Grape Maturity Research Articles

Populations of Saccharomyces cerevisiae in Vineyards: Biodiversity and Persistence Associated with Terroir

The origin terroir provides distinctive characteristics for wines, in relation to soil, climate, oenological practices, etc. Hence, the characterization of each wine region by multiple aspects would allow differentiation of its wines. Several approaches at different scales have studied terroir microbiological fingerprints: from global microbiome analysis up to intraspecific Saccharomyces biodiversity. Mature grapes are the primary source of yeasts, and S. cerevisiae is a key wine fermentative species. Malbec is the emblematic Argentinean variety and is mainly cultivated in the “Zona Alta del Rio Mendoza” (ZARM). In this work, the diversity of S. cerevisiae grape populations was studied at three vintages in two Malbec vineyards of the ZARM, to evaluate their annual diversity and behavior in different vintages. Rarefaction of classical ecological indices was applied for a statistically adequate biodiversity analysis. A total of 654 S. cerevisiae isolates were differentiated by Interdelta-PCR. Each yeast grape population showed a unique composition of S. cerevisiae strains; however, a narrow genetic relationship was found in each vineyard. A slight increase in the initial diversity and a stabilization in the diversity of S. cerevisiae populations were confirmed. These results add to the discussion about the contribution of yeasts to the terroir microbiological concept, and its limitations and stability over the time.

Assessment of Variability Sources in Grape Ripening Parameters by Using FTIR and Multivariate Modelling.

The variability in grape ripening is associated with the fact that each grape berry undergoes its own biochemical processes. Traditional viticulture manages this by averaging the physicochemical values of hundreds of grapes to make decisions. However, to obtain accurate results it is necessary to evaluate the different sources of variability, so exhaustive sampling is essential. In this article, the factors "grape maturity over time" and "position of the grape" (both in the grapevine and in the bunch/cluster) were considered and studied by analyzing the grapes with a portable ATR-FTIR instrument and evaluating the spectra obtained with ANOVA-simultaneous component analysis (ASCA). Ripeness over time was the main factor affecting the characteristics of the grapes. Position in the vine and in the bunch (in that order) were also significantly important, and their effect on the grapes evolves over time. In addition, it was also possible to predict basic oenological parameters (TSS and pH with errors of 0.3 °Brix and 0.7, respectively). Finally, a quality control chart was built based on the spectra obtained in the optimal state of ripening, which could be used to decide which grapes are suitable for harvest.

Grapevine red blotch virus alters grape skin cell-wall composition impacting phenolic extractability during winemaking.

Grapevine red blotch virus (GRBV) is the causal agent of grapevine red blotch disease and is known to delay grape ripening. However, grape cell-wall modifications during GRBV infection are largely unknown, even though the cell wall plays a large role in pathogenicity, viral interactions with host plants, and phenolic extractability during winemaking. Understanding the impact of GRBV infection on cell-wall metabolism is important for the development of potential mitigations strategies. In this study, high-throughput transcriptome sequencing was conducted on Vitis vinifera L. 'Merlot' grapes during ripening. The cell-wall composition, phenolic content, and phenolic extractability at two different commercial harvest points were also determined. Log fold changes indicated a strong induction in diseased grapes at harvest of several transcripts involved in cell-wall solubilization and degradation. However, these observations did not translate to changes in cell-wall composition at either harvest point in diseased grapes, potentially suggesting post-transcriptional regulation. Moderate induction of pectin methylesterase inhibitor transcripts and transcripts associated with pathogenesis-related proteins coincided with increases in pectin and soluble proteins in cell walls of diseased grapes at harvest. Both pectin and pathogenesis-related proteins are known to retain phenolic compounds during winemaking. Our study corroborates this finding when the percentage extractability of flavonols in wines was significantly lower when made from GRBV-infected fruit. These results suggest GRBV alters the grape cell walls, consequently decreasing phenolic extraction during winemaking. © 2023 Society of Chemical Industry.

