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Delaying the date of the first hedge-trimming (or ‘tip-pruning’) is of limited technical value in vineyard canopy management. The impact of the delay on lateral shoot growth and must composition remains marginal within the context of the La Côte vineyard in Switzerland.

Over the course of a six-year trial, we investigated the physiological response of the Swiss white cultivar Vitis vinifera Petite Arvine, rich in varietal thiols, to the following canopy removal treatments from the cluster area, i.e. from the shoot base to the sixth leaf of each shoot: A) lateral shoots only, B) lateral shoots + 50 % main leaves, C) lateral shoots + 100 % main leaves or D) main leaves only. All leaf removal (LR) treatments were performed at the pre-flowering stage. Intensive pre-flowering removal of both lateral shoots + 100 % main leaves from the cluster area (C) strongly reduced yield potential (‒47 % on average) and tended to reduce the concentration of 3-mercaptohexanol precursors (Cys-3MH) in the must (‒21 %; p-value < 0.10). The effect of LR on berry set and must composition was modulated by removing fewer main leaves (‒24 % in yield potential and ‒6 % in Cys-3MH concentration). Climate conditions primarily influenced yield and grape composition. Main leaves and lateral shoots played different physiological roles: removal of main leaves only (D) resulted in a larger leaf area (+15 %) due to the development of lateral shoots in the cluster area and a lower yield potential (‒12 %) due to fewer berries per cluster when compared one-to-one with removal of lateral shoots only (A). In the must at harvest, treatment D had higher concentrations of malic acid (+12 %), yeast-assimilable nitrogen (+10 %) and glutathione (+8 %), but there were no significant trends for TSS, pH, Cys-3MH or Folin index. The overall effects of pre-flowering LR on wine composition were negligible in the context of this trial. The study highlighted the different physiological roles of the main leaves and lateral shoots, suggesting that pre-flowering leaf removal should be used cautiously, taking into account the plant’s resilience to environmental conditions. This research is part of a broader project on grapevine canopy management in temperate climates in Switzerland.

The effectiveness of an application of foliar nitrogen at veraison depends on the initial level of vine nitrogen deficiency, an Agroscope study has shown. The threshold levels of assimilable nitrogen deficiency in the grape must are validated for Chardonnay but still need to be confirmed for Sauvignon Blanc.

Grapevine leaf removal (LR) in the cluster area is a common practice in temperate and cool climates, usually done between berry-set and cluster closure to create a less favourable microclimate for fungal diseases and to improve grape ripening. When applied before flowering, LR affects berry-set and is, therefore, an effective yield-control tool, reducing time-consuming manual cluster thinning; it also improves berry structure and composition (i.e., total soluble sugars [TSS], titratable acidity [TA] and polyphenols) (VanderWeide et al., 2021). The present five-year trial follows a previous study about pre-flowering LR under identical environmental conditions (Verdenal et al., 2019); it validates the sustainability of moderate pre-flowering LR and its possible mechanisation under Swiss climatic conditions, using low-pressure double airflow.

Knowledge of the nitrogen nutrition status of the vine is essential for long-term management of its nutrition with the aim of producing high-quality grapes. Measurement of the chlorophyll index is a fast, non-destructive and relatively inexpensive method that provides a good approximation of the nitrogen nutrition status of the vine during the growing season. Several chlorophyll meters are available on the market, each using its own measurement unit. With the aim of popularizing the use of chlorophyll meters, the interpretation thresholds of the SPAD index, measured on the vine at the veraison stage, have been established from correlation with the N-tester index, for which the thresholds are already known.

