Melatonin is a crucial regulator of fruit growth and development. However, the mechanisms by which pre-harvest application of melatonin regulates the metabolism of phenolic compounds in pear pericarp remain poorly understood. In this study, the effect of pre-harvest spraying of melatonin on the synthesis of phenolics in pear peel and the regulatory mechanism were investigated using a multi-disciplinary approach, integrating physiological and biochemical, transcriptomic, and metabolic analyses, and the “Yuluxiang” pear as the test material. The pre-harvest spraying of 100 μM melatonin notably increased the single fruit weight, total soluble solids (TSS) and total soluble solids/titratable acid (TSS/TA) ratio. In addition, the spraying regimen elevated the concentrations of phenolic substances, including anthocyanosides, chlorogenic acid, and lignin, in the fruit peel. Three comparison groups (T0 vs. CK0, T1 vs. CK1, and T2 vs. CK2) showed 354, 1385, and 816 differentially expressed genes (DEGs) and 240, 411, and 210 differentially expressed metabolites (DEMs), respectively. Transcriptome results from melatonin treatment significantly affected the key metabolic pathways, including signal transduction, hormone regulation, glucose metabolism, secondary metabolites biosynthesis, phenylpropanoid biosynthesis, and flavonoid biosynthesis. Melatonin treatment also influenced the expression of key genes in phenylpropanoid biosynthesis and flavonoid biosynthesis pathways, such as PAL, C4H, 4CL, CAD, CHS, UFGT, POD, and others. Metabolomic data suggested the melatonin treatment notably stimulated the biosynthesis of l-phenylalanine, cinnamic acid, caffeic acid, ferulic acid, leucocyanidin and uridine 5ʹ-diphospho-d-glucose than control. By examining the expression patterns of transcription factors, we identified 12 transcription factors (TFs), including PbrMYB4, PbrMYB36-like, PbrMYB14, PbrREF4 and PbrNAC6-like, as potential key TFs involved in melatonin-regulated polyphenol biosynthesis. The pre-harvest application of 100 μM melatonin can help improve the visual and flavor quality of pear fruits. It can influence the key enzyme genes’ expression of phenolic metabolism while stimulating the production of l-phenylalanine, cinnamic acid, caffeic acid, ferulic acid, leucocyanidin and uridine 5ʹ-diphospho-d-glucose, which promote the biosynthesis of anthocyanidins, phenolic acids, and lignins. These findings provide comprehensive insights into the metabolic mechanisms of melatonin-regulated phenolic compounds in pear peels.

Nutrient patterns can significantly influence the growth and development of fruit trees, especially fruit quality. In order to clarify the appropriate ratio of inorganic and organic fertilizers, six treatments with different ratios of cow manure and chemical fertilizers were set up in this study to evaluate the effects of different treatments on fruit yield, appearance quality, intrinsic quality and volatile substances. The results showed that, after replacing some chemical fertilizers with cow manure, the content of sugar, titratable acid, organic acid and aroma substance in the fruit increased, the fruit yield and colour did not change significantly, and the fruit weight per fruit decreased. Among the treatments of cow manure with chemical fertilizer, the fruits of 50% chemical fertilizer with 50% cow manure treatment had higher titratable acid (0.4%), malic acid (4.15 mg/g), sorbitol (0.51%), glucose (1.30%), fructose (5.81%) content and total aroma substance content (1047.82 μg/g) than chemical fertilizer alone. Compared to the fertilizer treatment alone, the application of cow manure instead of 50% of the chemical fertilizer had a positive effect on fruit quality.

Dwarfing rootstocks are regularly used to cultivate apples in apple‐producing countries, including China. Here, we investigated how the use of different dwarfing interstocks affects the growth vigour, morphology, and physical and biochemical indices of Huahong apple saplings. This information was used to elucidate possible mechanisms involved in dwarfing. We found that the degree to which trees were dwarfed differed (63%–83%) with different dwarfing interstocks. Preliminary correlation analysis and factor analysis showed that internode length and the number of root tips represented the main morphological indices for evaluating the dwarfing effects of dwarfing interstocks. In addition, shoot water potential, net photosynthetic rate, indole‐3‐acetic acid oxidase activity and starch content could be used as physiological and biochemical indices for evaluating the degree of dwarfing. These data provide important insights about the dwarfing mechanisms of dwarfing interstocks to help improve the cultivation methods used for apple production.

Melatonin is an important regulator of fruit growth and development. To explore the physiological mechanism whereby preharvest melatonin application regulates the polyphenol content of ‘Yuluxiang’ pear peel, we sprayed 0.1 mM melatonin during the first fruit expansion and early color change periods, and the control group were sprinkled with fresh water. Then, we measured the contents of anthocyanin, lignin, and major monomeric phenolics and the activities of key enzymes associated with phenolic metabolism. The results showed that melatonin application significantly increased the content of total phenolics, total flavonoids, total anthocyanins, and lignin in the peel from the color change to mature development stages. Near maturity, the activities of all key enzymes, except dihydroflavonol-4-reductase, were higher than those in the control samples, but significant differences in enzyme activity occurred at different time points. Compared with the control group, the fruit peels of the melatonin-treated plants exhibited a higher antioxidant activity and accumulated more flavonols. Thus, preharvest spraying of melatonin can alter the activity of key enzymes associated with phenolic metabolism, increasing the total phenol, flavonoid, anthocyanin, and lignin contents, which in turn, affects the color, strength, and antioxidant capacity of pear peels.