Evaluation of the Carry-Over Effect of the “Crop-Forcing” Technique and Water Deficit in Grapevine ‘Tempranillo’

“Crop-forcing” is an effective technique to delay grape maturation to a period of lower temperatures, and in this way, improve grape quality. Because of the aggressiveness of this technique (removal of leaves and fruit to reinitiate a second vegetative cycle), it may affect the level of reserves and could provoke progressive vine exhaustion. The aim of the present work is to evaluate the short- and medium-term evolution of carbohydrate reserves in different plant organs and the effect of “crop-forcing” under different irrigation regimes on seasonal biomass production and its distribution. The study was carried out over a four years period (2017–2020), applying “crop-forcing” in three consecutive years (2017–2019) to the same vines on two different dates and using two irrigation strategies. The application of “crop-forcing” did not decrease root reserve levels in either the year of application or the following year, but did modify starch and soluble sugar levels in shoots and leaves in some moments of the vegetative cycle during the years of “crop-forcing” application. Total biomass production in terms of grams per vine was lower in the “crop-forcing” treatments and continued to be so when “crop-forcing” was no longer applied. The percentage of biomass in vegetative organs increased at the expense of productive organs.

Use of unripe grape wine as a tool for reducing alcohol content and improving the quality and oenological characteristics of red wines

In Mediterranean viticulture, climatic conditions are the main factors that determine grape composition and wine quality. Global warming is causing an increase in the accumulation of soluble solids in grapes, leading to early harvests that result in wines with high alcohol and low phenolic content and colour intensity. The aim of this research was to determine the effectiveness of mixing wines vinified from grapes with different maturation degrees from two consecutive vintages (2018 and 2019) in order to obtain wines with lower pH, lower alcohol content and higher phenolic compound concentration. The wine obtained after mixing wine from unripe grapes (URG) with second harvest (H2) wines significantly improved the physicochemical, chromatic and phenolic characteristics compared to the first harvest (H1) wine. On the other hand, the URGH2 wine had significantly lower alcohol content and pH and higher titratable acidity than the H2 wine. URGH2 maintained its colour intensity in both years and similar values of anthocyanin and tannin in 2018 compared to H2. All the wines were subjected to sensory analysis and the panelists were able to differentiate the wines in a triangle sensory test; the URGH2 wine was preferred in both years. These results show that the blend of unripe grape with wines from technologically mature grapes to reduce alcohol content and improve wine colour could be a useful tool for mitigating the problems caused by global warming in a warm and semiarid Mediterranean climate.

Estimation of Sugar Content in Wine Grapes via In Situ VNIR-SWIR Point Spectroscopy Using Explainable Artificial Intelligence Techniques.

Spectroscopy is a widely used technique that can contribute to food quality assessment in a simple and inexpensive way. Especially in grape production, the visible and near infrared (VNIR) and the short-wave infrared (SWIR) regions are of great interest, and they may be utilized for both fruit monitoring and quality control at all stages of maturity. The aim of this work was the quantitative estimation of the wine grape ripeness, for four different grape varieties, by using a highly accurate contact probe spectrometer that covers the entire VNIR-SWIR spectrum (350-2500 nm). The four varieties under examination were Chardonnay, Malagouzia, Sauvignon-Blanc, and Syrah and all the samples were collected over the 2020 and 2021 harvest and pre-harvest phenological stages (corresponding to stages 81 through 89 of the BBCH scale) from the vineyard of Ktima Gerovassiliou located in Northern Greece. All measurements were performed in situ and a refractometer was used to measure the total soluble solids content (°Brix) of the grapes, providing the ground truth data. After the development of the grape spectra library, four different machine learning algorithms, namely Partial Least Squares regression (PLS), Random Forest regression, Support Vector Regression (SVR), and Convolutional Neural Networks (CNN), coupled with several pre-treatment methods were applied for the prediction of the °Brix content from the VNIR-SWIR hyperspectral data. The performance of the different models was evaluated using a cross-validation strategy with three metrics, namely the coefficient of the determination (R2), the root mean square error (RMSE), and the ratio of performance to interquartile distance (RPIQ). High accuracy was achieved for Malagouzia, Sauvignon-Blanc, and Syrah from the best models developed using the CNN learning algorithm (R2>0.8, RPIQ≥4), while a good fit was attained for the Chardonnay variety from SVR (R2=0.63, RMSE=2.10, RPIQ=2.24), proving that by using a portable spectrometer the in situ estimation of the wine grape maturity could be provided. The proposed methodology could be a valuable tool for wine producers making real-time decisions on harvest time and with a non-destructive way.

