Phytomelatonin in Ornamental Horticulture: A Comprehensive Review of Growth Promotion, Stress Tolerance, and Post-Harvest Quality

The ornamental plant industry faces escalating threats from erratic climate patterns and post-harvest perishability. Phytomelatonin (N-acetyl-5-methoxytryptamine) has emerged as a potent biostimulant capable of addressing these critical bottlenecks. This review synthesizes current knowledge on melatonin's multifaceted roles in ornamental horticulture, clarifying the molecular pathways where it acts as both a direct Reactive Oxygen Species (ROS) scavenger and a signaling molecule orchestrating crosstalk with auxins, abscisic acid, and ethylene. We highlight applications in propagation, where melatonin synergizes with auxins to enhance rhizogenesis and promotes seed germination via hormopriming. Furthermore, we examine melatonin-mediated tolerance to abiotic stresses including drought, salinity, and temperature extremes emphasizing its role in preserving photosynthetic machinery and ion homeostasis. Crucially, the review addresses the post-harvest sector, demonstrating how melatonin extends vase life by repressing senescence-associated genes (SAGs) and antagonizing ethylene biosynthesis. Finally, we discuss future perspectives on genetic bio-fortification and commercial formulations, positioning phytomelatonin as a sustainable tool for securing the resilience and quality of ornamental crops.