Influence of cluster thinning and girdling on aroma composition in 'Jumeigui' table grape

Comparative Analysis of the Evolution of Green Leaf Volatiles and Aroma in Six Vitis vinifera L. Cultivars during Berry Maturation in the Chinese Loess Plateau Region

Green leaf volatiles (GLVs) are important in giving grape a fresh and green aroma. But the changes in GLVs during the phenological development of grapevines are not well known. This study analyzed the GLVs and transcription levels of associated biosynthetic genes in six grape species from the Loess Plateau region at five stages of maturation. Thirteen GLVs were detected, showing unique patterns for each grape type at various growth phases. The primary components in six grapes were (E)-2-hexenal, (E)-2-hexen-1-ol, and hexanal. With the exception of Cabernet Franc in 2019, the overall GLV contents of the six types generally increased during growth and development, peaking or stabilizing at harvest. And Sauvignon Blanc, Cabernet Gernischt, and Cabernet Sauvignon exhibited higher total contents among the varieties. PLS-DA analysis revealed 3-hexenal's high VIP scores across two years, underscoring its critical role in grape variety classification. Correlation analysis revealed a strong positive correlation between the levels of hexanal, 1-hexanol, (E)-2-hexen-1-ol, (Z)-3-hexenyl acetate, nonanal, and (E, E)-2,6-nonadienal and the expression of VvHPL and VvAAT genes in the LOX-HPL pathway. Specifically, VvHPL emerges as a potential candidate gene responsible for species-specific differences in GLV compounds. Comprehending the changing patterns in the biosynthesis and accumulation of GLVs offers viticulturists and enologists the opportunity to devise targeted strategies for improving the aromatic profile of grapes and wines.

Suitable crop loading: An effective method to improve "Shine Muscat" grape quality

Berry thinning was applied to control crop load of "Shine Muscat" grape variety. Primary and secondary metabolites released during berries development were monitored, and the correlation between physicochemical parameters and core aroma compounds was analyzed. Results revealed a significant increase in single-berry weight and sugar-acid ratio of berries under low crop load conditions. Furthermore, phenolic content and antioxidant activity under low crop load were significantly higher than those of the other groups. Grapes with low crop loads also exhibited better aroma characteristics and higher sensory scores than those of the other groups, chiefly due to significantly increased terpene and C₁₃-norisoprenoid contents and substantially decreased C₆ compound and aldehyde contents. Moreover, correlation analysis revealed total soluble solid accumulation was positively correlated to terpene accumulation, while hexanal, 2-hexanal, (E)-2-hexanal, and (E)-2-octenal were positively correlated with titratable acidity content. Thus, better grape quality could be achieved by precisely controlling berry crop load.

Geographical differentiation of Molixiang table grapes grown in China based on volatile compounds analysis by HS-GC-IMS coupled with PCA and sensory evaluation of the grapes

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Volatile fingerprints of three Molixiang grapes were established using HS-GC-IMS.

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GC-IMS coupled with PCA could distinguished the three Molixiang grapes well.

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Sensory evaluation revealed significant (P ≤ 0.05) difference among the three samples.

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E-2-octenal, styrene and benzaldehyde were potential geographical marker compounds.

In this study, the volatile fingerprints of GC-IMS showed great differences on the volatile profiles of Molixiang grapes collected from three different regions of China, which suggested that aroma of table grapes could be largely impacted by origin areas. Butyl lactate, E-2-octenal and Z-2-pentanol were mainly contained in MLX-A, the grapes sampled from Ningbo, China. High contents of p-cymene, styrene and γ-terpinene were observed in MLX-B grapes sampled from Beizhen, China. In addition, benzaldehyde and methyl benzoate were major contained in MLX-C grapes sampled from Zhangzhou, China. The PCA results revealed effective differentiation of samples from different geographical origin based on the information obtained from GC-IMS. Furthermore, sensory evaluation showed that the aroma characters of grapes from different geographical origin were significantly different (P ≤ 0.05). E-2-octenal, styrene and benzaldehyde might serve as the geographical marker compounds of origin area based on the results of GC-IMS analysis and sensory evaluation.

