To fully utilize the characteristic climatic conditions in the southern region of China, a two-crop-a-year cultivation system technique for ‘Kyoho’ grape was developed during the past decade. After summer harvest in June, appropriate pruning and chemical treatments promote flowering and fruiting, which enables a second harvest in late December. Due to climatic differences between the two crop growing seasons, grape phenol and carotenoid metabolism differ greatly. The reported study analyzed the transcriptome of the carotenoid and phenylpropanoid/flavonoid pathways in grapes at four different stages during the two growing seasons. Compared with those in summer grapes, expression levels of the majority of genes involved in the carotenoid metabolic pathway in winter grapes were generally upregulated. This result was associated with lower rainfall and much more abundant sunlight during the second growing season. On the other hand, summer cropping strongly triggered the expression of upstream genes in the phenylpropanoid/flavonoid pathway at E-L 33 and E-L 35. Transcript levels of flavonoid 3’,5’-hydroxylase (F3’5’H), flavonoid 3’-hydroxylase (F3’H), flavonoid 3-hydroxylase (F3H) and glutathione S-transferase (GST) were upregulated in winter grapes at the mature stage. Together, these results might indicate that more flavonoids would be synthesized in ripe winter grapes during the mature stage of the second crop under much drier conditions, longer sunlight hours and lower temperature. These data provide a theoretical foundation for the secondary metabolism of berries grown under two-crop-a-year cultivation systems.

Powdery mildew is an economic threat for viticulture because it not only affects grape yield, but also causes a series of impacts on the qualities of fruit and wine, especially the flavors and various metabolites. Different grape varieties may have different levels of powdery mildew resistance/tolerance and their components of their metabolome are also various. In this study, two wine grape varieties, Guipu No.6 (GP6) and Marselan (Mar) with different levels of powdery mildew tolerance, were used to compare the quality differences in metabolism level by using the widely targeted metabolomics method. The results show that GP6 has a better powdery mildew leaf tolerance than Mar. A total of 774 metabolites were detected by using a UPLC-QQQ-MS-based metabolomics approach, and 57 differential metabolites were identified as key metabolites that were accumulated after infection with powdery mildew in GP6 and Mar, including phenolic acids, flavonoids, terpenoids, stilbenes, lipids, nucleotides and derivatives, lignans and coumarins, and quinones. This finding indicates that the defense mechanisms of grape fruit are mainly associated with phenylpropane-flavonoid metabolism. Specifically, stilbenes had greater variations after powdery mildew infection in GP6; while in Mar, the variations of flavonoids, especially kaempferol-3-O-glucuronide and luteolin-7-O-glucuronide, were more remarkable. The above results demonstrate that stilbenes may play a more important role than flavonoids in resisting powdery mildew infection in GP6’s fruits, and the drastic variations of these phenolic compounds in different wine grapes after powdery mildew infection might also lead to quality difference in the flavors. This study can provide new insights into the understanding of the cause of powdery mildew tolerance in different grape varieties and the effects on the quality of wine grapes infected with the disease exerted by metabolism level.

Vitis adenoclada Hand.-Mazz is a special wild grape resource that is often confused with Vitis heyneana Roem. & Schult in research or production practice, and there are few comprehensive studies on this species in recent years. “Gui Heizhenzhu No. 3” (GH3), as a new germplasm of V. adenoclada found in Guangxi, China, has many advantages, such as good quality and strong adaptability. In this paper, an attempt was made to introduce the breeding process of GH3, including a brief description of its botanical characteristics and its cultivation and management techniques in karst rocky desertification mountains. Meanwhile, its quality-related parameters were evaluated by widely targeted metabolomic analysis. This study indicated that GH3 had the typical botanical characteristics of V. adenoclada, but with larger fruit and a higher sugar content compared to wild or other V. adenoclada grape varieties. Metabolomic study of the target variety showed that glucose and citric acid were the main sugar and acid components in fully ripened berries. Moreover, cyanidin-3-O-glucoside presented as the characteristic anthocyanin. In addition, B-ring dihydroxylation was more active than trihydroxylation in the GH3 berry. Several of its botanical and quality characteristics highlight the unique genetic background of this variety. Thus, it has an important guiding significance and a scientific theoretical basis for identifying, exploiting, and utilizing East Asian wild grape resources.

The anthocyanin profiles and COELAB color values of nine wines in Vitis germplasms from southern China were compared. The results showed that the anthocyanin composition of wines from one hybrid between V. vinifera and V. labrusca ('Moldova'), two V. labrusca varieties ('Conquistador' and 'Saint-Croix'), one V. quinquangularis variety ('Yeniang No.2'), one hybrid between V. quinquangularis and V. vinifera ('NW196'), one V. davidii variety ('Xiangniang No.1') and one V. rotundifolia variety ('Noble') were dominated by anthocyanidin 3,5-O-diglucosides. All these were quite different from V. vinifera wines ('Cabernet Sauvignon' and 'Marselan'), which were characterized by the monoglucoside and pyranoanthocyanins. 3' ,4' ,5'-substituted anthocyanins were dominant in the wines of all varieties, except 'Noble' wine. 'Yeniang No.2' (V. quinquangularis) had the highest acid, total anthocyanin concentration, and showed a more intense pigmentation with a higher proportion and concentration of coumaroylated anthocyanins. On the colorimetric analysis, 'Yeniang No.2' (V. quinquangularis) wine showed the most saturated red colors, followed by 'NW196' (V. quinquangularis). The detected chromatic characteristics of these wines were basically in accordance with their sensory evaluation.Keywords: anthocyanin; wine; HPLC-MS; V. germplasm; variety.Practical Application: Perfecting evaluation system of the anthocyanin characteristics of nine wines in different V. germplasm from southern China.

The establishment and application of a two-crop-a-year cultivation system depends on the particularity of climatic conditions in subtropical regions. The different temperature, light, and water conditions throughout the growing season of summer and winter grapes are the fundamental reasons for differences in primary and secondary metabolites. We performed ultra-high-performance liquid chromatography–triple quadrupole mass spectrometry (UPLC-QQQ-MS)-based metabolomics on ‘Kyoho’ grapes under a two-crop-a-year cultivation system. In total, 1062 metabolites were identified and classified into 10 different categories, while flavonoids were the largest group, with 285 metabolites. Moreover, 876 metabolites were different among the four developmental stages, and 551 were different between the summer and winter grapes during the same growth period. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) clearly distinguished developmental and growth-season differences based on the detected metabolites. Of note, flavonoids were the most important compounds responsible for the differences in berry composition during the growth and developmental seasons. The content of most flavonoids was higher in the winter grapes, but some were also found at higher levels in summer grapes, such as kaempferol-4′-O-glucoside, leucocyanidin, and cyanidin-3-O-glucosylglucoside. Additionally, myricetin-3-O-arabinoside was consistently higher in winter grapes than in summer grapes during all four developmental stages. The extreme high temperature and higher relative humidity were important reasons for the lower flavonoid content in the summer grapes than in the winter grapes. Moreover, the stronger light intensity in the early development of the winter grapes had a positive effect on the accumulation of flavonoids, especially flavonols and flavan-3-ols. This study provides new insights into the metabolism of flavonoids in grapes under a two-crop-a-year cultivation system and explores the climatic causes of the differences in the metabolites in the two crops of grapes.