Assessment of changes in Grenache grapevine maturity in a Mediterranean context over the last half-century

This study aims to i) evaluate some descriptive variables for Grenache berry composition over the last 50 years in the southern Rhône Valley wine-growing region and ii) analyse the impacts of climate on the main annual developmental phases of the Grenache berry to understand recent changes observed in the vineyard. A large and spatialised historical, open database from the Rhône Valley grape maturity network (1969–2020) was used to explore trends in grape profile during maturity and at harvest. Then, gridded climate data was used for processing phenological stages and ecoclimatic indicators. Significant changes in grapevine phenology and maturity dynamics were found and linked with changes to ecoclimatic indicators by carrying out a correlation analysis. Depending on the phenological phases, a limited number of ecoclimatic indicators had a significant effect on the maturity profile. The results highlight direct climate impacts on different maturity and yield variables over the last 50 years. These results provide important information about future issues in grape production and the implications for managing viticulture adaptation strategies and thus serve as a basis for assessing, prioritising and optimising technical means of maintaining current grape quality and yield.This study uses an ecoclimatic approach for examining in detail the effects of climate change on the Grenache grape variety in a Mediterranean context. The open database provides the latest information from a large network of plots and over a long period of time, making it possible to validate many results recorded in the literature. This is the first study to use this open database and we wish this database could lead to further explorations and results in viticulture and climate change issues.

Biostimulants in Viticulture: A Sustainable Approach against Biotic and Abiotic Stresses

Climate change and disproportionate anthropogenic interventions, such as the excess of phytopharmaceutical products and continuous soil tillage, are jeopardizing viticulture by subjecting plants to continuous abiotic stress. One of the main physiological repercussions of abiotic stress is represented by the unbalanced redox homeostasis due to the overproduction of reactive oxygen species (ROS), ultimately leading to a state of oxidative stress (detrimental to grape quality). To these are added the direct and indirect damages caused by pathogens (biotic stresses). In light of this scenario, it is inevitable that sustainable techniques and sensitivity approaches for environmental and human health have to be applied in viticulture. Sustainable viticulture can only be made with the aid of sustainable products. Biostimulant (PB) applications (including resistance inducers or elicitors) in the vineyard have become interesting maneuvers for counteracting vine diseases and improving grape quality. These also represent a partial alternative to soil fertilization by improving nutrient absorption and avoiding its leaching into the groundwater. Their role as elicitors has important repercussions in the stimulation of the phenylpropanoid pathway by triggering the activation of several enzymes, such as polyphenol oxidase, lipoxygenase, phenylalanine ammonia-lyase, and peroxidase (with the accumulation of phenolic compounds). The present review paper summarizes the PBs’ implications in viticulture, gathering historical, functional, and applicative information. This work aims to highlight the innumerable beneficial effects on vines brought by these products. It also serves to spur the scientific community to a greater contribution in investigating the response mechanisms of the plant to positive inductions.

Volatile Metabolism of Wine Grape Trincadeira: Impact of Infection with Botrytis cinerea

The aroma of grapes is cultivar dependent and is influenced by terroir, vineyard practices, and abiotic and biotic stresses. Trincadeira is a non-aromatic variety associated with low phenolic content and high sugar and organic acid levels. This cultivar, widely used in Portuguese wines, presents high susceptibility to Botrytis cinerea. This work aimed to characterise the volatile profile of Trincadeira grapes and how it changes under infection with B. cinerea. Thirty-six volatile organic compounds were identified, from different functional groups, namely alcohols, ester acetates, fatty acid esters, fatty acids, aldehydes, and products of the lipoxygenase pathway. Both free and glycosidic volatile organic compounds were analysed by Gas Chromatography and Gas Chromatography coupled to Mass Spectrometry for component quantification and identification, respectively. A multivariance analysis showed a clear discrimination between healthy and infected grapes with 2-trans-hexenal and isoamyl-acetate among the compounds identified as negative and positive markers of infection, respectively. Ester acetates such as 2-phenylethyl acetate, isoamyl acetate, and 2-methylbutyl acetate were present in higher contents in infected samples, whereas the contents of several fatty acid esters, such as ethyl decanoate and ethyl dodecanoate, decreased. These data were integrated with quantitative PCR data regarding genes involved in volatile metabolism and showed up-regulation of a gene coding for Hydroperoxide Lyase 2 in infected grapes. Altogether, these changes in volatile metabolism indicate an impact on the grape quality and may be related to defence against B. cinerea. The presence/absence of specific compounds might be used as infection biomarkers in the assessment of Trincadeira grapes’ quality.

Secondary Metabolites Coordinately Protect Grapes from Excessive Light and Sunburn Damage during Development

Sunburn is a physiological disorder that reduces grape quality and vineyard yield. It is the result of excessive sunlight and high temperatures. As climate change continues to increase air temperatures, reports of sunburn damage in vineyards worldwide are becoming more frequent. Grapes produce secondary metabolites (carotenoids, polyphenols and aroma compounds) to counter photooxidative stress and acclimate to higher radiation environments. This study evaluated changes in these compounds in during ripening when grapes were exposed post-flowering (ED) and at véraison (LD), and compared them to a nondefoliated control (ND). ND contained more α-terpineol and violaxanthin, and the defoliated treatments contained more zeaxanthin, β-carotene, C6 compounds and flavonoids. ED berries adapted better to higher-light environments, displayed larger changes in secondary metabolite concentrations and lower levels of sunburn damage than LD berries did. The composition of berries with increasing sunburn damage was evaluated for the first time. Berries with no damage had the lowest concentrations of flavonoids and oxidized glutathione, and the highest concentrations of chlorophyll and α-terpineol. As damage increased, destruction of photosynthetic pigments, increase in polyphenols and loss of aroma compounds were evidenced. A significant effect of temperature and developmental stage on grape composition was also observed. This study provides a holistic overview of changes in secondary metabolites experienced by grape berries when exposed to excessive light, how these vary along development and how they affect sunburn incidence.

