Effect of vertical and horizontal canopy on the secondary metabolites in ‘Moldova' grape

Abstract: 【Objective】Since the 21 st century, the climate warming has become more and more obvious.Extreme weather such as high temperature and strong light frequently causes damage to grape. Much attention has been paid upon the effects of high temperature and strong light on the growth of grape leaves and fruit, but little is paid on the effect on the secondary metabolites in grape berries. However, the secondary metabolites in grapes determine the sensory quality and resistance of the fruit, and the phenolic substances including flavonoids and flavanols also play a decisive role in the antioxidant capacity and quality of grape and wine. Flavanols have strong antioxidant capacity, which can effectively remove free radicals in the body, reduce the rough taste of wine, and smooth wine body. They also play a decisive role in the flavor, astringency and stability of grape wine. Anthocyanins directly determine the color and color stability of wine. Previous studies have shown that application of suitable canopy type achieves optimal levels of important secondary metabolites such as anthocyanins. Study of Spayd showed that the surface temperature of the fruit exposed to sunray could be 13 ℃ higher than that of the shaded berries. Chen Jianhong proved that the pergola had a high light energy utilization efficiency, photosynthetic rate of plants, and thus berry productivity. Compared with other cultivation techniques, changing the structure of foliage to regulate the microclimate of grape berries and improve the secondary metabolic quality of the fruit, and is the most simple and feasible technical measure. The purpose of this study is to investigate the differences in the micro-environment and the secondary metabolites in the berries of‘Moldova'between vertical canopy and horizontal canopies.【Methods】Horizontal canopy and vertical canopy were used as the treatments in this sutdy. The temperature and humidity around the grape were collected for two consecutive years from 2015 to 2016. The contents of secondary metabolites in grape berries at different developmental stages were determined from veraison to full maturation, and the growth of new shoots was measured in 2016.【Results】The results showed that compared with the vertical canopy, horizontal canopy significantly decreased the ratio of high temperature and reduced the range of variations in humidity and temperature around the cluster, especially during the hottest months of July and August, when the high temperature generally appeared from 9:00 to 18:00.In 2015, the content of secondary metabolites in berries from horizontal canopy was higher than from the vertical canopy. When the berries became fully mature, the contents of total phenol, flavonoids and anthocyanins in grape berries from horizontal canopy were 5.56%, 44.91% and 27.03% higher than from vertical canopy, respectively. The aroma compound content was also 16.01% higher, but the aroma varieties 16.22% fewer. Measurement of vegetative growth showed that the average length of internode was 4.30% smaller than and branch weight per square meter in the horizontal canopy was only33.33% that of the vertical canopy. The summer temperature in 2016 was cooler than in 2015, and the difference in the contents of secondary metabolites between the two canopy types was less significant.At full maturity, the contents of total phenols, flavonoids and anthocyanins were not significantly different between canopy types; the content of flavanols was significantly (13.67%) higher in the horizontal canopy, but the varieties of fruit flavanols were fewer compared to the vertical canopy. However, the contents of secondary metabolites in both canopy types were higher in 2016 than in 2015.【Conclusion】In years with higher temperatures, horizontal canopy improves the micro-environment for berry development and increases the contents of secondary metabolites in grape fruit compared with the vertical canopy.