Sugar levels in grape berries are necessary for wine production but also, they are the main driver of most ripening processes. Sugar levels are very responsive to canopy and crop load adjustments. The aim of this study is to test the effect of different levels of defoliation and cluster thinning on grape ripening and wine composition. 'Cabernet sauvignon' grapevines (Vitis vinifera L.) were subjected to defoliation (keeping 100 %, 66 % and 33 % of the leaves) and fruit thinning treatments (keeping 100 %, 66 % and 33 % of the clusters) combined in a factorial design. The experiment was repeated for 2 consecutive seasons (2017 and 2018) and the plants were left untreated for a third season (2019) to observe the carry-over effects of the treatments. The treatments implied precise adjustments of leaf and cluster numbers. However, the proportion of leaf area to fruit mass tended to compensate each other and interact resulting in smaller differences in leaf area or fruit mass by harvest. Berry mass was strongly reduced by defoliation even in the subsequent season where no defoliation was applied. Berry ripening indicators (soluble solids, acidity and anthocyanin levels) were also more affected by defoliation than fruit thinning. Anthocyanin profile was shifted to a higher proportion of Malvidin-derived anthocyanins for defoliated vines and lower proportion of Malvidin-derived anthocyanins in the case of thinned vines. However, when it came down to wine, the physicochemical parameters as well as the aroma profile were more affected by cluster thinning. There was a clear relationship between sugar levels of the unfermented must and many winearoma compounds. Green aromas (2-isobutyl-3-methoxypyrazine, hexanol and cis-3-Hexen-1-ol) were among those presenting a negative correlation to must sugar whereas other compounds like Isobutyric acid, Benzyl alcohol, 1-Octen-3-ol and gamma-Nonalactone had a positive correlation. This study reveals a higher level of complexity of source sink relations where leaves and clusters do not only act as a source and a sink of carbon, respectively. Therefore, the results of this study should be considered before making comparisons of leaf area to fruit mass ratios across different vine-growing systems.

Grapevine red blotch virus (GRBV) negatively affects the composition of grapevine (Vitis vinifera L.) berries by reducing total soluble solids and anthocyanins, leading to economic losses for grape producers. Negative effects of GRBV were suspected to be due to impeded carbon translocation from leaves to fruit which limits sugar and flavonoid accumulation in berries. A two-year trial was conducted to determine whether an increase in source: sink ratio may affect sugar allocation and mitigate the effects of GRBV on Cabernet-Sauvignon plants. Experimental design was factorial (2 by 2) with healthy plants that did not have the virus (GRBV (-)) and plants having GRBV (GRBV (+)) and plants were subjected either untreated (UNT) or cluster thinned down to 10 clusters (CT). Effects of cluster thinning and virus status on leaf and shoot total soluble sugars (TSS), plant water status, leaf gas exchange, berry primary and secondary metabolites, and yield components were measured. The TSS in leaves began to accumulate around veraison. In shoot sap, GRBV(-) plants had greater concentration in TSS than GRBV(+) plants. The presence of disease improved plant water status increasing the stem water potential and increasing berry mass. However, juice total soluble solids were consistently lower in GRBV(+) plants despite increasing source: sink ratio by 3x with cluster removal. Likewise, GRBV(+) plants produced berries with lower anthocyanin content at harvest regardless of CT in both years. Our results suggest that GRBV infection severally impeded carbohydrate translocation out of the leaves, and in contrast to healthy plants reducing the number of clusters does not induce a reconcentration of sugars in the remaining clusters.

Background and Aims: Atmospheric carbon dioxide (CO2) levels and temperature are expected to increase in the next decades. In addition, changes in climate as well as the stratospheric ozone concentration may affect the exposure of viticultural regions to UV-B. The aim of the present study was to investigate the effect of combined elevated CO2 and increased temperature (+CO2/+T) regimes and UV-B radiation on anthocyanin and flavonol biosynthesis in grape berries. Methods and Results: Three UV-B doses [0, 5.98 and 9.66kJ/(m(2)d)] and two CO2-day/night temperature regimes (390 mol/mol CO2-24/14 degrees C and 700mol/mol CO2-28/18 degrees C) were imposed on Vitis vinifera cv. Tempranillo fruit-bearing cuttings from fruitset to maturity. Berry mass, composition and expression of selected genes were monitored. The time to reach veraison and maturity was reduced under +CO2/+T. Anthocyanin concentration under +CO2/+T was higher 2 weeks after veraison, but lower at maturity. Ultraviolet-B radiation slowed berry development and upregulated flavonol and anthocyanin biosynthesis. Conclusions:The effect of UV-B, which modulates the accumulation of sugars and upregulates anthocyanin biosynthesis, compensated the deleterious effect of elevated CO2 and increased temperature on berry anthocyanin concentration. Significance of the Study: Certain viticultural practices, such as leaf removal, that modify the exposure of grapes to UV-B and the leaf surface to fruit mass ratio, may alleviate ...

