International Journal of Horticulture, 2025, Vol.15, No.6, 290-298 http://hortherbpublisher.com/index.php/ijh 295 and content of phenols is inconsistent, with anthocyanin increases reported in a few studies, and there being no consistent differences in others. The effectiveness of leaf removal is determined by the timing, the variety, and local weather, but the contribution of climate is usually less than the contribution of genes. European, North American, and South American case studies cite the success of this method in disease control and quality assurance but with yield loss as a common compromise (VanderWeide et al., 2021). 6.2 Practical experience and limitations in domestic studies In past decades, studies in China and other domestic regions have shown that leaf removal at the fruit-zone can improve anthocyanin and flavonols contents in grape cultivars such as Cabernet Sauvignon and Marselan, while inducing limited effects on soluble solids content and berry weight (Lu et al., 2021; Li et al., 2023; Yao et al., 2024). In Jieshishan in eastern China, where there is rainy summer weather, leaf removal was found to lower titratable acidity of grapes but had no big effect on soluble solids content (Yao et al., 2024). At the same time, this treatment consistently enhanced anthocyanin and flavonol accumulation in berries and, consequently, grape color potential. However, in Cabernet Sauvignon, early defoliation negatively affected the synthesis of carotenoid-derived compounds (e.g., β-damascenone), showing varietal effects. The findings also underscore the importance of adapting defoliation operations to local conditions, since too much sun exposure and heat could lead to sun scald of berries or loss of desirable volatile compounds. The constraints are fluctuating effects based on vintage and cultivar and the need for further optimization of defoliation timing and severity in different grape varieties and climatic conditions (Figure 3). Figure 3 Meteorological conditions and grape physicochemical parameters; daily maximum, average, and minimum temperatures (lines) and precipitation (histograms) recorded from 1 July to 1 October at the Chateau Langes weather station in 2021 (A) and 2022 (B). Time axis of Cabernet Sauvignonand marselan berry development and ripening in 2021 (C) and 2022 (D). (Adopted from Yao et al., 2024) 6.3 Varietal and regional differences in outcomes Varietal and regional difference is also crucial in the decision of leaf removal effects. For example, in Italy and China, studies confirmed that anthocyanin and flavonol accumulation response to leaf removal is highly genotype-dependent, with some increase in flavonols in cultivars and no change in anthocyanins. In semi-arid conditions like those of Xinjiang, distal (upper canopy) leaf removal is used to retard ripening and mitigate global warming, resulting in increased flavonol content and improved aroma but sometimes at the expense of postponed
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