Biostimulants and fruit crop performance: Mechanistic insights and agronomic outcomes

• Mechanistic pathways of biostimulants in fruit crops are critically synthesized. • Hormonal, metabolic, plant–microbe, and redox processes underpin biostimulant action. • Crop-specific and environment-dependent responses explain field-level variability. • Environmental, regulatory, and economic constraints limiting adoption are identified. • Emerging opportunities, including nano-biostimulants, are discussed for fruit systems. The growing demand for sustainable horticultural production under increasing environmental and climate-related constraints has intensified interest in alternatives to conventional agrochemicals. Plant biostimulants have emerged as effective tools for improving fruit crop performance by modulating plant physiological and metabolic processes rather than supplying nutrients or acting as pesticides. This review critically synthesizes progress in biostimulant research published between 2010 and 2024, with a specific focus on fruit crops. The principal mechanisms of biostimulant activity are systematically explored, including improvements in nutrient acquisition and utilization efficiency, hormone-like modulation of growth, stimulation of beneficial soil microbial populations, activation of plant defense responses, regulation of primary and secondary metabolic pathways, and alleviation of oxidative stress. Major classes of biostimulants—such as seaweed extracts, humic and fulvic substances, protein hydrolysates, beneficial microorganisms, and emerging nano-biostimulants—are evaluated with respect to their impacts on yield, fruit quality parameters, and tolerance to abiotic stresses. Evidence drawn from apple, citrus, grape, cherry, strawberry, pomegranate, and other fruit crops underscores both the considerable agronomic potential of biostimulants and the variability in crop responses, which is largely influenced by formulation type, application strategy, and environmental conditions. The review also highlights key challenges, including inconsistent field-level performance, limited mechanistic understanding, the absence of standardized evaluation protocols, and fragmented regulatory frameworks. Finally, future research directions are proposed, emphasizing the need for long-term field experimentation, integration of omics-based methodologies, and regulatory harmonization to facilitate the effective and responsible deployment of biostimulants in sustainable and climate-resilient fruit production systems.