Water status and must composition in grapevine cv. Chardonnay with different soils and topography and a mini meta-analysis of the δ13 C/water potentials correlation

Microbial dysbiosis in roots and rhizosphere of grapevines experiencing decline is associated with active metabolic functions

When grapevine decline, characterized by a premature decrease in vigor and yield and sometimes plant death, cannot be explained by pathological or physiological diseases, one may inquire whether the microbiological status of the soil is responsible. Previous studies have shown that the composition and structure of bacterial and fungal microbial communities in inter-row soil are affected in areas displaying vine decline, compared to areas with non-declining vines within the same plot. A more comprehensive analysis was conducted in one such plot. Although soil chemical parameters could not directly explain these differences, the declining vines presented lower vigor, yield, berry quality, and petiole mineral content than those in non-declining vines. The bacterial and fungal microbiome of the root endosphere, rhizosphere, and different horizons of the bulk soil were explored through enzymatic, metabolic diversity, and metabarcoding analysis in both areas. Despite the lower microbial diversity and richness in symptomatic roots and soil, higher microbial activity and enrichment of potentially both beneficial bacteria and pathogenic fungi were found in the declining area. Path modeling analysis linked the root microbial activity to berry quality, suggesting a determinant role of root microbiome in the berry mineral content. Furthermore, certain fungal and bacterial taxa were correlated with predicted metabolic pathways and metabolic processes assessed with Eco-Plates. These results unexpectedly revealed active microbial profiles in the belowground compartments associated with stressed vines, highlighting the interest of exploring the functional microbiota of plants, and more specifically roots and rhizosphere, under stressed conditions.

Investigating the impact of pedoclimatic conditions on the oenological performance of two red cultivars grown throughout southern Italy

The cultivated grapevine, Vitis vinifera subsp. vinifera, possesses a rich biodiversity with numerous varieties. Each variety adapts differently to varying pedoclimatic conditions, which greatly influence the terroir expression of wine regions. These conditions impact vine growth, physiology, and berry composition, ultimately shaping the unique characteristics and typicity of the wines produced. Nowadays, the potential of the different adaptation capacities of grape varieties has not yet been thoroughly investigated. We addressed this issue by studying two grape varieties, Aglianico and Cabernet Sauvignon, in two different pedoclimatic conditions of Southern Italy. We evaluated and compared the effect of different pedoclimatic conditions on plant physiology, the microbial quality of grapes using Next-Generation Sequencing (NGS) technology, the expression trends of key genes in ripe berries and the concentration of phenolic compounds in grapes and wines by HPLC-MS, HPLC-DAD, NMR and spectrophotometric analyses. Metabolomic and microbiome data were integrated with quantitative gene expression analyses to examine varietal differences and plasticity of genes involved in important oenological pathways. The data collected showed that the phenotypic response of studied grapes in terms of vigor, production, and fruit quality is strongly influenced by the pedoclimatic conditions and, in particular, by soil physical properties. Furthermore, Aglianico grape variety was more influenced than the Cabernet Sauvignon by environmental conditions. In conclusion, the obtained findings not only reinforce the terroir concept and our comprehension of grape's ability to adapt to climate variations but can also have implications for the future usage of grape genetic resources.

Comparing Methods for the Analysis of δ13C in Falanghina Grape Must from Different Pedoclimatic Conditions

Agroforestry applications in viticulture are considered a promising strategy to improve vine water status by mitigating the threats of increasing drought due to climate change. The analysis of δ¹³C is often used in viticulture to understand vine water use. In this study, the analysis of δ¹³C was performed on the must of Falanghina grapevines growing in different pedoclimatic conditions. The aim was to compare the results obtained by the application of two different methodologies, using the whole must or extracted sugars as the matrix. The results showed that the δ¹³C values obtained by applying the two methodologies were comparable in all analyzed vineyards independently from the pedoclimatic conditions. Indeed, the proposed method of extraction of the δ¹³C on the must as a whole can be both cost- and time-saving for the analysis. This is valuable, considering that the δ¹³C of must is becoming more and more used as indicator of vines’ water use. Therefore, the possibility to utilize a simplified method of extraction would enhance the application of the δ¹³C at a larger scale to evaluate vine adaptation in the context of climate-change-driven increases in drought.

Prediction method for determining the carbon stable isotopic composition of berry sugars in the original must of Chardonnay wines

The carbon stable isotopic composition, as indicated by the δ¹³C value, of wine ethanol is inherited from berry sugars, but little is known about the variation in sugar δ¹³C values of Japanese grapes relative to overseas grapes. This study found a large variation in sugar δ¹³C values of Chardonnay grapes grown in Japan (-27.2 ± 0.9‰, mean ± standard deviation, n = 33), with sugar δ¹³C values depending on the δ¹³C values and content of monosaccharides. After complete fermentation, the carbon isotope discrimination between berry sugars and wine ethanol was 1.5 ± 0.1‰. Ethanol δ¹³C values and carbon isotope discrimination enabled prediction of sugar δ¹³C values in the original must. Imported wines had higher sugar δ¹³C values than those of wines made from Japanese grapes, suggesting drier overseas viticulture conditions. The determination of sugar δ¹³C values in grape berries provides valuable information for viticulture and wine authentication.

