Effects of kaolin particle film coatings on the water-saving efficiency and fruit quality of Cabernet Sauvignon (Vitis vinifera L.) grape plants in the Ningxia region of China

Water is the main limiting factor for plant growth, especially in arid areas where viticulture requires extremely high amounts of water. The leaves of 'Cabernet Sauvignon' (Vitis vinifera L.) in Yinchuan, Ningxia, China, were sprayed with kaolin particle film (KPF) before the color change of grapes in 2020 and 2021. The study aimed to determine 'Cabernet Sauvignon' grapes photosynthetic index, water use efficiency, and the ripening fruit's primary physicochemical index and phenolic content. KPF had no significant effect on overall plant growth indicators and yield of Cabernet Sauvignon grapes. In contrast, reduced their net photosynthetic rate (27.45-40.57%), stomatal conductance (34.23-72.5%) and transpiration rate (30.94-72.34%) under deficit irrigation; thereby improving water use efficiency (18.45-64.40%). KPF increased reducing sugars (4.19-11.74%) and soluble solids (2-16.09%) in 'Cabernet Sauvignon' grapes while reducing the 100-berries weight and titratable acid of the grape. Moreover, it increased the anthocyanin content (4.71-29.23%) of 'Cabernet Sauvignon' grape skins and decreased the total phenolic content. KPF spraying significantly decreased in total flavonoids, flavanols and total phenols under deficit irrigation, however, no significant effect was observed on tannins in the seeds. Spraying KPF increased the overall content of monomeric anthocyanins compared to the no-sprayed controls. These results suggest that KPF can improve the water use efficiency of Cabernet Sauvignon grape plants and alter the total flavonoid content (TFo), total anthocyanin content (TAC), total flavanol content (TFa)and total phenolic content (TPC) of the grapes. Thus, KPF has the potential to be applied as an anti-transpirant agent to improve water conservation and fruit quality in arid and semi-arid regions.