Monoterpenoids Evolution and MEP Pathway Gene Expression Profiles in Seven Table Grape Varieties

This research investigated the evolution of both monoterpenoids and expression profiles of related biosynthesis genes in the MEP pathway in seven different table grape varieties from veraison to maturity stage in two seasons, and the correlation was further evaluated between monoterpenoid accumulation and expression of these genes studied in these varieties. Results showed that linalool, trans-furan linalool oxide, geraniol, and cis-furan linalool oxide were the main compounds in the five Muscat varieties two seasons. ‘Zaomeiguixiang’ had the highest contents of geraniol and β-Citronellol. ‘Xiangfei’ had the most abundant of linalool and cis-furan linalool oxide, whereas the neutral varieties of ‘Moldova’ and ‘Christmas Rose’ had the least amount. Monoterpenoid volatiles have been grouped in three evolutionary patterns in the berry development of these varieties. ‘Zaomeiguixiang’ and ‘Xiangfei’ had distinct different pattern of terpenoids evolution profiles. Pearson’s correlation analysis showed that in the MEP pathway, the first biosynthesis gene VvDXS3 was significantly correlated to the accumulation of monoterpenoids, and appeared to be an important candidate gene for synthesis of the monoterpenoids.

Colored Shade Nets Can Relieve Abnormal Fruit Softening and Premature Leaf Senescence of "Jumeigui" Grapes during Ripening under Greenhouse Conditions

High temperature causes premature grape leaf senescence, abnormal berry softening, and shortening of the fruiting period. Furthermore, the fruit quality and yield are severely affected. Here, the "Jumeigui" grape quality and leaf senescence were evaluated under shading; green, blue, black, and gray nets were used for shading, and their spectra were measured. At the same density, the shade-net color significantly affected cooling and shading efficiencies, with gray nets showing the best light transmission and cooling effect. Shading significantly alleviated abnormal heat-induced grape softness. The total soluble solids (TSS) content and grape coloration were affected under gray, blue, and green shade nets. Nonetheless, TSS exceeded 18 °Brix under gray, blue, and green nets, as required of first-class high-quality fruit. The peel color was not significantly affected under gray or blue shade nets, whereas unshaded grapes showed clear heat-stress damage, especially on the edges of unshaded bottom leaves, in which the net photosynthesis rate was significantly lower than that under shading, indicating that high light intensity and heat caused premature leaf senescence. Colored shade nets reduced greenhouse temperature and light intensity, thereby alleviating the premature senescence of grape plants. Grape quality under black shade nets was poor, whereas superior quality was achieved using gray or blue shade nets.

Effects of Girdling and Foliar Fertilization with K on Physicochemical Parameters, Phenolic and Volatile Composition in ‘Hanxiangmi’ Table Grape

Aroma is one of the most important indicators of grape quality. Girdling and foliar fertilization with K (K2O) are common agronomic practices applied to improve berry quality in grape production. However, little is known about its effect on the accumulation and biosynthesis of the entire aromatic profile. Our study was aimed to explore the influences of girdling and foliar fertilization with K (alone or in combination) on the general properties, phenolic composition, volatile free aroma compounds, spatial and temporal expression of terpene-related genes and sensory properties in ‘Hanxiangmi’ table grape. In this study, we found that girdling and foliar fertilization with K (alone or in combination) facilitated fruit enlargement and increased the accumulation of phenolic compounds in skin. The combination treatment of girdling and foliar fertilization with K significantly promoted the concentrations of total soluble solids (TSS) in the pulp and proanthocyanidins in the berry skin, and had a lower titratable acidity (TA) compared to those of the control. In contrast, girdling treatment alone increased the concentrations of titratable acidity. Volatile free aroma composition analysis revealed that the combination treatment increased the volatile compounds and concentrations significantly, most notably in terpenes, such as nerol, citronellol and linalool. Spatial and temporal expression analysis showed that the expression level of VvDXS was significantly correlated with linalool and total terpenes concentrations, as a result of which, we speculated that VvDXS is the candidate gene for the regulation of important grape terpenes. We hope that our results can direct farmers to better apply girdling and foliar fertilization with K in grape production.

