Application of Plant Defence Elicitors in Fruit Crop Protection with a One Health Approach

Plant defence elicitors have emerged as pivotal components of sustainable fruit crop protection, aligning with One Health principles by reducing chemical residues while enhancing ecosystem and human health. These exogenous agents—ranging from phytohormones, peptides, and cell-wall fragments to botanical extracts—activate or prime innate immune responses in fruit crops through pattern-triggered immunity (PTI), systemic acquired resistance (SAR), and induced systemic resistance (ISR) pathways. Over the last decade, advances in receptor biochemistry, genomics, metabolomics, and epigenetics have transformed this field. Recent mechanistic advances reveal that oligosaccharide elicitors derived from chitosan and laminarin are perceived by membrane-localised pattern recognition receptors (PRRs) that confer broad-spectrum resistance against fungal, bacterial, and viral pathogens in fruits. By contrast, no specific protein receptor has been identified for harpin proteins, the emerging evidence indicating that harpin perception may occur through direct interaction with plasma-membrane lipids or lipid-associated proteins. The One Health approach is supported by elicitors, biodegradability, minimal environmental persistence, and the ability to reduce synthetic fungicide usage by 30–70%. However, challenges remain regarding batch-to-batch variability, sensory acceptance due to bitter compounds, regulatory hurdles for novel food approvals, and the need for optimised application protocols that consider the fruit genotype and developmental stage. The future integration of nanotechnology for targeted delivery, the artificial-intelligence-driven screening of active molecules, and synergistic combinations with biocontrol agents promises to overcome these limitations, positioning plant defence elicitors as cornerstone tools for resilient, health-promoting fruit production systems.