Source-Sink manipulations have major implications for grapevine berry and wine flavonoids and aromas that go beyond the changes in berry sugar accumulation

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 wine-aroma 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 γ-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.

Study of the impact of vine cultivation technology on the Feteasca Neagra wine phenolic composition and antioxidant properties

In this work a comparative assessment was performed on individual and total polyphenols and biochemical properties of some Feteasca Neagra red wines obtained from grapes cultivated with different farming technologies (organic vs. conventional). The effect of a 30% cluster thinning treatment in both organic and conventional vineyard, compared to control plots with no thinning, was also monitored. The wines were obtained during two vintages, one with more favourable climatic conditions and one less favourable, in the period 2010-2019. Our results indicate that by applying a 30% cluster thinning treatment in the vineyard it is possible to increase the concentration of total and individual polyphenols of the resulted Feteasca Neagra wines. Furthermore, the differences observed between the phenolic profiles of wines from conventionally and organically produced grapes showed that organic Feteasca Neagra wines have higher phenolic compounds concentrations and antioxidant properties, with some important individual phenols accumulating in larger quantities than in the case of conventional wines. The beneficial effect of the organic cultivation is more evident in years characterised by less favourable climatic conditions. The statistical analysis tools applied to the analytical data allowed a good discrimination of experimental wine variants according to the vine cultivation technology (organic vs. conventional, with and without cluster thinning) and vintage. Thus, the results indicated that the applied cultivation technologies, especially when both organic cultivation and cluster thinning are combined, can greatly improve the polyphenolic content of Feteasca Neagra wines. The absolute value of the increase in polyphenol concentration was higher in favourable years, but the relative increase, in percentages, as compared to control wines, was higher in less favourable years. The combination of both viticultural practices may be thus exploited in order to obtain wines with higher polyphenolic content, which leads to better structure, better ageing potential, enhanced nutritional and antioxidant properties.

Analysis of the phenolic composition and yield of 'BRS Vitoria' seedless table grape under different bunch densities using HPLC-DAD-ESI-MS/MS

Grapes are considered to be a major source of phenolic compounds as compared with other fruits. To improve the quality of table grapes, some techniques like thinning can be used. In addition, grape cultivars with distinct characteristics are directly linked to its phenolic profile. This study aimed to identify and quantify the phenolic compound profile and yield of the hybrid 'BRS Vitoria' seedless table grape under different bunch densities, using a combination of solid-phase extraction (SPE) methodologies and analytical high-performance liquid chromatography-diode array detector with tandem mass spectrometry (HPLC-DAD-ESI-MS/MS). A trial was carried out in 2016, in a commercial vineyard at Marialva, state of Parana (South Brazil). Three weeks after anthesis, the following bunch densities were evaluated: 4.0, 4.5, 5.0, 5.5, and 6 bunches per m² (corresponding to an estimation of 16, 18, 20, 22, and 24 tons ha^-1). The randomized block design was used as a statistical model with each treatment was replicated four times, with one vine per plot. Different characteristics were evaluated at harvest, e.g., soluble solids content (SS), total acidity (TA), maturation index (MI = SS/TA), bunch and berry masses, yield, as well hydroxycinnamic acid derivative (HCAD), anthocyanin, flavonol, and flavan-3-ol contents by HPLC-DAD-ESI-MS/MS analysis. The evaluated bunch densities did not interfere with the physicochemical characteristics of the berries, such as SS and MI. Under the density of 6.0 bunches per m², the highest yield of 25 tons ha^-1 was reached. Under all bunch densities, the phenolic profile presented the same compounds, but at different concentrations. Under a density of 5.0 bunches per m², the compounds belonging to the anthocyanin and flavonol families were present in high concentrations. In contrast, at the densities of 4.0 and 4.5 bunches per m², there was a reduction in the flavan-3-ol content. With respect to stilbenes, only the trans-piceid and its cis- isomer were detected. However, their concentrations had no significant influence on the evaluated bunch densities.