Climate Effect on Morphological Traits and Polyphenolic Composition of Red Wine Grapes of Vitis vinifera

Wine quality is determined by the development of grape maturation, which is highly dependent on climate variations. Extreme weather events are becoming more common, which will affect the productivity and quality of grapes and wine. Grape development depends on many factors, including weather, and extreme events will influence berry size, skin thickness and the development of some key compounds, such as phenolics. In this work, the ripening evolution and phenolic content of Vitis vinifera extracts from a vineyard in Alentejo (Portugal) were evaluated in two distinct climatic years. During this period, the influence of climatic conditions on grape ripening, and thereby on red wine quality, was assessed. The results demonstrate differences in polyphenol compounds between years and the importance of monitoring their content during maturation. The reduction of berry size, apparently due to lower pluviosity and higher temperatures, resulted in a higher content of polyphenolic compounds related to grape quality.

Canopy management through crop forcing impacts grapevine cv. ‘Touriga Nacional’ performance, ripening and berry metabolomics profile

Climate changes are speeding up the maturation of grapes in numerous areas of the world, including in the Mediterranean basin, but warmer temperatures often uncouple technical and phenolic maturity, resulting in unbalanced wines. We tested the efficacy of crop forcing (CF) in delaying the maturation of cv. ‘Touriga Nacional’ vines of the Douro Region, and their impacts on plant performance, berry quality attributes and metabolome were also evaluated. In two consecutive seasons (2019 and 2020), CF was conducted 15 (CF1) and 30 (CF2) days after fruit set by hedging growing shoots to five nodes and removing summer laterals, leaves and clusters. Results showed that while CF2 delayed ripening up to 51 days till first autumn rainfall, which compromised optimal sugar ripeness, CF1 delayed the technical maturation by one month, but both treatments severely impacted the production, mainly CF1, which reduced grapevine yield up to 90 %. The effect of CF in protecting vines against drought stress was not evident, judging by the values of leaf pre-dawn water potential measured along both seasons. CF1 and CF2 resulted in berries with lower pH and higher titratable acidity than controls, while total phenolics content increased by up to 48 % in 2020. A UPLC–MS-based targeted metabolomic analysis showed that CF increased the relative abundance of key metabolites like flavan-3-ols (i.e., catechin gallate increased by up to 661 %), trihydroxylated anthocyanins (i.e., delphinidin-3-O-glucoside increased by up to 656 % after CF2) and stilbenes (resveratrol increased by up to 700 % after CF2) with potential positive impacts in wine quality.

Understanding the Sensitivity of Grape Terpenes to Jasmonates Using In Vitro Culture and In Vivo Vineyard Experiments.

Terpene volatiles define the flavor of terpenic grape cultivars. However, grape terpene concentrations can vary 2- to 3-fold across seasons and vineyards, impacting vintage quality. The plant hormone methyl jasmonate (MeJA) stimulates grape terpene production but is expensive and can decrease berry weight and maturity. The synthetic jasmonate prohydrojasmon (PDJ) is cost-effective yet has not been evaluated on grape maturity and terpene production. Here, we performed in vitro (berry culture) and in vivo (vineyard) experiments using Gewürztraminer (Vitis vinifera L.) to evaluate the time- and concentration-dependent sensitivity of maturity parameters and terpene content to MeJA and PDJ. In vitro berry weight was reduced by high MeJA and PDJ concentration across timings. Terpenes were most sensitive to low MeJA concentration at veraison (increased 24-fold) in vitro. Moderate PDJ concentration applied at veraison doubled (increased twofold) terpene concentration in vivo without impacting berry weight or maturity. In conclusion, PDJ may provide a solution to mitigate seasonal variability in terpene production in terpenic grape cultivars.

Ethylene accelerates grape ripening <i>via</i> increasing <i>VvERF75</i>-induced ethylene synthesis and chlorophyll degradation

