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.

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.

Flavonoids play an important role in forming wine grapes and wine quality characteristics. The flavonoids of three winter red wine grapes, Yeniang No. 2 (YN2), Marselan (Mar), and Guipu No. 6 (GP6), were analyzed by ultra-high-performance liquid chromatography–triple quadrupole mass spectrometry (UPLC-QQQ-MS). Furthermore, the flavonoids in GP6 grapevines using two types of training systems, namely, trellis (T) and espaliers (E), were also compared in this study. Overall, 196 flavonoid metabolites, including 96 flavones, 38 flavonols, 19 flavanones, 18 polyphenols, 15 anthocyanins, 7 isoflavones, and 3 proanthocyanidins, were identified. The flavonoid profiles were remarkably different among these three grape varieties, while they did not change much in the GP6 managed on trellis and espaliers. Grape varieties with different genetic backgrounds have their own unique flavonoid profiles. Compared with Mar-T, isoflavones and flavonols presented higher contents in GP6-T and YN2-T, which mainly contain glycitein, genistin, calycosin, kaempferide, isotrifoliin, and ayanin. The anthocyanin content was significantly higher in YN2-T than in the other two varieties. YN2 and GP6-T present a more stable color, with significantly more acetylated diglucosides and methylated anthocyanins in YN2-T and GP6-T than in Mar-T. Notably, GP6 had more varied flavonoids and the better characteristics to its flavonoid profile out of these three varieties, due to it containing a higher number of anthocyanins, flavone, and flavonols and the greatest number of different flavonoid metabolites (DFMs), with higher contents than YN2 and Mar. Compared with the trellis training system, the espaliers training system increased the content of flavonoids detected in GP6 grape berries; however, the composition of flavonoids strictly depends on the grape variety.

Background: The global transcriptome reprogramming in grapevines in response to powdery mildew remains poorly understood, despite its economic implications, especially the new cultivars. Methods: Thus, this study aimed to elucidate these changes through RNA sequencing in ‘Yeniang No. 2’ grapevine leaves infected with powdery mildew compared to healthy ones. Results: A total of six samples were subjected to transcriptome sequencing, resulting in 36.85 Gb of clean data. A minimum of 5.89 Gb of clean data was generated for each sample, with at least 92.24% of the clean data attaining a quality score of Q30. Clean reads from each sample were aligned to the designated reference genome. The mapping ratio varied between 88.77% and 89.66%. The high-quality sequencing data revealed 1219 differentially expressed genes (DEGs), of which the infection upregulated 790 and downregulated 429. Functional enrichment analyses revealed a significant activation of key defense-related pathways. These included plant–pathogen interaction, phenylpropanoid and flavonoid biosynthesis for creating antimicrobial compounds, glutathione metabolism for reducing oxidative stress, and oxidative phosphorylation for enhanced energy production. This indicates a coordinated, multi-faceted defense strategy. The study also uncovered a complex layer of post-transcriptional regulation, identifying 1883 novel genes and 22,210 alternative splicing events, primarily skipped exons and intron retention. Key hub proteins identified within interaction networks, along with these splicing changes, underscore a sophisticated defense involving transcriptional reprogramming and metabolic shifts. Conclusions: The genes and molecular markers discovered are valuable resources for marker-assisted breeding. Leveraging these findings, particularly hub genes and favorable splice variants, can accelerate the development of new grapevine cultivars with durable resistance to powdery mildew.

Grapevine is one of the most extensively cultivated and economically important fruit crops, renowned for its nutritional and health benefits. However, salt stress severely impairs its growth, development, and yield. Rootstocks play a crucial role in enhancing salt stress tolerance in grafted grapevines, however the underlying mechanisms particularly at morphophysiological and transcriptomic study remain poorly understood and require further investigation. Therefore, in the present study, morphophysiological and transcriptomic sequencing was performed on tolerant grapevine rootstock ‘SO4’ and susceptible ‘Beida’ in response to salt stress and control group. Morphophysiological results showed that the plant height, stem diameter, root length, root weight, number of roots, root surface area, malondialdehyde, soluble sugar, proline, antioxidants enzymes after 12 days of salt stress boosted more significantly in ‘SO4’ than ‘Beida’. Furthermore, transcriptomic analysis studies showed that a total of 2268, 1066, and 1135 differentially expressed genes (DEGs) were identified in ‘SO4’, and ‘Beida’ rootstock after 0, 6, and 12 days. The metabolic pathways, pyruvate metabolism, plant hormone signal transduction, biosynthesis of secondary metabolites, and osmotic adjustment were the primary response systems in both grapevine rootstock under salt stress. Different transcription factors involving bHLH, AP2, ERF, HSF, WRKY, MYB, and MYB-related had more annotated in ‘SO4’ than ‘Beida’ rootstock under salt stress. In addition, using weighted gene coexpression analysis (WGCNA), five modules (MEblack, MEblue, MEyellow, MEgreen, and MEgrey) were highly associated with salinity stress tolerance. Among them, MEblack was the most positive (upregulated) module color in ‘SO4’, while it was negatively correlated with ‘Beida’ rootstocks under salt stress. Furthermore, 10 DEGs related to the tolerance response were selected and validated based on transcriptomic data and RT-qPCR. Our findings outline a tolerance mechanism model for rootstocks under abiotic stress, providing necessary information for improving the tolerance of grapevine genotypes.