Water stress assessment on grapevines by using classification and regression trees

Multiple factors, such as the vineyard environment and winemaking practices, are known to affect the development of vines as well as the final composition of grapes. Water stress promotes the synthesis of phenols and is associated with grape quality as long as it does not inhibit production. To identify the key parameters for managing water stress and grape quality, multivariate statistical analysis is essential. Classification and regression trees are methods for constructing prediction models from data, especially when data are complex and when constructing a single global model is difficult and models are challenging to interpret. The models were obtained by recursively partitioning the data space and fitting a simple prediction model within each partition. The partitioning can be represented graphically as a decision tree. This approach permitted the most decisive variables for predicting the most vulnerable vineyards and wine quality parameters associated with water stress. In Priorat AOC, Carignan grapevines had the highest water potential and abscisic acid concentration in the early growth plant stages and permitted vineyards to be classified by mesoclimate. This information is useful for identifying which measurements could most easily differentiate between early and late-ripening vineyards. LWP and Ts during an early physiological stage (pea size) permitted warm and cold areas to be differentiated.

Regulated deficit irrigation strategies affect the terpene accumulation in Gewürztraminer (Vitis vinifera L.) grapes grown in the Okanagan Valley

Regulated deficit irrigation (RDI) is a viticultural practice known to improve grape phenolics and color in red grapes; however, the impact of this practice on grape aromas remains largely unknown. The effects of RDI treatments applied at various berry developmental stages on canopy, yield, and free and glycoside-bound terpenes of the berry were investigated for three consecutive seasons. All RDI treatments reduced leaf photosynthesis and yield, but not when applied after veraison. Berry total soluble solids at harvest were reduced by RDI applied after veraison or throughout the season. Despite reducing berry sugars, RDI applied after veraison increased the concentration at harvest of key free terpenes for Gewürztraminer grapes such as geraniol and citronellol. RDI treatments down-regulated some terpene genes, which indicates that the observed changes in terpene concentration were not transcriptionally regulated. This study suggests that RDI applied after version can potentially improve wine aroma in Gewürztraminer.

Proximal Sensing of Soil Electrical Conductivity Provides a Link to Soil-Plant Water Relationships and Supports the Identification of Plant Water Status Zones in Vineyards

The majority of the wine grapes are grown in Mediterranean climates, where water is the determining factor for grapevine physiology and berry chemistry. At the vineyard scale, plant water status is variable due to the variability in many environmental factors. In this study, we investigated the ecophysiological variability of an irrigated Cabernet Sauvignon (Vitis vinifera L.) vineyard. We used equidistant grid sampling to assess the spatial variations of the plants and soil, including plant water status by stem water potential (Ψ stem ), leaf gas exchange, and on-site soil analysis. We also measured soil electrical conductivity (EC) by proximal sensing at two depths [0.75 - 1.5 m (sub soil); 0 - 0.75 m (top soil)]. Ψ stem integrals were calculated to represent the season-long plant water status. On the base of realized Ψ stem integrals, the vineyard was delineated into two functional homogeneous zones (fHZs) with one severely water stressed zone and one moderately water stressed zone. Sub soil EC was directly related to Ψ stem (r 2 = 0.56) and g s (r 2 = 0.39) when the soil was proximally sensed at harvest in 2018. Although the same trend was evident in 2019 we could not deduce a direct relationship. The fruits from the two fHZs were harvested differentially. Comparing the two fHZs, there was no significant difference in juice total soluble solids or pH. The severely water stressed zone showed significantly higher malvidin and total anthocyanins on a dry skin weight basis, but lower peonidin, malvidin on a per berry basis in 2018. In 2019, there were more quercetin and total flavonols per berry in the severely water stressed zone. Overall, this study provided fundamental knowledge of the viability of managing spatial variability by delineating vineyard into distinct zones based on plant water status, and the potentiality of proximally sensed soil EC in the spatial assessment of plant water status and the supporting of vineyard management.

Distinct Metabolic Signals Underlie Clone by Environment Interplay in "Nebbiolo" Grapes Over Ripening

Several research studies were focused to understand how grapevine cultivars respond to environment; nevertheless, the biological mechanisms tuning this phenomenon need to be further deepened. Particularly, the molecular processes underlying the interplay between clones of the same cultivar and environment were poorly investigated. To address this issue, we analyzed the transcriptome of berries from three "Nebbiolo" clones grown in different vineyards, during two ripening seasons. RNA-sequencing data were implemented with analyses of candidate genes, secondary metabolites, and agronomical parameters. This multidisciplinary approach helped to dissect the complexity of clone × environment interactions, by identifying the molecular responses controlled by genotype, vineyard, phenological phase, or a combination of these factors. Transcripts associated to sugar signalling, anthocyanin biosynthesis, and transport were differently modulated among clones, according to changes in berry agronomical features. Conversely, genes involved in defense response, such as stilbene synthase genes, were significantly affected by vineyard, consistently with stilbenoid accumulation. Thus, besides at the cultivar level, clone-specific molecular responses also contribute to shape the agronomic features of grapes in different environments. This reveals a further level of complexity in the regulation of genotype × environment interactions that has to be considered for orienting viticultural practices aimed at enhancing the quality of grape productions.