Influence of crop load on the yield and grape quality of Merlot and Vranac (Vitis vinifera L.) varieties in Trebinje vineyard

<p class="042abstractstekst">The aim of this study was to study the impact of crop load on the yield and grape quality of ‘Merlot’ and ‘Vranac’ (<em>Vitis vinifera</em> L.) in Trebinje vineyard. The crop load levels studied in this trial were 9 buds (V1) and 12 buds (V2) per vine at each variety trained on Lenz-Moser bilateral cordon system. The impact was determined by measurements of yield per vine and grape quality characterized by the contents of total soluble solids, titratable acidity, total phenolics, total flavonoids and by total antioxidant capacity. The measured parameters of grape quality of ‘Merlot’ and ‘Vranac’ were not influenced significantly by crop load levels. V2, compared to the V1, showed the potential for increasing grape yield only for Merlot variety under experimental conditions. The results of this study also showed a positive correlation between total phenolics/flavonoids and total antioxidant capacity of grape berries in both varieties, regardless of crop loads applied.</p>

A systematic review and meta-analysis of vineyard techniques used to delay ripening.

Several vineyard techniques have been proposed to delay grape maturity in light of the advanced maturation driven by increasingly frequent water and heat stress events that are detrimental to grape quality. These studies differ in terms of their experimental conditions, and in the present work we have attempted to summarize previous observations in a quantitative, data-driven systematic review. A meta-analysis of quantitative data gathered across 43 relevant studies revealed the overall significance of the proposed treatments and evaluated the impact of different experimental conditions on the outcome of antitranspirants, delayed pruning and late source limitation. Antitranspirants were most effective when applied twice and closer to veraison, while di-1-p-menthene increased the ripening delay by about 1°Brix compared to kaolin. Larger ripening delays were achieved with delayed pruning of low-yielding vines or by pruning at later stages of apical bud development. Late defoliation or shoot trimming delayed ripening in high-yielding vines and represent suitable solutions for late-harvested varieties, but became ineffective where the treatment decreased yield. This quantitative meta-analysis of 242 primary observations uncovers factors affecting the efficacy of vineyard practices to delay ripening, which should be carefully considered by grape growers attempting to achieve this outcome.

Automated Vigor Estimation on Vineyards

Estimating the balance or vigor in vines, as the yield to pruning weight relation, is a useful parameter that growers use to better prepare for the harvest season and to establish precision agriculture management of the vineyard, achieving specific site planification like pruning, debriefing or budding. Traditionally growers obtain this parameter by first manually weighting the pruned canes during the vineyard dormant season (no leaves); second during the harvest collect the weight of the fruit for the vines evaluated in the first step and then correlate the two measures. Since this is a very manual and time-consuming task, growers usually obtain this number by just taking a couple of samples and extrapolating this value to the entire vineyard, losing all the variability present in theirs fields, which imply loss in information that can lead to specific site management and consequently grape quality and quantity improvement. In this paper we develop a computer vision-based algorithm that is robust to differences in trellis system, varieties and light conditions; to automatically estimate the pruning weight and consequently the variability of vigor inside the lot. The results will be used to improve the way local growers plan the annual winter pruning, advancing in the transformation to precision agriculture. Our proposed solution doesn\textsc{\char13}t require to weight the shoots (also called canes), creating prescription maps (detail instructions for pruning, harvest and other management decisions specific for the location) based in the estimated vigor automatically. Our solution uses Deep Learning (DL) techniques to get the segmentation of the vine trees directly from the image captured on the field during dormant season

Tuning Potassium Fertilization to Improve pH and Acidity in Glera Grapevine (Vitis vinifera L.) under a Warming Climate

Potassium concentration in grape berries can affect acidity and pH in must and wines. Under the current warming scenario, where preserving equilibrated value for these grape parameters is increasingly challenging, K fertilization could represent a tool to manage grape composition. In this study, the effect of potassium fertilization was investigated over 4 years (2013–2016) in field-grown grapevines (Vitis vinifera cv. Glera). Four different potassium rates (0, 15, 30, 60 kg K2O ha−1 year−1) were tested and agronomic responses, grape quality as well as K concentration in the berry were recorded over the four years. At harvest, yield parameters and total soluble solids were unaffected by potassium fertilization. On the contrary, the titratable acidity of the musts was increased by the higher rate of potassium (K60), and both tartaric and malic acids showed higher values when the K rate was higher. K fertilization did not affect the pH, as all the treatments displayed comparable pH values and in an optimal range for winemaking. Overall, in our experimental conditions, medium potassium inputs showed better results on Glera grape quality compared to low K rates, by promoting higher titratable acidity levels without altering the pH in musts.