Melatonin in Preharvest and Postharvest Management of Fruits and Vegetables: A Critical Narrative Review of Efficacy, Mechanisms, Contradictions and Translational Readiness

Abstract

Fruits and vegetables are highly perishable, and a substantial share of their value is lost between harvest and retail through chilling injury, pathogen decay, enzymatic browning, softening and senescence. Melatonin (N-acetyl-5-methoxytryptamine), an indoleamine produced endogenously by plants, has been proposed as a low-toxicity, naturally occurring treatment that could improve crop performance before harvest and preserve quality afterwards. This critical narrative review evaluates whether the available evidence supports that proposition and under which conditions. Peer-reviewed literature published between January 2014 and 27 July 2026 was identified through multidisciplinary and life-science databases, supplemented by citation tracking, and appraised for design, dose rationale, replication, genotype coverage, storage realism and mechanistic inference. The synthesis indicates that postharvest melatonin treatments most consistently reduce chilling injury, weight loss and oxidative membrane damage, and frequently delay senescence in leafy and floral vegetables. Effects on ripening are direction-dependent: melatonin accelerates ripening in some species and experiments but delays it in others, and responses vary with dose, application route, developmental stage and cultivar. Disease suppression generally reflects induced host resistance rather than direct antifungal activity, and one pathosystem showed increased susceptibility. Preharvest foliar programmes in stone fruits, pomegranate, strawberry, tomato and kiwifruit have improved yield components, harvest quality and storage performance, although field evidence is concentrated in a few research groups, regions and seasons. Mechanistic claims rest largely on correlative enzyme and transcript data, while receptor-level signalling remains contested. Meta-analytic evidence confirms average benefits but reveals high heterogeneity. Economic feasibility, residue behaviour, consumer exposure, formulation stability, regulatory status and life-cycle sustainability remain insufficiently studied. Melatonin can therefore be regarded as a promising but conditionally effective tool whose sustainability credentials are asserted more often than demonstrated. Priorities include dose–response and multi-season commercial trials, genetic and receptor-resolved mechanistic studies, standardised quantification of endogenous melatonin, residue and exposure assessment, and techno-economic and environmental evaluation.