Sodium Alginate–Gelatin Coated Nanodelivery System with pH-Responsiveness Enhances Rice Resistance to <i>Magnaporthe oryzae</i> by Potentiating Immune Responses

Magnaporthe oryzae causes a fungal disease that poses a serious risk to global food security. Nanoagrochemicals are perceived as sustainable, economical, and environmentally friendly alternatives to traditional pesticides. Plant immune activators can be applied as the active ingredients of nanopesticides to control diseases in agriculture, but their use is limited and corresponding research is lacking. In this study, a nanodelivery system (PBZ@CaCO3@SG) for the on-demand release of a plant immune activator (probenazole; PBZ) was prepared using nano-CaCO3 after coating with sodium alginate–gelatin (SG). In vitro, at 48 h, the release rate reached 97.9% and 88.4% at pH 4.5 and 6.0, respectively, which greatly exceeded that under neutral conditions (pH 7.4), with acid-responsive release characteristics. Moreover, it responded quickly to the acidic microenvironment generated during M. oryzae infestation and rationally released PBZ, effectively improving plant resistance to M. oryzae and minimizing disease. Notably, M. oryzae infection was markedly reduced, by 60.6%, after PBZ@CaCO3@SG treatment. Mechanistically, PBZ@CaCO3@SG enhanced both physical barrier formation and systemic acquired resistance in rice, enhancing resistance to M. oryzae. It also showed good biosafety for both microbial communities and earthworms in the soil. This comprehensive study revealed multiple mechanisms by which PBZ@CaCO3@SG interacts with plants and pathogens, inhibits damage, and maintains nontarget biosafety, emphasizing its great potential for plant disease management.