The present trial follows a previous study about pre-flowering leaf removal (LR) (Verdenal et al., 2019) and validates the sustainability of mechanical pre-flowering LR under local Swiss vineyard conditions, using a low-pressure double airflow, to reduce the cost of laborious bunch thinning. In previous studies, pre-flowering LR has shown additional benefits over post-berry-set LR in terms of yield regulation and grape and wine compositions. This trial had two objectives: 1) to test the technical feasibility of mechanical pre-flowering LR, using a low-pressure double airflow and 2) to observe the impact of this practice over five years on yield parameters, grape composition at harvest and wine quality over five years. For this purpose, a trial was conducted on the two cultivars, Doral (white) and Gamay (red), to compare four LR treatments, that is, A) mechanical post-berry-set LR, B) manual pre-flowering LR, C) mechanical pre-flowering LR, and D) double mechanical pre-flowering + post-berry-set LR. More broadly, this work provides practical insights into the consequences of pre-flowering LR on the grapevine, pointing out the advantages and the limits of intensity, timing and mechanisation of this practice. In comparison with the mechanical post-berry-set LR, mechanical pre-flowering LR induced a 7 % loss in bud fruitfulness, a 30 % yield loss and a 3 % gain in total soluble solids (TSS) accumulation in grapes in both cultivars, although the improvement in grape maturity was small and uneven through the years; Gamay anthocyanin concentration remained stable. Pre-flowering LR had no overall impact on the quality of Doral and Gamay wines. Damage was observed on the inflorescences due to the intensity of mechanical pre-flowering LR, which resulted in fewer berries per cluster and a lower yield than with manual LR by the same date. A second LR after berry set was also tested to limit the growth of laterals and clean the clusters from the remaining flower caps to prevent the development of fungal diseases, but it did not show any benefit over a single pre-flowering LR. In conclusion of this trial, a single, moderate mechanical pre-flowering LR is an effective and sustainable practice under temperate climatic conditions, to reduce the costs of laborious manual pre-flowering LR.

Nitrogen (N) is an essential element for vine development and yield; it is also involved in the winemaking process and significantly affects wine composition. It is therefore essential to control and optimise plant N use to ensure an adequate N composition of the grapes at harvest. An improved understanding of the impact of cultivation practices on plant N metabolism would allow a better orientation of technical choices with the objective of quality and sustainability (i.e., fewer inputs, more efficiency). Our trial focused on the impacts of fertilisation and crop thinning on grape N composition. A wide crop load gradient was set up in a homogeneous plot of Chasselas (Vitis vinifera L.) in an experimental vineyard in Switzerland. Foliar urea was applied at veraison in order to compare it with an unfertilised control. Vine development and grape composition were evaluated over two years, with particular attention to the carryover effects of both fertilisation and crop thinning. Foliar N fertilisation effectively increased the amount of N in grapes at harvest in the same year, but had no impact on grape ripeness or carryover effect on year n + 1. Conversely, crop thinning improved grape maturity by reducing fruit N and C demand. Interestingly, amino N proportions could be distinguished according to crop load, while the global grape N concentration at harvest remained unchanged. Some amino acids were more affected by crop thinning than others. The concentrations of alanine, γ-aminobutyric acid (GABA), serine and threonine were reduced by crop thinning. Crop thinning had a strong carryover effect on year n + 1. The carryover impact of crop thinning on grapes in terms of both maturation index and N composition could be observed at the onset of grape ripening on year n + 1. This experiment highlighted the influence of the previous year’s agricultural practices on grape C and N accumulation before and during the ripening phase. Consequently, the modulation of grape composition at harvest should be considered over two consecutive years. These results will contribute to the improvement of predictive models and sustainable agronomic practices in perennial crops.

