Effect of simple rain-shelter cultivation on flavonoid profiling in Vitis vinifera ‘Cabernet Sauvignon' grape berries

Abstract: 【Objective】Different from the white wine grape berries, the red wine grape berries contain flavonoid metabolites such as anthocyanins, flavon-3-ols and flavanols. Flavonoids are important components that determine the color, taste and aging potential of the wine, and their composition and content in the fruits directly affect the quality of the wine. Although the effects of rain-shelter cultivation on the accumulation of phenolic compounds in grape berries have been described considerably, the results are not consistent due to variations in climates and culture variables. The influence of rain-shelter cultivation on flavonoid profile in developing grape berries has not yet been investigated in detail. The present study assessed the variations in the composition and contents of various flavonoid components during the development of grape berries (Vitis vinifera‘Cabernet Sauvignon') under the rain-shelter and openfield cultivations in two cropping seasons, and analyzed the impact of the rain-shelter cultivation on flavonoid metabolism in grape berry. The outcome of the study would provide guidance to viticulturists and winemakers who consider the application of rain shelter in wine grape production.【Methods】The experiment was carried out in 2012 and 2013 in the vineyard of Changyu Aibifu International Winery in Miyun County, Beijing. The test materials used in this experiment were self-rooted seedlings of V. vinifera‘Cabernet Sauvignon'colonized in 2003. In the experiment, three experimental plots with similargrowth status of grapevine plants were selected. Three experimental plots (regarded as three biological replicates) were set up in each of the two cultivation methods. There were 40 grapevines in each plot.The simple rain shelter was built with a height of 185 cm (about 12 cm from the top of the canopy) , a width of 110 cm and a roof curvature of 125 cm. The covered material was 6.5 filament longevity film, which was polyethylene anti-aging film with a thickness of 0.10-0.12 mm and light transmittance about 80%. Sampling interval was 1-2 weeks until the berries were fully ripe. In rainy days, the sampling time was 1-2 days in advance or postponed. According to this principle, grape berries were sampled at 20, 37, 50, 64, 71, 78, 87, 97, 112, 125 and 135 DAF for the 2012 vintage and at 14, 28, 41, 57, 67, 78, 97, 112 and 124 DAF for the 2013 vintage, of which the first two sampling dates had samples only under openfield cultivation. Samples were analyzed for weight, volume, Brix, p H and total acids. The flavonoid components, including flavonols, flavan-3-ols and anthocyanins were qualitatively analyzed during the development of the berries under the rain-shelter cultivation and the open-field cultivation by high performance liquid chromatography-mass spectrometry (HPLC-MS) .【Results】During the two years, the weight of grape berry showed a typical double“S”pattern during the growth process. As the fruit developed, the weight gradually increased. And there was no significant difference in ripening and harvest period. The trend of fruit volume was similar to that of fruit weight in the two years, but in 2012 the berry volume under open-field cultivation was always higher than that under rain-shelter cultivation. The trend of sugar/acid ratio was the same under the two cultivation modes in the two years. In both years, the weight and the volume of the berries during harvest period were higher in 2013 than in 2012. The sugar/acid ratio was higher in 2012 under the two cultivation types. The HPLC-MS results showed that the composition of flavonols, flavan-3-ols and anthocyanins were not modified under rain-shelter cultivation in comparison to that under the open-field cultivation. Generally, the rain-shelter cultivation led to increased concentrations of flavonols, in particular the accumulation of 3'4'-substituted quercetins, and it also elevated the proportion of 5'-methylated flavonols and 5'-methylated flavan-3-ols. However, the total content of flavan-3-ols was hardly affected under rain-shelter cultivation. Besides, this cultivation mode promoted the synthesis of 3'4'5-substituted dephinidin-form anthocyanins in the two experimental years as well, although it was observed that the rain-shelter measurement produced different impacts on anthocyanin production. The total content of anthocyanins in rain-sheltered fruit in 2012 was significantly higher than in fruit produced under open-field cultivation, but the opposite situation appeared in2013. This was possibly because the more rainfall in 2012 enlarged the difference between the two cultivation modes. Partial least square discriminant analysis (PLS-DA) indicated that anthocyanins changed most significantly among the three kinds of flavonoids in the berries, and dephinidin-3-O-glucoside-6-coumaroyl was obviously reduced in the rain-sheltered grapes in both years, whereas petunidin-3-O-glucoside-6-coumaroyl was markedly raised.【Conclusion】The rain-shelter cultivation could minimize the variation in the synthesis of flavonoids especially anthocyanins in berry skin caused by climate changes.