Harnessing acquired immunity in plants towards sustainable crop protection

Acquired immunity in plants, including systemic acquired resistance (SAR) and induced systemic resistance (ISR), plays a central role in protecting crops against a wide spectrum of pathogens and pests, ranging from fungi and bacteria to viruses and nematodes. Over the last three decades, significant advances have been made in understanding the molecular basis of SAR and ISR, particularly the roles of salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) pathways, their crosstalk, and the transcriptional reprogramming mediated by key regulators such as NPR1, WRKY, and TGA transcription factors. This review summarizes current knowledge on how biological elicitors (e.g., plant growth-promoting rhizobacteria, endophytes, and fungi), chemical inducers (e.g., SA/JA analogues, chitosan, phosphites, peptides), and emerging nanomaterials (e.g., graphene oxide and metal nanoparticles) activate plant immune responses through both direct antagonism and priming of defense pathways. Special emphasis is placed on recent insights into hormonal interactions, redox regulation, and systemic signaling that shape long-lasting immunity. Furthermore, the practical implications of elicitor-based approaches are discussed in the context of Integrated Disease Management (IDM), highlighting both commercially available products and novel research directions. By integrating mechanistic insights with translational applications, this review establishes a comprehensive framework for leveraging acquired immunity to reduce dependence on synthetic pesticides and strengthen sustainable crop resilience under changing climatic conditions.