Vitis genetic resources: current challenges, achievements and perspectives

Management and knowledge of Vitis genetic resources aim to help address the multiple current and future challenges facing the professional sector: i) preservation of wild and cultivated grapevine heritage, ii) clonal selection of existing cultivars, iii) creation of new cultivars by hybridisation or other technologies, iv) progress in fundamental and applied sciences on all viticultural and oenological issues. It is therefore a vast field of study and actions that deals with all taxonomic levels within the Vitis genus (subgenus, species and their hybrids, cultivars and their variants, clones), in natural and cultivated environments, on all continents, both for fruit production (wine and table grapes) and for rootstocks. To meet the many expectations, different actors should ideally coordinate the following actions: 1) research and identification of sources of genetic diversity, 2) access, collection and sampling of this diversity, 3) ex situ and/or in situ conservation, 4) characterization, 5) dissemination of plant material and related information, 6) use of genetic resources by the different applicants. Following this outline, we will try to assess the challenges and achievements over the last 5-10 years, and discuss the perspectives of this disciplinary field taking into account elements of the wine-growing, scientific, institutional and regulatory context

Single berry development – a new phenotyping and transcriptomics paradigm

Most present knowledge on berry development has been obtained from a random sampling of hundreds of berries to average their diversity of the experimental plot. According to recent studies, such heterogeneous samples formed from non-synchronized berries of mixed developmental stages are unsuitable for detecting fast physiological and molecular changes. Thus, it is necessary to revisit the physiological and transcriptional bases of berry ripening. Here we report the in-depth study of the late-ripening program in three genotypes. Berry expansion during the second growth phase was characterized on-vine through image analysis. Hundreds of sampled berries were individually analyzed for primary metabolites to calculate their respective accumulation rates with high precision. These primary individual fluxes and the growth kinetics allowed us to distinguish targeted developmental stages further investigated through RNA profiling. Single berry monitoring evidenced sharp developmental phases during which specific genes or pathways are quickly switched ON or OFF. The comparison between Syrah and the two microvines showed phenotypic differences in late-ripening stages in vines grown in the field (Syrah) and microvines (MV032 and MV102) grown in the greenhouse. This study shows that new high-throughput single berry phenotyping methods are required to compare unambiguous developmental stages in physiological or genetic studies

Evaluation of glutathione content in white grape varieties

The aim of this work was to evaluate the content of glutathione in the grape, must and wine of nine white varieties authorized in the Qualified Designation of Origin Rioja (Spain): 'Chardonnay', 'Garnacha Blanca', 'Malvasía', 'Maturana Blanca', 'Tempranillo Blanco', 'Turruntés', 'Sauvignon Blanc', 'Verdejo' and 'Viura'. The results obtained showed important varietal differences in the concentration of GSH. 'Sauvignon' and 'Tempranillo Blanco' presented high levels of this compound in grape, must and wine. 'Verdejo' and 'Turruntés' registered high values in grape, which decreased notably in must and wine. In general, the GSH content decreased in musts due to oxidative processes. In 'Chardonnay', 'Garnacha Blanca', 'Maturana Blanca' and 'Viura' an increase was observed in wines, which could be caused by the inoculated yeast. The 'Malvasía' and 'Maturana Blanca' varieties registered the lowest level of this compound. The ratio of hydroxycinnamic acids to glutathione, indicator of the susceptibility of oxidation of musts, showed significant varietal differences, was lower in 'Sauvignon Blanc' and higher in 'Garnacha Blanca'

Tannin content and antioxidant capacity of five Greek red grape varieties

Tannins are located in skins and seeds and are responsible for important sensory and quality attributes of red grapes and wines, such as astringency, bitterness and colour stability. However, little is known regarding Greek Vitis vinifera varieties. The aim of this study is to evaluate the grape phenolic content and to present data that may contribute to the development of suitable winemaking techniques for these varieties. In this study berry attributes, skin and seed content of tannins and antioxidant capacity from five Greek Vitis vinifera varieties, namely 'Mavrotragano', 'Mandilaria', 'Kotsifali', 'Agiorgitiko' and 'Xinomavro' were analyzed. Significant differences were observed in berry weight and the distribution of berry component mass in mature berries, among the different varieties. 'Mandilaria' and 'Kotsifali' had the heavier berries while the higher contribution of skins and seeds in berry was observed in 'Agiorgitiko' and 'Mavrotragano' grapes respectively. According to the results, the higher content of seed tannins in berries was determined in 'Mandilaria' and the lower in 'Kotsifali'. Finally, varieties with high concentrations of tannins, 'Mandilaria' and 'Mavrotragano', also demonstrated significant high values of antioxidant capacity