Changes in global aroma profiles of Cabernet Sauvignon in response to cluster thinning

Cluster thinning (CT) is a common practice to prevent overcropping in viticulture. CT affects vine balance between vegetative and productive growth and further modifies grape composition. This study investigated the effects of cluster thinning treatments applied at pea-size stage (CT-AF) and the onset of veraison (CT-V), respectively, on volatile compounds of Cabernet Sauvignon in two seasons (2013-2014). The experimental vineyard was located in the north-west of China with semi-arid and monsoon climate. CT exhibited limited effects on the evolutions of volatile compounds. CT-AF exhibited an inhibition on 6-methyl-5-heptene-2-one accumulation. There were no differences in terpene concentrations between CT-treated and control grapes regardless of CT time. Regarding C₆/C₉ compounds and their derivatives, CT-AF decreased nonanal concentration whilst CT-V increased (Z)-3-hexen-1-ol concentration. Additionally, there were increases in nonanal, (E)-2-hexen-1-ol, (Z)-2-hexen-1-ol and (Z)-3-hexen-1-ol concentrations in grapes with delayed CT. Among benzene derivatives, earlier CT resulted in lower phenol concentrations.

Impact of cluster thinning on transcriptional regulation of anthocyanin biosynthesis-related genes in 'Summer Black' grapes

Cluster thinning is an agronomic practice that strongly affects anthocyanin biosynthesis in the skin of grape berries. However, the impact of cluster thinning on anthocyanin biosynthesis has not been fully elucidated at the molecular level. Here, we investigated its effects on the berry quality, the biosynthesis of anthocyanins, and the expression levels of related genes from the onset of véraison to harvest in 'Summer Black' grapes. It was observed that the total soluble solid and anthocyanin content in berry skin significantly increased under cluster thinning, whereas the berry weight and titratable acidity showed no differences from the beginning of véraison to harvest. The expression level of most anthocyanin biosynthesis-related genes was significantly up-regulated by cluster thinning from the beginning of véraison and was higher at its end compared to the control. Up-regulation of flavonoid 3',5'-hydroxylase (F3'5'H) and O-methyltransferase (OMT) expression, and down-regulation of flavonoid 3'-hydroxylase (F3'H) expression were observed, which might be the cause of shift in the anthocyanin profile. These findings provide insights into the molecular basis of the relationship between cluster thinning and anthocyanin biosynthesis in the grape berry skin.

Aroma compounds in Ontario Vidal and Riesling icewines. II. Effects of crop level

Icewine is a dessert wine of substantial commercial value to the Canadian wine industry. Many grapegrowers crop icewine-designated vines at levels double those for table wines; therefore, the experimental objective was to ascertain whether reducing crop level might impact icewine chemical and aroma compound profiles. Three treatments [control (fully-cropped); cluster thin at fruit set to one (basal) cluster per shoot (TFS); cluster thin at veraison (TV)] were evaluated in randomized block experiments for Riesling and Vidal over two seasons (2003-04; 2004-05). Treatments differed in must pH and titratable acidity (both years) and although wines differed for most standard chemical variables, no clear trends existed. Vidal icewines had the highest aroma compound concentrations in the control and TV (2003) and in TFS (2004). Most Vidal aroma compounds differed with crop level: 17/24 (2003) and 23/24 (2004). Vidal odor activity values (OAVs) were highest for: β-damascenone, ethyl octanoate, cis-rose oxide, 1-octen-3-ol, ethyl hexanoate, isoamyl acetate (2003); β-damascenone, 1-octen-3-ol, ethyl octanoate, cis-rose oxide, and ethyl hexanoate (2004). Principal component analysis (PCA) found β-damascenone, ethyl 2- and 3-methylbutyrate, ethyl isobutyrate, ethyl butyrate and 1-heptanol correlated and associated with the control (2003), but most compounds were positively loaded on PC1 and associated with replicate, not crop level (2004). All Riesling aroma compounds differed with crop level (2003) and 22/23 (2004). Both years, most aroma compounds were highest in TV and lowest in TFS wines. Riesling OAVs were highest for: β-damascenone, ethyl octanoate, and ethyl hexanoate (2003, 2004); cis-rose oxide was highly odor potent (2004). PCA of Riesling showed most compounds loaded on PC1 and associated with TV wines (2003). Freeze/thaw events in November/December appeared more important in aroma compound development than adjustment of crop level, and it is therefore concluded that reduction of crop level in Vidal and Riesling vines would not substantially impact icewine aroma composition.