This work aims to characterize the physiological response of grapevine (Vitis vinifera L.) cv. Tempranilloto UV-B radiation under water deficit conditions. Grapevine fruit-bearing cuttings were exposed tothree levels of supplemental biologically effective UV-B radiation (0, 5.98 and 9.66 kJ m¿2day¿1) andtwo water regimes (well watered and water deficit), in a factorial design, from fruit-set to maturityunder glasshouse-controlled conditions. UV-B induced a transient decrease in net photosynthesis (Anet),actual and maximum potential efficiency of photosystem II, particularly on well watered plants. Methanolextractable UV-B absorbing compounds (MEUVAC) concentration and superoxide dismutase activityincreased with UV-B. Water deficit effected decrease in Anetand stomatal conductance, and did notchange non-photochemical quenching and the de-epoxidation state of xanthophylls, dark respirationand photorespiration being alternative ways to dissipate the excess of energy. Little interactive effectsbetween UV-B and drought were detected on photosynthesis performance, where the impact of UV-Bwas overshadowed by the effects of water deficit. Grape berry ripening was strongly delayed when UV-Band water deficit were applied in combination. In summary, deficit irrigation did not modify the adaptiveresponse of grapevine to UV-B, through the accumulation of MEUVAC. However, combined treatmentscaused additive effects on berry ripening.

The increase in grape berry ripening rates associated to climate change is a growing concern for wine makers as it rises the alcohol content of the wine. The present work studied the combined effects of elevated CO2, temperature and UV-B radiation on leaf physiology and berry ripening rates. Three doses of UV-B: 0, 5.98, 9.66 kJ m(-2) d(-1), and two CO2-temperature regimes: ambient CO2-24/14 degrees C (day/night) (current situation) and 700 ppm CO2-28/18 degrees C (climate change) were imposed to grapevine fruit-bearing cuttings from fruit set to maturity under greenhouse-controlled conditions. Photosynthetic performance was always higher under climate change conditions. High levels of UV-B radiation down regulated carbon fixation rates. A transient recovery took place at veraison, through the accumulation of flavonols and the increase of antioxidant enzyme activities. Interacting effects between UV-B and CO2-temperature regimes were observed for the lipid peroxidation, which suggests that UV-B may contribute to palliate the signs of oxidative damage induced under elevated CO2-temperature. Photosynthetic and ripening rates were correlated. Thereby, the hastening effect of climate change conditions on ripening, associated to higher rates of carbon fixation, was attenuated by UV-B radiation.

UV-B radiation and water deficit may trigger flavonol and anthocyanin biosynthesis in plant tissues. In addition, previous research has showed strong qualitative effects on grape berry skin flavonol and anthocyanin profiles in response to UV-B and water deficit. The aim of this study is to identify the mechanisms leading to quantitative and qualitative changes in flavonol and anthocyanin profiles, in response to separate and combined UV-B and water deficit. Grapevines (Vitis vinifera L. cv. Tempranillo) were exposed to three levels of UV-B radiation (0, 5.98 and 9.66 kJm(-2) day(-1)) and subjected to two water regimes. A strong effect of UV-B on flavonol and anthocyanin biosynthesis was found, resulting in an increased anthocyanin concentration and a change in their profile. Concomitantly, two key biosynthetic genes (FLS1 and UFGT) were up-regulated by UV-B, leading to increased flavonol and anthocyanin skin concentration. Changes in flavonol and anthocyanin composition were explained to a large extend by transcript levels of F3'H, F3'5'H and OMT2. A significant interaction between UV-B and water deficit was found in the relative abundance of 3'4' and 3'4'5' substituted flavonols, but not in their anthocyanin homologues. The ratio between 3'4'5' and 3040 substituted flavonols was linearly related to the ratios of F3'5'H and FLS1 transcription, two steps up-regulated independently by water deficit and UV-B radiation, respectively. Our results indicate that changes in flavonol profiles in response to environmental conditions are not only a consequence of changes in the expression of flavonoid hydroxylases; but also the result of the competition of FLS, F3'5'H and F3'H enzymes for the same flavonol substrates.