Evolution of antioxidant capacity in seeds and skins during grape maturation and their association with proanthocyanidin and anthocyanin content

In order to investigate the antioxidant activity in seeds and skins during grape maturation and their relation with anthocyanin and proanthocyanidin content, two Portuguese red grape varieties, 'Touriga Nacional' and 'Tinta Roriz' were studied. For antioxidant activity analysis, one analytical method was used (ABTS method). Different proanthocyanidins fractions according to their degree of polymerization were analyzed, while 13 different individual anthocyanins were evaluate by HPLC as well. During the maturation period the antioxidant activity content quantified from the different grape berry fractions was characterized by a general decrease with a slight oscillation in the early stages of maturation, followed by a stabilization and slight increase of the values in the last weeks of ripening. Similar evolution was observed for the different proanthocyanidins fractions quantified. For the individual anthocyanins, in general the evolution was characterized by a slowly increase in the first 3 weeks of ripening process, followed by a marked increase and finally a slight decrease or stabilization in the last weeks of ripening. Finally, high linear positive correlations between proanthocyanidin fractions and the antioxidant activity evolution during the grape maturation were obtained while for the individual anthocyanins a high negative correlation values was quantified

Relationship between meteorological data, physical-mechanical characteristics of grapes and Botrytis bunch rot

Botrytis bunch rot (BBR) is the economically third most important disease in cool climate viticulture. In order to avoid or delay spreading of BBR infections until the grapes reach physiological ripeness, different management strategies like early defoliation or specific fungicide applications were developed. The scope of most grapevine breeding programs is the selection of mildew fungus-resistant, climatic adapted grapevines with balanced, healthy yield and outstanding wine quality. Within the long-term breeding process, the application of marker-assisted selection (MAS) is the most efficient way for early selection of desired grapevine seedlings. Since no resistances have yet been described for BBR, grapevines shall be selected for developing fruits with physical-mechanical barriers reducing the risk for BBR infection like loose grape bunch architecture and thick, impermeable berry cuticle. In the present study first results regarding the investigation of the relationship between physical-mechanical fruit traits (bunch architecture, berry impedance and berry texture), meteorological data and the degree of BBR infection are shown. Varieties and elite breeding lines were phenotyped using high-throughput, objective sensors in 2021 and 2022, two years with contrasting growing conditions (Siebeldingen, Germany). In comparison to 2021, 2022 was characterized by a higher temperature sum D (+196°days between veraison and harvest) and huge differences in the precipitation sum (PS; -62 mm up to + 105 mm). In order to categorize BBR resistance/ susceptibility, berries from different genotypes showing high variability in their berry characteristics were sampled at maturity and were tested under controlled lab conditions for BBR susceptibility. For some varieties, it could be shown that meteorological conditions affect both, berry traits as well as infection with BBR. In addition to the environment and the training system, physical-mechanical berry traits and the mean berry diameter could be confirmed as promising phenotypic traits for the prediction of BBR resistance. In summary, the consideration of sensor-based physical-mechanical berry traits enables an improved risk prediction for BBR, which is of outstanding importance for the evaluation of breeding material and new varieties growing under different environmental conditions, as well as for phenotyping of mapping populations for QTL analyses and the development of molecular markers. As meteorological conditions were contrasting in 2021 and 2022 and varieties with high phenotypic variability were considered, additional years of investigations are recommended in order to verify the reliability of the detected relationships

Uncovering Northeast Portugal grapevine's varietal legacy

Northeast Portugal comprises the wine denominations "Douro" and "Trás-os-Montes". There are more than one hundred grapevine cultivars registered suitable for wine production in these regions (ministerial-orders number 1204/2006 and 383/2017), however only a few are actually used for winemaking. In this sense, the identification of the varieties cultivated in past times may widen the number of varieties and can be an important step to take advantage of all the potential of these regions' grapevine biodiversity. The conservation of these vanishing genetic resources boosts a greater products' diversification and it can be considered strategic in the improvement and valorization of "Douro" and "Trás-os-Montes" PDO wines. Moreover, it is imperative to identify, before to characterize and preserve, plants of late-maturing grape varieties planted in regions with extremely high temperatures and precipitation deficits which still maintain grape yield and produce very well-known quality wines. Hence, the main goals of this study were to prospect and characterize, through nuclear and chloroplast SSR analysis, plants of old vineyards that constitute a broad representation of the grapevine genetic patrimony of "Douro" and "Trás-os-Montes" regions

Do we need to consider grape phyllosphere microbiome in breeding schemes?

