Effects of pre-harvest melatonin treatment on storage quality and texture of two sweet cherry cultivars

【Objective】Sweet cherry (Prunus avium L.) is highly valued for its bright coloration, crisp texture and pleasant sweetness; however, its high metabolic activity and fragile skin make the fruit extremely vulnerable to postharvest deterioration, particularly under cold storage, where weight loss, textural decline and color fading frequently occur. In recent years, melatonin (MT) has been reported to participate in plant stress mitigation and postharvest physiological regulation, yet the effects of preharvest application on cold-stored sweet cherries remain insufficiently defined, especially regarding cultivar-dependent responses. Therefore, this study aimed to evaluate the influence of different MT concentrations applied at various developmental stages on fruit physicochemical quality during refrigerated storage, and to provide theoretical guidance for the precise application of melatonin in sweet cherry production.【Methods】Two commercial sweet cherry cultivars, Luying 3 and Luying 5, grown under identical orchard conditions, were subjected to foliar sprays of exogenous MT at the hard-core stage （25 days after full bloom, DAFB）, the color-break stage (45 DAFB), and three days before harvest (55 DAFB). Multiple MT concentrations were compared. After harvest, the fruits were stored at 4 ℃ under controlled relative humidity. At 0, 7 and 14 days of storage, weight loss, total soluble solids (TSS) content, texture profile analysis (TPA) parameters (including hardness, springiness, cohesiveness, gumminess and chewiness), and color metrics (L*, a*, b*) were evaluated according to standard postharvest testing protocols. Multivariate analyses, including principal component analysis (PCA) and a correlation heatmap, were used to elucidate relationships among measured variables and to comprehensively discriminate the storage performance of different treatments. Statistical differences were tested at P≤0.05.【Results】The application of MT demonstrated clear concentration- and cultivar-dependent effects. During cold storage, weight loss increased significantly with storage time in both sweet cherry cultivars, with consistently higher values observed in Luying 5 than in Luying 3. High melatonin concentrations (0.30 mmol·L-1 ) significantly exacerbated weight loss at the late storage stage in both cultivars, whereas low to moderate concentrations partially alleviated weight loss at specific storage periods. Total soluble solids (TSS) content generally declined during storage; however, melatonin treatments differed in their ability to maintain TSS levels, with lower concentrations showing a relatively positive effect and higher concentrations accelerating TSS content depletion. In both cultivars, low-concentration MT (0.05-0.10 mmol· L- 1 ) consistently preserved higher TSS content, implying a delayed reduction in fruit sweetness during cold storage. MT treatment also mitigated the decline of TPA hardness and maintained superior textural integrity, possibly by stabilizing cell wall structure or suppressing pectin solubilization. Colorimetric analyses revealed that MT inhibited undesirable increases in a* values and modulated shifts in L* and b*, implying delayed pigment oxidation and improved external appearance. Notably, fruit redness in MT-treated groups developed more uniformly, and surface brightness remained relatively stable. The correlation heatmap indicated that hardness, TSS content and chromatic parameters were positively associated and were critical determinants of fruit sensory acceptability. PCA analysis further demonstrated that these indicators accounted for the majority of variance among treatments, effectively distinguishing MT-treated fruits from the control at later storage stages. Cultivar-dependent responses were evident: Luying 5 exhibited high sensitivity to MT, particularly in adhesion- related texture attributes and mass retention, whereas Luying 3 displayed comparatively milder responsiveness across most parameters. At 14 days of storage, fruits treated with lower MT concentrations generally maintained higher overall quality scores, whereas excessive concentrations induced variable and sometimes negative results. These findings highlight the importance of dosage optimization in preharvest regulation.【Conclusion】Preharvest foliar application of melatonin at appropriate concentrations can effectively delay postharvest quality deterioration in sweet cherry fruits during cold storage. MT contributes to the maintenance of fruit weight, the conservation of soluble solid levels, the retention of desirable texture properties and the stabilization of color attributes. However, responses differ considerably among cultivars, underscoring the necessity of tailoring treatment strategies to specific genotypic characteristics. Low MT concentrations (0.05-0.10 mmol · L- 1 ) are generally recommended for enhancing sweetness, firmness and surface brightness, while excessive concentrations may induce adverse effects, particularly in cultivars with lower tolerance.