Bioscience Evidence 2026, Vol.16, No.4, 221-234 http://bioscipublisher.com/index.php/be 224 Anthocyanin accumulation in peach peel is highly dependent on light, and shading greatly reduces fruit coloration. Sunlight induces the expression of PpHYH, which, together with PpBBX4, activates the PpMYB10 gene cluster and promotes anthocyanin accumulation in the sun-exposed peel. Under dark conditions, PpCOP1 accumulates in the nucleus and suppresses this process (Zhao et al., 2022). Both UVA and UVB promote fruit coloration in 'Hujingmilu', and the combined treatment has a stronger effect than either alone. PpHY5 acts as a key regulator in this UV signaling pathway by upregulating anthocyanin biosynthesis genes such as PpCHS, PpDFR, and PpMYB10.1 (Zhao et al., 2021). Different cultivars respond differently to light quality. For example, 'Yulu' shows little response to UVA but responds well to UVB, indicating that the effect of light management on fruit coloration is genotype-dependent (Zhao et al., 2017). Blue light induces anthocyanin accumulation more effectively than red or green light, partly because it increases both PpHYH transcription and the proportion of its highly active splice variant PpHYH-X2 (Zhao et al., 2023) (Figure 1). Laying reflective film on the orchard floor seven days before harvest significantly improved peel coloration in 'Taiko' peach and increased the expression of anthocyanin biosynthesis genes such as F3H and CHS, although it had no significant effect on soluble solids, acidity, or firmness (Lee et al., 2021). Bagging greatly reduces light exposure to the fruit surface. In a Florida study, peaches harvested without bagging contained about twice as much anthocyanin as fruits kept in white bags and about six times more than fruits in colored liner bags, while most internal quality traits were not significantly affected by bag color (Campbell et al., 2021). Peel color is also an important indicator of fruit maturity. The Color Development Index (CDI) is closely related to the Index of Absorbance Difference (IAD) and reaches a plateau around the climacteric stage. Therefore, standardized color monitoring can help determine harvest timing, although measurements should avoid direct sunlight to reduce errors (Scalisi et al., 2022). Figure 1 Effects of visible light with different wavelengths on anthocyanin accumulation in peach peel. (a) The peel coloration of 'Jinxiu' treated with red, green and blue light or under dark conditions. (b) Anthocyanin accumulation of peach peel treated with red, green and blue light or under dark conditions. Error bars in (b) show the standard error (SE) of three biological replicates (Adopted from Zhao et al., 2023) 3.2 Source-sink balance and sugar accumulation Flower and fruit thinning improves the leaf-to-fruit ratio and reduces competition among fruits for photoassimilates, allowing the remaining fruits to receive more carbon throughout development. As a result, fruits achieve greater growth potential and better harvest quality. Excessive crop load reduces fruit quality, while fruits supplied with sufficient carbon show better appearance and internal quality even at the same maturity stage. In 'Cresthaven' peach, different thinning intensities caused clear metabolic differences during the early growth stage. At harvest, fruits grown under adequate carbon supply had higher dry matter and soluble solids, indicating that high-quality fruit is not produced simply by sugar accumulation during the final stage but is strongly influenced by early metabolic priming (Anthony et al., 2020). Sugar accumulation is also regulated by canopy position and light conditions through their effects on the source-sink relationship. Fruit quality development involves carbohydrate metabolism, changes in sugar and
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