Grapevine cv. Tempranillo fruit-bearing cuttings were exposed to supplemental ultraviolet-B (UV-B) radiation under controlled conditions, in order to study its effect on grape traits, ripening, amino acids and flavonoid profile. The plants were exposed to two doses of UV-B biologically effective (5.98 and 9.66kJm(-2)d(-1)), applied either from fruit set to ripeness or from the onset of veraison to ripeness. A 0kJm(-2)d(-1) treatment was included as a control. UV-B did not significantly modify grape berry size, but increased the relative mass of berry skin. Time to reach ripeness was not affected by UV-B, which may explain the lack of changes in technological maturity. The concentration of must extractable anthocyanins, colour density and skin flavonols were enhanced by UV-B, especially in plants exposed from fruit set. The quantitative and qualitative profile of grape skin flavonols were modified by UV-B radiation. Monosubstituted flavonols relative abundance increased proportionally to the accumulated UV-B doses. Furthermore, trisubstituted forms, which where predominant in non-exposed berries, were less abundant as UV-B exposure increased. Although total free amino acid content remained unaffected by the treatments, the increased levels of gamma-aminobutyric acid (GABA), as well as the decrease in threonine, isoleucine, methionine, serine and glycine, revealed a potential influence of UV-B on the GABA-mediated signalling and amino acid metabolism. UV-B had an overall positive impact on grape berry composition.

The present study aimed at evaluating the short- and long-term effects of UV-B radiation on leaves of grapevine Vitis vinifera (cv. Tempranillo). Grapevine fruit-bearing cuttings were exposed to two doses of supplemental biologically effective UV-B radiation (UV-BBE) under glasshouse-controlled conditions: 5.98 and 9.66 kJ m(-2) d(-1). The treatments were applied either for 20 d (from mid-veraison to ripeness) or 75 d (from fruit set to ripeness). A 0 kJ m(-2) d(-1) UV-B treatment was included as control. The main effects of UV-B were observed after the short-term exposure (20 d) to 9.66 kJ m(-2) d(-1). Significant decreases in net photosynthesis, stomatal conductance, sub-stomatal CO2 concentration, the actual photosystem II (PSII) efficiency, total soluble proteins and de-epoxidation state of the VAZ cycle were observed, whereas the activities of several antioxidant enzymes increased significantly. UV-B did not markedly affect dark respiration, photorespiration, the maximum potential PSII efficiency (Fv/Fm), non-photochemical quenching (NPQ), as well as the intrinsic PSI! efficiency. However, after 75 d of exposure to 5.98 and 9.66 kJ m(-2) d(-1) UV-B most photosynthetic and biochemical variables were unaffected and there were no sign of oxidative damage in leaves. The results suggest a high long-term acclimation capacity of grapevine to high UV-B levels, associated with a high accumulation of UV-B absorbing compounds in leaves, whereas plants seemed to be tolerant to moderate doses of UV-B.

La vid (Vitis vinifera L.) se maneja para equilibrar la relación entre el área foliar (fuente) y lamasa de frutos (sumidero). El objetivo de este trabajo fue estudiar los efectos acumulativos de lamanipulación del equilibrio entre fuentes y sumideros en la fisiología de la vid. Plantas de`Cabernet Sauvignon' fueron sometidas a tratamientos de defoliación (33, 66 y 100% de lashojas retenidas) y aclareo de racimos (33, 66 y 100% de los racimos retenidos) siguiendo undiseño factorial. En la primera campaña, el aclareo apenas estuvo relacionado con los sólidossolubles de la baya, mientras que en la segunda campaña estuvieron fuertementecorrelacionados, lo que sugiere un posible efecto de aclimatación. Los tratamientos dedefoliación tuvieron un gran impacto en el tamaño de las bayas, en el número de las bayas porracimo, sólidos solubles y el intercambio de gases de las hojas en ambos años. El efectopredominante de la defoliación se reflejó en la reducción del contenido de almidón de la raíz, subiomasa, y un retraso del envero y en la senescencia de la hoja, así como de la cosecha, que seretrasó hasta 9 semanas en el tratamiento en el que se mantuvieron el 33% de las hojas. Losniveles de antocianinas de las bayas se redujeron cuando la maduración se vio afectada. Sinembargo, los niveles de antocianinas se recuperaron en los tratamientos defoliados cuando estosalcanzaron la madurez. En una tercera campaña, en la que no se aplicaron los tratamientos, lascepas que habían sido sometidas a defoliación en temporadas anteriores tuvieron efectos claros.Equilibrar la relación fuente-sumidero es crucial para obtener una adecuada velocidad demaduración. Sin embargo, la regulación fuente-sumidero es más compleja y el efecto defoliaciónsuperó la contraprestación del aclareo de racimos.