Under the global warming scenario, water scarcity is expected to intensify in most grape-growing regions. The use of drought-tolerant rootstocks is considered a useful tool to mitigate the negative effects of soil water deficit on vine functioning. Differences in leaf gas exchange, plant water status, specific hydraulic conductivity in petioles (Kpetiole), xylem vessel size and vegetative vigour of field-grown Pinot noir grafted onto five rootstocks (3309C, 101-14 MGt, Kober 5BB, Riparia Gloire de Montpellier, 41B MGt) were investigated during one season under water deficit in Switzerland. The water deficit was imposed by installing waterproof and non-reflecting plastic sheets on the soil from March to harvest (September) to avoid rainfall infiltration. Rootstocks had stronger effects on vine water status than on gas exchanges. During the grape ripening stage, vines grafted onto 41B MGt and 101-14 MGt were characterised by more severe water stress as shown by the lowest values of pre-dawn leaf (Ψpd), stem water potential (Ψstem) and water stress integral (SΨ), whereas 3309C and Kober 5BB rootstocks induced milder effects. Significant differences in photosynthesis (A), stomatal conductance (gs) and transpiration (E) were only observed between vines grafted onto 41B MGt and 3309C at later stages of ripening. Changes induced by rootstocks in shoot vigour, Kpetiole and the number and size of xylem vessels in petioles and stems were correlated to differential responses of Pinot noir to water deficit. The increased vegetative vigour induced by 3309C and Kober 5BB was associated with the highest Kpetiole, xylem vessel size and a good plant water status of Pinot noir under low soil water availability. Kober 5BB induced the highest yield, probably due to the better vine water status, whereas vines grafted onto 41B MGt showed the lowest malic acid content and yeast assimilable nitrogen in berries.

La teneur en azote du moût à la vendange joue un rôle déterminant dans la cinétique de fermentation alcoolique et dans la formation des arômes du vin, particulièrement dans le cas des vins blancs. Au cours des dernières décennies, les pratiques viticoles ont considérablement évolué vers moins d’herbicides et davantage d’enherbement. Dans ce contexte, des carences azotées du moût sont apparues de façon récurrente dans certains vignobles. Comment pouvons-nous adapter nos pratiques culturales à ce contexte de concurrence pour l’azote ?

This review addresses the role of nitrogen (N) in vine balance and grape composition. It offers an integrative approach to managing grapevine N nutrition. Keeping in mind that N excess is just as detrimental to wine quality as N depletion, the control of grapevine N status, and ultimately must N composition, is critical for high-quality grape production. N fertilisation has been intensively used in the past century, despite plants absorbing only 30 to 40 % of applied N. By adapting plant material, soil management and vine balance to environmental conditions, it would be possible for grape growers to improve plant N use efficiency and minimise N input in the vineyard. Vineyard N management is a complex exercise involving a search for a balance between controlling vigour, optimising grape composition, regulating production costs and limiting pollution. The first part of this review describes grapevine N metabolism from root N uptake to vine development and grape ripening, including the formation of grape aroma compounds. The advantages and limits of methods available for measuring plant N status are addressed. The second part focuses on the parameters that influence grapevine N metabolism, distinguishing the impacts of environmental factors from those of vineyard management practices. Areas for further research are also identified.

