In China’s drought-prone grape-growing regions, high summer temperatures and scarce precipitation often lead to prolonged water deficits, exposing grapevines to heat stress. This results in accelerated fruit ripening, elevated sugar content, reduced acidity, and compromised wine flavor and quality. Under such water-scarce conditions, balancing irrigation water conservation with raw material quality improvement has become a critical challenge.

This study investigated the combined effects of regulated deficit irrigation (RDI) and anti-transpirant (AT) application on fundamental quality indicators of Cabernet Sauvignon grape berries and wine quality. The objective was to identify an optimal combination strategy that simultaneously could achieve water conservation and enhance wine quality.

The experiment was conducted at Longyu Winery in Xixia District, Yinchuan City, Ningxia in 2024, using Cabernet Sauvignon grapes as materials. From early July (berry swelling stage), regulated deficit irrigation treatments (RDI-1: 40% ETc (evapotranspiration), RDI-2: 60% ETc, and RDI-3: 80% ETc) were implemented, and ATs were sprayed twice in August. Starting from late July, grapes were harvested every two weeks to measure basic physicochemical indicators. On September 12, the grapes were harvested and used to produce Cabernet Sauvignon dry red wine. After fermentation, the physicochemical indicators and various phenolic compound indicators of the wine were measured.

The synergistic application of regulated deficit irrigation (RDI) and ATs significantly enhanced soluble solids and total acid content in grapes while markedly suppressing reducing sugar accumulation, which contributed to reduced alcohol content in wine. The RDI-2-AT group exhibited the lowest alcohol content (11.94% vol). The RDI-1 group showed the lowest total organic acid content (5.01 g·L^-1), whereas the RDI-2-AT group demonstrated a 12.40% increase in tartaric acid content compared with the RDI-2 group. Total phenolics exhibited a gradient increase with intensified water deficit, but anti-transpirant-treated groups showed significant reductions (14.83%, 21.33%, 22.59%, and 32.45% lower than that under CK group). Specifically, the RDI-1-AT group had 26.89% lower phenolic acid monomers than the RDI-1 group. The RDI-3 group recorded the highest total monomeric phenolics (163.74 mg·L^-1), 3.54% higher than that under CK group, while the RDI-2-AT group had the lowest value (115.4 mg·L^-1), significantly below the CK group. For monomeric anthocyanins, the CK group had the lowest total value (23.38 mg·L^-1), whereas the RDI-1 group had the highest value (34.82 mg·L^-1). Both RDI-1-AT and RDI-3-AT groups showed significantly lower monomeric anthocyanin contents than their non-anti-transpirant counterparts (RDI-1 and RDI-3 groups).

The combined application of 60% ETc regulated deficit irrigation (RDI-2) and ATs (RDI-2-AT) could increase total acid and phenolic content in wine while reducing volatile acidity and alcohol content. This synergistic approach thereby enhanced the taste profile and stability, demonstrating the most significant improvement in wine quality.