Ethylene plays an important role in grape ripening, acting through ethylene response factors (ERFs) that are downstream of ethylene signaling pathways, yet little else is known about these molecular mechanisms. In our study, we demonstrate that ethylene treatment promotes grape ripening and that the transcription factor <italic>VvERF75</italic> shows increased expression during grape ripening. <italic>VvERF75</italic> was found to contain a conserved AP2/ERF domain, to be a member of the ERF IXa subfamily, an to localize to the nucleus and to have transactivation activity in yeast. Our in vitro assays showed that <italic>VvERF75</italic> can positively regulate expression of <italic>pheophorbide</italic> a<italic> oxygenase</italic> (<italic>VvPAO1</italic>) and <italic>1-aminocyclopropane-1-carboxylic acid synthase</italic> (<italic>VvACS5</italic>) by binding to DRE motifs in their promoters. Overexpression of <italic>VvERF75</italic> in tomato increased ethylene production and resulted in dwarfed plants, early flowering and fruit ripening, increased <italic>SlPAO</italic> and <italic>SlACS</italic> transcript levels, and decreased chlorophyll content. In general, our study revealed that <italic>VvERF75</italic> may regulate fruit ripening by promoting ethylene biosynthesis and chlorophyll degradation, a discovery that lays a foundation for deciphering the molecular mechanisms of grape ripening.

Assessment of grape volatile composition using fluorescence indices of leaves in vineyards affected by iron chlorosis

Multiplex 330 (MX) is a portable, non-invasive fluorescence sensor that provides different multiparametric indices that are sensitive to the concentration of chlorophylls, flavonols, and anthocyanins on the leaf surface. This study investigated the use of these indices to assess the variability on free volatile composition of grapes (Vitis vinifera L.) in the field as well as other components of their quality potential in vineyards affected by iron deficiency chlorosis (IDC). Twenty non-irrigated Tempranillo/110 Richter vineyard subzones from non-affected to moderately affected by IDC were monitored in Ribera del Duero area (Spain) during two seasons. The results indicated that MX can characterize the spatial variation of leaf pigment concentrations, agronomic performance, and grape quality in vineyards affected by IDC. The MX indices measured at the leaf level close to harvest had better predictive values for the concentrations of free alcohols, volatile acids, C13-norisoprenoids, esters and acetates in the must than vine vigor, size or degree of technological maturity of the grapes. Our study demonstrates that the MX indices to estimate leaf pigment concentrations can be helpful to assess the technological maturity and free volatile composition of wine grapes in vineyards affected by IDC; nevertheless, the efficacy of the indexes may vary according to the year season.

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The aim of the work is to study the growing dynamics of total sugars, acids and phenolic compounds (flavonoids, anthocyanins) in Sev Areni grape berries in conditions of organic farming depending on the buds’ load rate. The studies were conducted in 2020-2021. The vineyard belonging to “Hin Areni” CJSC, established in 2007-2008, is located in the Areni community of Vayots Dzor marz, at an altitude of 1200 m above sea level. At the start of the trials, 5 hectares of the garden (10 ha) were cultivated with organic methods. The experiments were carried out in four replications through the method of Lazarevskiy including 15 vines in each option. The dynamics of berry ripening was studied according to vine load. Sugar content (refractometric method), titratable acidity (using OIV-MA-AS313-01 method), pH, total phenolic content of fruit juice was determined three times. According to study results, the amount of flavonoids and anthocyanins changes during grape ripening, depending on the vine load. Along with the grapes maturation, sugar content of the fruit juice increases, the acidity decreases. However, parallel to the increase in vine load, the sugar content decreases. In the option of 50 bud load the sugar content decreases. The harvested yield lags behind the option of 30-40 bud load in its qualitative properties. Thus, it is not recommended to use high bud loading option in the organic farming. Based on the study results, it is recommended to use 30-40 bud vine loads of Sev Areni variety in conditions of vineyards organic farming.

Role of foliar biostimulants (of plant origin) on grapevine adaptation to climate change

Heat waves and drought stress are typical aspects of current climate change, significantly affecting the grapevine physiology in many world growing areas. Biostimulants can play an important role in reducing the negative effects of climate change; that’s why this experiment was set up in order to test two new foliar biostimulants (protein hydrolysates of plant origin). The field experiment was carried out in 2017 and 2018 in Oltrepo pavese area (Lombardia region, northwest Italy, 270 m asl), on a six-year-old vineyard of V. vinifera L. cv. Merlot clone 181 grafted on Gravesac, Guyot trellis, 4,000 vines/ha and not irrigated. Two new protein hydrolysates of plant origin were sprayed twice, just after fruit set and 15 days later, by using 2.5 L/ha. Leaf proteomics and metabolomics were studied in 2017, while productive and qualitative data were recorded in both years at harvest (September 1st, 2017 and August 28th 2018). The most significant findings were: (a) the treatments slowed down the grape ripening, by stimulating vegetative activity and reducing sugar accumulation; (b) less heat and drought stress symptoms were observed in the canopies of treated vines, as compared to the control ones.