Aims: The aim of the present study was to analyse the impact of different water regimes on the physiological and agronomical behavior of an aromatic white grapevine (cv. Arvine) by means of various levels of irrigation. The consequences of the plant water status were evaluated by carrying out a chemical (aromatic precursors) and sensorial analysis of the resulting wines. Methods and results: Adult vines of Vitis vinifera L. cv. Arvine grafted onto 5BB were subjected to different water regimes (various levels of irrigation) during the growing season. Physiological indicators were used to monitor the plant water status [pre-dawn leaf (ΨPD) and stem (ΨSTEM) water potentials and carbon isotope composition (d13C) in the must]. Gas exchange (net photosynthesis AN and transpiration E), stomatal conductance (gs), yield parameters, berry composition at harvest, analysis of potential grape aromatic properties (glycosyl-glucose G-G, precursor 3-mercaptohexanol P 3-MH) and the sensorial quality of wines were analysed over a period of 8 consecutive years (2009-2016) in the Agroscope experimental vineyard in Leytron under the relatively dry conditions of the Rhône valley in Wallis, Switzerland. In the non-irrigated vines, the progressively increasing water deficit observed over the season reduced the leaf gas exchange (AN and E) and gs. The intrinsic water use efficiency (WUEi, A/gs) increased over the season and was greater in the vines that had suffered water restriction than in the irrigated vines. The rise in WUEi was correlated with an increase in d13C in the must sugars at harvest. A decrease in plant vigor was observed in the water stressed vines over multiple years. Moderate to high water stress during fruit ripening lowered the contents of total and malic acidity in the musts and the content of yeast available nitrogen (YAN). On the other hand, contents in sugar and the aromatic precursor (P-3MH) in berries were not influenced by the vine water status. The G-G values for berries increased with rising water stress in the non-irrigated vines. The wines from the plants subjected to water stress and to yeast available nitrogen deficiency (non-irrigated vines during hot and dry seasons) had a less distinctive typicity, and developed a lower aromatic expression with a more bitter taste, than the wines from the non-stressed plants. Overall, and compared with the stressed vines, the organoleptic characteristics and quality of Arvine wines from vines which had not undergone restrictions in water and nitrogen during the growing season were appreciated more. Conclusions: The vine’s physiological behavior (leaf gas exchange, plant vigor) and agronomic parameters (yield, berry composition), together with the quality of white aromatic Arvine wines, were strongly influenced by vine water regimes during the growing season. Significance and impact of the study: Vine water status and must nitrogen contents are key factors in grape composition and in the sensorial quality of resulting aromatic white wines.

Defoliation of the vines consists of eliminating the leaves in the grape bunch zone in a more or less intensive manner. It is a long-proven prophylactic technique that has seen a renewed interest in the current context of the reduction of phytosanitary inputs. However, several questions remain. Which is the optimal period? What is the ideal intensity? What are the risks? Is the mechanization of this process a feasible option? Agroscope has been undertaking defoliation trials in Switzerland since 2010 in order to shed light on these questions.

Aims: Agroscope investigated the impact of the leaf-to-fruit ratio on nitrogen (N) partitioning in grapevine following a foliar urea application with the aim of increasing the yeast assimilable nitrogen (YAN) concentration in the must. Methods and results: Foliar urea was applied to field-grown Vitis vinifera L. cv. Chasselas grapevines as part of a split-plot trial with two variable parameters: canopy height (90 or 150 cm) and fruit load (5 or 10 clusters per vine). Foliar application of 20 kg/ha of 15N-labelled urea (10 atom% 15N) was performed at veraison. The isotope labelling method allowed to observe foliar-N partitioning in the plant at harvest. The leaf-to-fruit ratio varied between 0.4 and 1.6 m2/kg, and strongly impacted the N partitioning in the grapevines. Total N and foliar-N partitioning was mainly affected by the variation of canopy height. The YAN concentration varied from 143 to 230 mg/L (+60 %) depending on the leaf area. An oversized canopy (+31 %DW) induced a decrease in the total N concentration of all organs (-17 %), and a decrease in YAN quantity in the must in particular (-53 %). A negative correlation between the N concentration and the carbon isotope discrimination (CID) could be pointed out in a condition of no water restriction (e.g., R2 = 0.65 in the must). Conclusion: An excessive leaf area can induce YAN deficiency in the must. Thus, a balanced leaf-to-fruit ratio – between 1 and 1.2 m2/kg – should be maintained to guarantee grape maturity, YAN accumulation in the must and N recovery in the reserve organs. Significance and impact of the study: The results of this study encourage further research to understand the role of other physiological parameters that affect N partitioning in the grapevine – YAN accumulation in the must in particular – and add new perspectives for N management practices in the vineyard.

