To explore the impact of shade treatment on grape berries, ‘Marselan’ grape berries were bagged under different light transmission rates (100% (CK), 75% (A), 50% (B), 25% (C), 0% (D)). It was observed that this treatment delayed the ripening of the grape berries. The individual weight of the grape berries, as well as the content of fructose, glucose, soluble sugars, and organic acids in the berries, was measured at 90, 100, and 125 days after flowering (DAF90, DAF100, DAF125). The results revealed that shading treatment reduced the sugar content in grape berries; the levels of fructose and glucose were higher in the CK treatment compared to the other treatments, and they increased with the duration of the shading treatment. Conversely, the sucrose content exhibited the opposite trend. Additionally, as the weight of the grape berries increased, the content of soluble solids and soluble sugars in the berries also increased, while the titratable acidity decreased. Furthermore, 16 differentially expressed genes (DEGs) were identified in the photosynthesis-antenna protein pathway from the transcriptome sequencing data. Correlation analysis revealed that the expression levels of genes VIT_08s0007g02190 (Lhcb4) and VIT_15s0024g00040 (Lhca3) were positively correlated with sugar content in the berries at DAF100, but negatively correlated at DAF125. qRT-PCR results confirmed the correlation analysis. This indicates that shading grape clusters inhibits the expression of genes in the photosynthesis-antenna protein pathway in the grape berries, leading to a decrease in sugar content. This finding contributes to a deeper understanding of the impact mechanisms of grape cluster shading on berry quality, providing important scientific grounds for improving grape berry quality.

Clonal selection is essential for adapting wine production to specific terroirs. To characterize clonal variation in berry quality, five ‘Merlot’ clones (M343, VCR1, VCR3, VCR13, and VCR101) grown in the Hexi Corridor region of Gansu Province, China, were evaluated during the 2024 growing season. An integrated analysis of morphological, physicochemical, phenolic, metabolomic, and volatile traits was conducted to provide a multidimensional assessment of clone-specific berry quality under the arid conditions of this region. VCR1 exhibited the highest total soluble solids and anthocyanin contents, alongside the largest number of annotated metabolites. VCR101 had the highest titratable acidity and the most diverse flavonoid profile, whereas VCR13 showed the highest total soluble sugar content. VCR3 had the highest tannin and total phenolic contents and also exhibited the greatest number and total semi-quantitative relative abundance of volatile compounds. These findings demonstrate that, under arid conditions, the clones differ in their accumulation patterns of sugars, organic acids, phenolics, and aroma-related metabolites. Exploratory principal component analysis identified VCR3 and VCR1 as promising candidates for production objectives emphasizing different quality attributes. These findings provide practical information for clonal selection, germplasm evaluation, wine grape breeding, and region-specific cultivation under arid environmental conditions.