Foliar Fertilizers as A Method Of Phenolic Ripeness Control

Due to global warming, there is a problem to correlate technical and phenolic ripeness in modern viticulture. This study is focused on the use of foliar fertilizers in order to combine the time of beginning of phenolic and technical ripeness. The studies were carried out in 2022 in the conditions of mountain-valley coastal viticulture zone of the Republic of Crimea. Foliar top dressing was carried out with the preparation ‘Agrogemo’ (LLC Pontis, Russian Federation) on wine grape varieties ‘Bastardo Magarachskiy’ and ‘Malbec’. The Glories method was used to estimate the ripeness degree of grapes. The principle of it is to determine the total and extractable anthocyanin potential of grapes. Using of foliar fertilizers made it possible to increase the yield of ‘Bastardo Magarachskiy’ variety by 15.3%, and ‘Malbec’ variety by 18.1%. It was found that the experimental treatment scheme contributed to the later beginning of technical ripeness of grapes, i.e. a low percentage of non-extractable anthocyanins from grape skin compared to the control. Base wines obtained from grapes with the use of organic-mineral fertilizer were characterized by the intense color, balanced aroma and flavor.

Influence of grapevine age on general physicochemical and phenolic parameters of Rabigato (Vitis viniferaL.) white variety: Results from three vintages

The preservation of the old vine heritage, combined with the fact that old vines could present greater resistance to biotic and abiotic factors, has led to an increase in research studies about the contribution of vine age on grape and wine quality. Thus, the main goal of this work was to evaluate the potential influence of grapevine age on several general physicochemical and phenolic parameters during grape maturation of a Rabigato white grape variety. Therefore, grapes from two adjacent vineyards, with an age difference of 30 years (one with 20 years and the other with 50 years, at the beginning of this study) were studied. At technological maturation, the results obtained for the three consecutive vintages studied (2019 to 2021), and for the general physicochemical parameters analysed, do not seem to indicate a clear differentiation between the grape musts obtained from the younger and the older vineyards. However, for grape phenolics, the results suggest that vine age could be a potential factor on phenolic content, nevertheless not totally confirmed by the results at technological maturation during the three consecutive vintages considered. With this work we will contribute to expand the knowledge about the potential impact of the vine age on grape composition.

Impact of climate change on grape cluster structure, grape constituents, and processability

Over the last 20 years in the Pfalz region of Germany, GDD were highest in the vintages 2018-2020. To visualize the effect of climate change for the Pfalz region of Germany, the development of TSS and TAwere documented during Pinot noir grape ripening for the vintages 1998-2021. It was observed that climate change causes sooner and accelerated ripening, however, sooner or accelerated ripening were not connected with each other. The presented study investigated the impact of vintages on berry physiology development, ripening heterogeneity in grape clusters, changes in grape constituent concentrations and their extractability with progressing grape maturity. Pinot noir and Cabernet Sauvignon, both cultivated in the Pfalz region, were compared during three consecutive vintages. Different maturities were considered in the range of 17-25 Brix and berry size distribution was documented. The changes in grape constituent concentrations and their extractability with progressing grape maturity were analyzed using HPLC-DAD/FD, LC-QToF-MS and protein precipitation assay. It was revealed that tannin extractability differs for grape varieties and vintages and progressing maturity seemed to have only a small influence on the extractability of anthocyanins.

Phenolic compounds extractability from Melnik 55 grape solid parts during fruit maturity

Samples from Melnik 55 grape variety (Vitis vinifera) were collected from different stage of grape maturity. Grape seeds and skins from each sample were separated and extracted with model wine solutions with increasing alcohol content simulated alcohol accumulation during wine fermentation. Total phenolic compounds, anthocyanins, skin pigments and tannins in each sample were determined. During grape ripening not only total phenols content of grape skins and seeds are changed but also their extractability. Ethanol released during wine fermentation is strong phenol extragents but its role is getting smaller as riper is the grape. This tendency is more pronounced in seeds phenolics extractability than in skins.