Aims: The aim of this research was to study the physiological and agronomical behaviors (leaf gas exchange, plant vigor, mineral supply, and yield components) of the Chasselas grapevine subjected to different water regimes during the growing season. The resulting grape and wine qualities were also determined. Methods and results: Adult vines of Vitis vinifera L. cv. Chasselas (clone 14/33-4, grafted onto 5BB) were subjected to different water regimes (various levels of irrigation) during the growing season. Physiological indicators were used to monitor the plant water status [the predawn leaf (. Leaf photosynthesis (A) and transpiration (E), stomatal conductance (gs), vulnerability to cavitation, yield parameters, berry composition at harvest, and organoleptic quality of wines were analyzed over a period of eight consecutive years between 2009 and 2016, under the relatively dry conditions of the Canton of Wallis, Switzerland. In non-irrigated vines, the progressively increasing water deficit observed over the season reduced the leaf gas exchange (A and E) and gs. The intrinsic water use efficiency (WUEi, A/gs) increased over the season and was greater in vines that had suffered water restriction than in irrigated vines. The rise in WUEi was correlated with an increase in d13C in the must sugars at harvest. Vulnerability to cavitation (embolism phenomenon) increased with increasing water deficit in the non-irrigated vines with covered soils. A decrease in plant vigor was observed in the vines that had been subjected to water restrictions over multiple years. Moderate water stress during fruit ripening was favorable for sugar accumulation in berries and lowered the contents of total and malic acidity in the musts and the content of available nitrogen (YAN). Overall, the organoleptic characteristics and quality of Chasselas wines were little influenced by the vine water regimes, with the exception of the hot, dry season in 2009 (and, to a lesser degree, in 2011). In those years, the quality of the wines from the irrigated vines, which had not suffered any water stress, received a better appreciation. Bitterness was generally greater in samples from the non-irrigated vineyards that had suffered from drought than in samples from the irrigated vines. No significant differences in the aroma and wine structure were measured during the study period, regardless of the vine irrigation status. Conclusions: The physiological behavior (gas exchange, plant vigor, and mineral supplies) and grape ripening in Chasselas vines were largely dependent on the water supply conditions in the vineyard during the growing season. Significance and impact of the study: Vine water status is a key factor in leaf gas exchange, canopy water use efficiency, berry composition and, lastly, wine quality.

Aim: The objective of this work is to investigate the effects of early defoliation on cv. Chasselas under the temperate conditions of Switzerland, with particular attention to berry anatomical traits and wine sensory parameters. Methods and results: Defoliation (removal of 6 basal leaves + 6 lateral shoots per shoot) was completed during three developmental stages of grapevine, i.e., pre-flowering, late flowering and bunch closure, and at two intensity levels. The experimentation was performed repeatedly over four years. In addition to vintage effect, pre-flowering defoliation had a consistent impact on vine agronomic behaviour. The yield was highly affected by the technique (more than 30% loss). Earlier and more intense defoliation had more impact on yield, while post-berry-set defoliation had no effect on yield. Intensive defoliation also modified berry skin thickness and had a positive impact inhibiting Botrytis development. Wine composition and sensory analysis were not affected by the practice. However, pre-floral defoliation affected bud fruitfulness and vigour, i.e., trimming and pruning weights. This result noted a carryover effect that could affect vine sustainability under restrictive conditions. Conclusion: In the context of this study, pre-flowering defoliation seems to be an interesting practice to reduce vigour and control the high production potential of the cv. Chasselas. The intensity of early defoliation allows for the modulation of the impact on the yield in order to prevent excessive yield loss. Significance and impact of the study: Pre-flowering defoliation of the white cultivar represents a prophylactic solution to reduce both chemical entrants and bunch-thinning costs.

