PRB4 and infection: In addition, CS-NPs have been loaded with active ingredients, including Harpin protein [56], Cu [46], Zn [39], SA [24], and thiamine [57], that can induce plants’ defense systems against infections of R. solani (tomato), C. lunata (maize), F. verticillioides (maize), and F. oxysporum (chickpea) by inducing CAT, chitinase, PAL, PO, POD, PPO, protease, SOD, β-1,3-glucanase activity, O2-, H2O2 content, and lignin localization.