxicological effects on humans or animals while minimizing environmental pollution and effectively controlling various fungal plant diseases [8].

Due to the unique properties and tremendous applicability of nanomaterials, they have become at the forefront of multiple cutting-edge fields, including industry, biotechnology, and medicine. In recent years, nanomaterials have garnered considerable interest in contemporary agriculture. The development of nanopesticides offers a new perspective for more efficient and nontoxic control of plant diseases while reducing the dependence on potentially harmful chemical pesticides [9]. Chitosan (CS) and its derivatives are among the most promising natural compounds for the development of such nanopesticides owing to their biocompatibility, nontoxicity, and biodegradability. Chitosan is widely utilized in diverse fields, such as medicine, biotechnology, and the food industry [10]. The industrial form of chitosan is derived from the partial deacetylation of chitin. CS is a linear polysaccharide heteropolymer consisting of repeating units of N-acetylglucosamine and glucosamine. CS exhibits solubility only in an acidic aqueous medium with a pH below 6.5 owing to the presence of free NH2 functional groups. Within this pH range, the amino groups become protonated, affording the polymer a crucial polycationic nature. This positive charge enables CS to exhibit high reactivity and engage in electrostatic interactions with counter anions, negatively charged molecules, and surfaces such as cell surfaces [11].

Nanotechnology allows the use of various CS formulations, such as nanofibers, nanocomposites, nanocapsules, and nanoparticles [[12], [13], [14], [15], [16]]. Many studies have demonstrated the marked broad-spectrum antifungal activity of different CS formulations [[17], [18], [19]] against various economically significant fungal species, including Aspergillus niger, Fusarium solani [20], Rhizopus sp., Colletotrichum capsici, C. gloeosporioides, F. graminearum [21], and Botrytis cinerea [22]. The primary proposed mechanism for the antifungal activity of chitosan involves permeabilization of the cell membrane [23]. The antifungal effectiveness of CS is closely tied to its physical-chemical properties, such as its molecular weight, degree of acetylation/deacetylation [24], and charge [20], which enables the production of diverse CS nanomaterials with modulated properties that are effective and selectively inhibit the growth of pathogenic fungi. Moreover, CS has been proven to be safe and nontoxic for plants and even exhibits protective and growth-stimulating effects that could lead to increased crop productivity [25].

Hybrid nanocomposites (NCs), among the latest and most innovative chitosan-based nanomaterials, serve antifungal and agricultural purposes [25]. These NCs are created by incorporating inorganic nanoparticles into the CS polymer matrix, resulting in a nanocomposite that combines the properties of both components [26]. The commonly used inorganic nanoparticles include metals (Ag, Cu, Zn), metal oxides (ZnO, CuO), and semimetals and their oxides (Si and SiO2) [27], which have been proven to be potent antifungal agents. For instance, ZnO and CuO nanoparticles have demonstrated effectiveness against Botrytis cinerea, Penicillium expansum [28], and Fusarium oxysporum [29,30]. Furthermore, recent studies have shown that inorganic silicon-based nanomaterials possess antimicrobial activity and excellent biocompatibility [31,32]. The mechanism underlying the antifungal activity of inorganic nanoparticles, particularly those containing metal oxides, is believed to involve nanotoxicity, encompassing the production of reactive oxygen species and oxidative stress [33]. Therefore, the incorporation of such active inorganic nanoparticles into the CS matrix is believed to synergistically enhance the antifungal activity of chitosan [27].

In our study, we introduce newly synthesized CS-based NCs incorporating several oxides (ZnO, CuO, and SiO2) that possess characteristics that make them promising candidates for effective and safe nanopesticides. We aimed to evaluate their antifungal activity against two highly significant agricultural pathogens: Alternaria solani (A. solani) and Fusarium solani (F. solani). F. solani is a destructive pathogen that causes root decay in economically important plant species, such as peas, soybeans, and common beans [[34], [35], [36]]. Conversely, A. solani causes an infectious disease called early blight on the leaves of tomatoes and potatoes [37,38]. Furthermore, we investigated alterations in fungal membranes and detected different markers of oxidative stress, revealing the molecular mechanism underlying fungal antifungal activity. Our findings hold promise for the future agricultural application of these CS-based NCs as nanopesticides. Moreover, these findings help to elucidate the molecular mechanisms underlying the interactions of CS nanomaterials with pathogenic fungi.