Aim: The objective of this work is to investigate the effects of defoliation on cv. Pinot noir under the mild-climate conditions of Switzerland, with particular attention to berry anatomical traits and wine sensory parameters. Methods and results: Defoliation (removal of 6 basal leaves + 6 lateral shoots per shoot) was completed at three developmental stages of grapevine, i.e., pre-flowering, late flowering and bunch closure. These experimentations were performed repeatedly over six years. In addition to the vintage effect, pre-flowering defoliation had a consistent impact on vine agronomic behaviour. The yield was highly affected by the technique (-30 %). The berry skin thickness doubled, and the polyphenol concentration increased significantly. The free glutathione concentration in the must decreased. Conclusion: Leaf removal at early pre-flowering stage had tremendous consequences on the vine agronomic performance, mainly to the detriment of berry set, thus having a great impact on yield, berry skin thickness, must composition, and wine composition. Significance and impact of the study: Hypothesis about the competition for assimilates between the growing canopy and the inflorescences during the early season was developed. Furthermore, the role of glutathione and anthocyanins – as antioxidants against UV stress – was interpreted, demonstrating that grapevine is able to adapt to abiotic stresses and ensure a sustainable development.

Aims : The aims of this study were to investigate the physiological behavior (plant hydraulics, gas exchange) of the cultivar Pinot Noir in the field under progressively increasing conditions of water stress and analyze the effects of drought on grape and wine quality. Methods and results : Grapevines of the variety Vitis vinifera L. cv. Pinot Noir (clone 9-18, grafted onto 5BB) were subjected to different water regimes (irrigation treatments) over the growing season. Physiological indicators were used to monitor plant water status (leaf and stem water potentials and relative carbon isotope composition (d13C) in must sugars). Leaf gas exchange (net photosynthesis A and transpiration E), leaf stomatal conductance (gs), specific hydraulic conductivity in petioles (Kpetiole), yield components, berry composition at harvest, and organoleptic quality of wines were analyzed over a 7-year period, between 2009 and 2015, under relatively dry conditions in the canton of Wallis, Switzerland. A progressively increasing water deficit, observed throughout the season, reduced the leaf gas exchange (A and E) and gs in non-irrigated vines. The intrinsic water use efficiency (WUEi, A/gs) increased during the growing season and was greater in water-stressed vines than in well-watered vines (irrigated vines). This rise in WUEi was correlated with an increase in d13C in must sugars at harvest. Drought led to decreases in Kpetiole, E and sap flow in stems. A decrease in vine plant vigor was observed in vines that had been subjected to water deficits year after year. Moderate water stress during ripening favored sugar accumulation in berries and caused a reduction in total acidic and malic contents in must and available nitrogen content (YAN). Wines produced from water-stressed vines had a deeper color and were richer in anthocyanins and phenol compounds compared with wines from well-watered vines with no water stress. The vine water status greatly influenced the organoleptic quality of the resulting wines. Wines made from non-irrigated vines with a water deficit presented more structure and higher-quality tannins. They were also judged to be more full-bodied and with blended tannins than those made from irrigated vines. Conclusions : Grape ripening and resulting Pinot Noir wines were found to be largely dependent on the water supply conditions of the vines during the growing season, which influenced gas exchange and plant hydraulics. Significance and impact of the study : Plant water status constitutes a key factor in leaf gas exchange, canopy water use efficiency, berry composition and wine quality.

Aims: The impact of canopy management on the nitrogen (N) content in grapevines was studied. Methods and Results: Two trials were carried out between 2001 and 2010 on Vitis vinifera cvs. Chasselas and Pinot noir. The observed factors of variation were the intensity of lateral shoot removal for the first trial and the severity of shoot trimming for the second trial. The N content was evaluated in parallel by leaf diagnosis, the chlorophyll index and the yeast available N concentration (YAN) found in the musts. When the yields were the same, a significant dilution of N in proportion to the development of the leaf area was revealed. Treatments resulting in excessive leaf area presented N deficiency in the leaves and the musts. Conclusion: The N content in both the vines and grapes was influenced by the canopy management (lateral shoot removal and shoot trimming), and the magnitude of the response appeared to be even greater in the absence of water stress. In addition, the risk of N deficiency was found to increase beyond a maximum value of the leaf-fruit ratio. Significance of the study: Canopy management has a significant influence on the N content in foliage and grapes, and the risk of N deficiency increases under a situation that produces an excessive leaf area.