Plant Nano‐Immunoengineering and Biostimulant Applications of Ti₃C₂T<i>_x</i> MXene Colloids for Enhanced Systemic Defense against Phytopathogens and Stress Resistance Mechanisms

Abstract The large‐scale implementation of antimicrobial agrochemicals to increase plant resistance against invasive phytopathogenic organisms and to secure crop yields and quality imposes critical cost and environmental challenges in agriculture. Thus, there is a growing need for alternative sustainable methods in today's farming to boost the plants’ growth and immune systems, safeguarding them from biotic stresses more eco‐economically. In this context, interest in the potential applications of functional carbon‐based nanomaterials has surged due to their tunable physicochemical/biological properties. MXenes, the latest materials in this family, are revolutionizing various fields in biology‐medicine, as they have been shown to possess intrinsic anti‐inflammatory/antimicrobial/anticancer properties and biocompatibility with different cells/tissues at controlled doses, opening avenues for advancing nanoagriculture. Here, innovative applications of mixed‐low‐dimensional titanium carbide MXene (Ti 3 C 2 T x )‐based aqueous colloids are reported for plant immunoengineering and biostimulation, including autoclave‐treated Ti 3 C 2 T x nanosheets’ impacts on enhancing defense‐related biological responses, seed‐to‐seedling transition, and underlying gene/hormone regulatory mechanisms. Foliar application of their relatively low doses serves as elicitor/priming active and stomatal closure‐inducing agent to boost plant innate immunity, expression of defense genes, systemic disease resistance, and defense/growth‐related responses. This sophisticated bioactivity resulted in reactive‐oxygen‐species production, inducing anti‐phytoviral/anti‐phytobacterial/anti‐phytofungal modes‐of‐action through direct pathogens‐inhibition and indirect regulation of plant immune system, implying MXene's potential for agricultural‐protection‐by‐nanodesign.