Glutathione S-transferase: a candidate gene for berry color in muscadine grapes (Vitis rotundifolia).

Muscadine grapes (Vitis rotundifolia Michx.) are a specialty crop cultivated in the southern United States. Muscadines (2n = 40) belong to the Muscadinia subgenus of Vitis, while other cultivated grape species belong to the subgenus Euvitis (2n = 38). The muscadine berry color locus was mapped to a 0.8 Mbp region syntenic with chromosome 4 of Vitis vinifera. In this study, we identified glutathione S-transferase4 as a likely candidate gene for anthocyanin transport within the berry color locus. PCR and Kompetitive allele-specific PCR genotyping identified a single intragenic SNP (C/T) marker corresponding to a proline to leucine mutation within the muscadine glutathione S-transferase4 (VrGST4) that differentiated black (CC and CT) from bronze (TT) muscadines in 126 breeding selections, 76 cultivars, and 359 progeny from 3 mapping populations. Anthocyanin profiling on a subset of the progeny indicated a dominant VrGST4 action. VrGST4 was expressed in skins of both black and bronze muscadines at similar levels. While nonsynonymous polymorphisms between black and bronze muscadines were discovered in VrGSTF12, another Type I GST-coding gene in the muscadine color locus, this gene was ruled out as a possible candidate for berry color because RNA sequencing indicated it is not expressed in berry skins at véraison from black or bronze genotypes. These results suggest that the bronze phenotype in muscadines is regulated by a mechanism distinct from the MybA gene cluster responsible for berry color variation in Vitis vinifera.

Year, Location, and Variety Impact on Grape-Associated Mycobiota of Arkansas-Grown Wine Grapes for Wine Production.

Wine grape berries (Vitis spp.) harbor a wide variety of yeasts and filamentous fungi that impact grapevine health and the winemaking process. Identification of these fungi could be important for controlling and improving wine production. The use of high-throughput sequencing (HTS) strategies has enabled identification and quantification of bacterial and fungal species in vineyards. The aims of this study were to identify mycobiota from Cabernet Sauvignon and Zinfandel (V. vinifera), Carlos and Noble muscadines (V. rotundifolia), Cynthiana (V. aestivalis), and Vignoles hybrid (cross of different Vitis spp.) grapes, and investigate the effect of grape variety, location, and year on grape fungal communities. Grape berries were collected in 2016 and 2017 from four vineyards located in Arkansas. The HTS of the Internal Transcribed Spacer 1 region was used to identify grape indigenous epiphytic and endophytic fungal communities. The predominant genera identified on the Arkansas wine grapes were Uwebraunia, Zymoseptoria, Papiliotrema, Meyerozyma, Filobasidium, and Curvibasidium. Overall, the data suggested that grape fungal community distribution and relative abundance were influenced by grape variety, year, and location, but each was influenced to a different extent. Not only were grape mycobiota influenced by year, variety, and location but also it appeared that communities from the previous year impacted microbial communities the following year. For example, an increase of the mycoparasite Ampelomyces quisqualis was noticed in 2017 on grapes that carried the causal agent of powdery mildew, Erysiphe necator, in 2016, thus, amplifying the importance of vineyard microbiota knowledge for disease management and winemaking.

Year, Location, and Variety Impact on Grape-, Soil-, and Leaf-Associated Fungal Microbiota of Arkansas-Grown Table Grapes.

With the recent advancement of next-generation sequencing methods, there has been an increase in studies on identification of vineyard microbiota, winery-associated microbiota, and microbiota in wine fermentation. However, there have been few studies investigating the fungal microbiota of table grapes which present distinct spoilage and food safety challenges. The aims of this study were to identify and compare the impact of year, variety, and vineyard location on grape, leaf, and soil fungal communities of two varieties of table grapes, Faith and Gratitude, grown in two open-air vineyards and one high tunnel vineyard. The grape, leaf, and soil mycobiota were analyzed using high throughput amplicon sequencing of the ITS region. The sampling year and location of table grapes had an impact on grape, leaf, and soil mycobiota. Fungal diversity of grape, leaf, and soil was greater in 2017 than in 2016. Grape and leaf samples presented strong similarities in fungal communities with abundance of Sporidiobolaceae and Filobasidium in two vineyards and Cladosporium in another one. The high tunnel structure had distinct grape and leaf fungal communities compared to the two other vineyard locations. Mortierella was the predominant genus (27%) in soil samples for the three locations; however, genera of lower abundance varied between locations. These results provide extensive description of fungal communities in less-studied table grape vineyards and high tunnels, providing useful insight of potential threats and preventive strategies to help improve the production and marketability of table grapes.

Analysis of wine components in Cynthiana and Syrah wines.

Red wine is composed of a complex matrix of compounds that can interfere with analysis. A high-performance liquid chromatography (HPLC) procedure was developed to efficiently analyze organic acids, sugars, glycerol, and ethanol in Cynthiana (Vitis aestivalis) wine. Standard laboratory procedures (pH, titratable acidity, and color attributes) and HPLC were found reproducible for Cynthiana wine. HPLC recovery efficiency was determined by analysis of spiked and unspiked samples (model, Cynthiana, and Syrah (Vitis vinifera) wines). Although recovery of components was greater in the model wine, recovery in Cynthiana and Syrah wine was comparable. The HPLC procedure was further compared to commercial rapid enzyme analysis tests using model, Cynthiana, and Syrah wines. HPLC analyses were more accurate than enzymatic tests for determining components in the model, Cynthiana, and Syrah wines. Considering the complexity of the wines analyzed, reproducibility and recovery of the HPLC procedure was demonstrated and showed improvement and precision when compared to existing methods.

pH modification of Cynthiana wine using cationic exchange.

Membrane and resin ion-exchange technology was used for pH reduction and production of Cynthiana (Vitis aestivalis) wine, which can have high pH and high titratable acidity. Wine attributes were monitored during storage for 6 months at 21 and 38 degrees C. Nonadjusted Cynthiana wine (pH 4.1) was compared to ion-exchange-adjusted wine (pH 3.5). Ion exchange lowered the pH and potassium content and increased the titratable acidity of wine without having detrimental effects on color and phenolics. No trends were found to indicate differences between manufacturers of membranes and resins on pH-adjusted Cynthiana wine. Wine treated with membrane ion exchange was higher in color density and phenolics than resin-treated wine. During storage at both temperatures, the quality of the wine decreased, with greater degradation at 38 degrees C. Ion exchange decreased the pH of Cynthiana wine without negatively affecting wine quality attributes. A panel familiar with characteristics of Cynthiana wine found that the color and flavor of the pH-adjusted wine was improved.