The relative copy number of mitochondrial and chloroplast DNA in young and mature leaves of different grape varieties

The copy number of DNA matrices of subcellular organelles (plants) can serve as an indicator of the intensity of photosynthesis and oxidative phosphorylation processes. We assessed the relative copy numbers (RCN) of mitochondrial and chloroplast DNA in young and mature leaves of three grape varieties: ‘Traminer Pink’, ‘Chardonnay’, and ‘Syrah’, grown under field conditions. Leaf samples (5–10 mg) were randomly selected from each group of plants for subsequent total DNA extraction. The qRTPCR reaction was performed using LightCycler 480 SYBR Green I Master Mix (LifeScience, Roche) and a LightCycler 96 Automatic Analyzer (Roche Life Science). The relative copy numbers of the NAD1 gene (mitochondrial DNA) and rps16 gene (chloroplast DNA) were determined using the GAPDH gene (chromosomal DNA) as a reference. Quantitative assessment was conducted using the 2--Ct и 2---Ct algorithms. It has been established that the relative copy number (RCN) values of chloroplast and mitochondrial DNA vary and depend on the grape variety and leaf maturity. RCN of chloroplast and mitochondrial DNA is significantly higher in mature grape leaves of all studied varieties, indicating a higher intensity of photosynthesis and oxidative phosphorylation in mature grape leaves compared to young leaves. When assessing the MacroErgic Balance (MEB) indicator, it can be concluded that from 2 to 4% of the energy obtained in chloroplasts through photosynthetic processes is used for the production of macroergic compounds in the mitochondria of various grape varieties in both young and mature leaves. The experimental scheme we have developed can be successfully used as a testing system to assess the potential yield of various grape varieties.

Multi-criteria decision analysis integrated with GIS to determine land suitability for cultivation and best harvest time of vine.

In this study, the quality of land suitability for vine cultivation in south-western Iran was evaluated and a land suitability map for vine cultivation was developed using the fuzzy-analytic hierarchy process (AHP). The best harvest time of vines was determined based on the relationship between total soluble solids (TSS) and titratable acidity (TA) with fruit colour (red, green, and blue or RGB) in ten points and also the growing degree-days (GDD) maps from April to December. The relationship between GDD and effective parameters in vine cultivation was determined using principal component analysis (PCA) and Pearson correlation methods. The results illustrated that the maximum temperature and relative humidity (RH) have the greatest effect on vine cultivation and its yield (weight 0.24). The results of the land suitability map showed that central regions have better conditions for growing vines (32%). The measurements of TA and TSS depicted that vines of the northern parts have higher TA and lower TSS and there is a significant relationship between them and fruit colour. The results of GDD maps showed that the harvest time of ruby vine and Gezel-azm is July and August, respectively. Also, the temperature (Tmean , Tmax and Tmin ), wind speed, and GDD were the most important parameters to determine the best location for vine cultivation. Determining land suitability for cultivation, the best harvest time, the time of grape ripening, and following the exact time of export and import of vine has a vital role to increase its productivity and services. © 2022 Society of Chemical Industry.

HDAC19 recruits ERF4 to the MYB5a promoter and diminishes anthocyanin accumulation during grape ripening.

DNA acetylation alters the expression of responsive genes during plant development. In grapes (Vitis vinifera), however, little is known about this regulatory mechanism. In the present study, 'Kyoho' grapes treated with trichostatin A (TSA, a deacetylase inhibitor) were used for transcriptome sequencing and quantitative proteomics analysis. We observed that acetylation was associated with anthocyanin accumulation and gene expression. Acetylation positively regulated phenylalanine metabolism and flavonoid biosynthesis pathways. Using omics analysis, we detected an increase in the levels of the AP2/EREBP transcription factor family after TSA treatment, indicating its association with acetylation-deacetylation dynamics in grapes. Furthermore, ethylene response factor 4 (ERF4) physically interacted with VvHDAC19, a histone deacetylase, which synergistically reduced the expression of target genes involved in anthocyanin biosynthesis owing to the binding of VvERF4 to the GCC-box cis-regulatory element in the VvMYB5a promoter. VvHDAC19 and VvERF4 also controlled anthocyanin biosynthesis and accumulation by regulating acetylation levels of histones H3 and H4. Therefore, alterations in histone modification can significantly regulate the expression of genes involved in anthocyanin biosynthesis and affect grape ripening.