The aerial surface of the plant (phyllosphere) is the habitat of complex microbial communities. These communities may have profound effects on host plant health and its performance traits. When breeding new cultivars, i.e. the aerial component of a grape plant, one can simply ignore the phyllosphere in breeding schemes if its composition is mainly dependent on the environment. It is considered an important component if the genotype is the main driver of the phyllosphere composition. In order to answer this question, we have analysed several factors influencing the structure of the phyllosphere microbial community. Using amplicon sequencing of the 16S rRNA gene and of the internal transcribed spacer (ITS), we explored the microbial diversity at genus level for both bacteria and fungi present in the phyllosphere of leaves and grape berries. We analysed it on different grape taxonomic level (between five Vitis species or a set of Vitis vinifera cultivars chosen to represent the three genetic pools of the species), for different years and on five commercially important varieties of Vitis vinifera that were sampled from three different French terroirs. Our results indicated the presence of complex microbial diversity and assemblages in the phyllosphere. A significant effect of several factors (organ, grape species, growing year and terroir) on taxa abundance was observed with varying degrees of effect. At a given location, genotypes have an impact on microbial assemblage in the phyllosphere of leaf and berries, most pronounced on fruits but the effect of terroir was much stronger than the cultivar identity when the leaf phyllosphere of five grapevine varieties grown in different agro-climatic zones was compared. Limitations of the study as well as implied consequences of this work will be discussed

Agronomic classification between vineyards ('Verdejo') using NDVI and Sentinel-2 and evaluation of their wines

A classification between three vineyards belonging to the Appellation of Origin Rueda (Castilla y León, Spain) has been established in veraison to determine the productive capacities of each vineyard and to study their impact on the grape quality. Several open-access multispectral images obtained from the SENTINEL-2A satellite in the year 2016 were used to calculate the NDVI (Normalized Difference Vegetation Index), which provides information about the vigour of the vineyards. Eleven cloud-free images were assessed and based on the NDVI, three vigour levels were established: high vigour (0.356-0.458), medium vigour (0.285-0.355) and low vigour (0.166-0.284). A level of vigour was assigned to each vineyard according to the NDVI mean values of its pixels. Significant differences were found in the pruning wood weight and yield: high, medium and low vigour values were 2438, 1895 and 1487 kg·ha-1 and 15984, 12990 and 10576 kg·ha-1, respectively. The highest values of total acidity (6.04 g·L-1) and tartaric acid (9.05 g·L-1) have been obtained in low vigour, as well as the lowest values of pH (3.26), malic acid (0.42 g·L-1) and potassium (1640 ppm). Finally, one wine per vigour was produced and a tasting was carried out to check if the differences between the vineyards were perceptible. According to the obtained results, the NDVI is a good indicator to classify vineyards, finding notable differences between the experimental treatments studied

Ultrasonic treatments during the alcoholic fermentation of red wines: effects on 'Syrah' wines

Grapes grown in warm climates have shorter ripening periods. This makes the regular level of several compounds related to sensory properties in wine to remain low. Therefore, those grapes need to receive a particular treatment during winemaking processes if they have to reach the adequate content levels of colour and aroma related compounds. Applying ultrasound during some of the winemaking procedures may contribute to improving the maceration process, which would result in a higher recovery of compounds from grape skins and seeds to the must. This work studies the effect of applying ultrasound to 'Syrah' musts for two different time lengths during its alcoholic fermentation. The wines produced according to regular winemaking procedures (reference wines) were then compared to wines that had been produced under the effect of ultrasound for 30 to 60 min per day. The results showed that the wines produced using ultrasound had concentrations of volatile compounds higher than their reference wine. These data were consistent with the results from the tasting panel, where the judges highlighted the red fruit notes of the wines resulting from the application of ultrasound during the alcoholic fermentation. On the other hand, there were differences between the two wines resulting from applying ultrasound for two different lengths of time, applying ultrasound for 30 min per day proved to be more effective in terms of aroma than applying ultrasounds for 60 min per day. The conclusion of this research is that applying ultrasound during the alcoholic fermentation favours the extraction of volatile compounds. However different times can produce different results. Furthermore, an excessive application of ultrasound may lead to the degradation of some of the compounds of interest