Effects of Berry Thinning on the Physicochemical, Aromatic, and Sensory Properties of Shine Muscat Grapes

The effects of the level of berry thinning (30% and 50% berry removal) on the quality and sensory properties of Shine Muscat grapes were investigated. As berry thinning increased, the total soluble solids content increased and titratable acidity decreased. Berry thinning increased berry size and cluster weight but caused no change in individual berry weight. Phenolic concentrations as measured by total phenolic, proanthocyanidin, and polymeric tannin concentrations tended to increase with an increase in berry thinning. Gas chromatographic analysis indicated that C6-compounds were the significant constituents of volatile alcohols and aldehydes; linalool was the most abundant monoterpene. Odor activity analysis indicated that (E)-2-hexen-1-ol, (E)-2-hexenal, 1-hexanal, (Z)-3-hexenal, (E)-β-damascenone, linalool, and (E)-linalool oxide were active odorants. Berry thinning increased the accumulation of linalool contributing to high sensory flavor scores in thinned berries. Furthermore, its oxidized derivative-linalool oxide-contributed to enhancing the Muscat flavor. In conclusion, berry thinning induced compositional changes in Shine Muscat grape berries by accelerating the ripening rate, contribution to improved sensory properties.

Transcriptomics Integrated with Metabolomics Reveals the Effect of Cluster Thinning on Monoterpene Biosynthesis in 'Muscat Hamburg' Grape

Monoterpenes are crucial to floral and fruit aromas in grapes and wines. Cluster thinning is a common practice for improving grape quality. Using Vitis vinifera cv. Muscat Hamburg, the effects of three cluster-thinning regimes on the biosynthesis and accumulation of monoterpenes from véraison to harvest were investigated at the transcriptomics and targeted metabolomics levels. It was observed that more intense thinning produced higher concentrations of total monoterpenes, particularly in their bound forms. The numbers of differentially expressed genes among the three treatments were 193, 200, and 238 at the three developmental stages. In total, 10 modules were identified from a weighted gene correlation network analysis, and one module including 492 unigenes was associated with monoterpene metabolism. These findings provide new insights into the molecular basis of the relationship between cluster thinning and monoterpene biosynthesis in Muscat Hamburg grape. Cluster thinning could be carefully considered for its application in production.

Early Defoliation Techniques Enhance Yield Components, Grape and Wine Composition of cv. Trnjak (Vitis vinifera L.) in Dalmatian Hinterland Wine Region

Defoliation and cluster thinning are of practical importance in a control of the grapevine source-sink balance, cluster architecture, microclimate and berry composition. Nevertheless, their effectiveness on wine composition is unexplored. In this work, the impacts of preflowering (T1), after berry set (T2), and veraison defoliation (T3) and cluster thinning (T4), on yield components, grape and wine composition of cv. Trnjak are given. Implemented techniques significantly reduced yield and affected grape and wine components in comparison to untreated control (C). Despite lowest number of clusters ensured by cluster thinning, defoliation at veraison had lowest yield. Defoliations improved cluster architecture parameters. Highest berry per se was in preflowering T1 and lowest at veraison T3 defoliation. Berries of T1 had lowest sugar content (19.47 °Brix) while T3 had highest (22.3 °Brix), and the reverse is seen in total acidity highest in T1 (6.12 g/L) and lowest in T3 (5.01 g/L). Wines of early defoliations (T1 and T2) had lowest alcohol and highest anthocyanin concentration. Both techniques applied at veraison produced wines with lower anthocyanins and flavonols than those obtained without any intervention (C). In conclusion, the early defoliations (T1 and T2) improve yield and wine composition of cv. Trnjak in the Mediterranean region of Croatia.