Karine Pedneault

The climate crisis is changing temperature regimes worldwide, threatening global viticulture and wine production, as temperature is a primary driver of grape development. In Atlantic Canada, temperatures are projected to increase, inducing premature grape ripening. This can impact their biochemical profiles and, consequently, the quality of the vines, in terms of plant health and fruit yield, and therefore the quality of the wines produced. Temperature is also a key factor in determining the composition fungal communities on the leaves (phyllosphere) and fruits (carposphere) of grape vines. Therefore, to better understand how these communities might change under potential future temperature regimes, we experimentally manipulated grapevines (Vitis sp. cv. L’Acadie blanc) in the field. We used on-the-row mini-greenhouses to increase the temperature at different developmental or phenological stages of the fruits, and across the whole season. Phyllosphere and carposphere were sampled at four developmental stages, their DNA was extracted, and the fungal communities were identified via ITS metabarcoding. We found that phyllosphere and carposphere had significantly different community composition, which remained relatively stable throughout plant development. Increased temperature treatments had the most significant effect on fungal phyllosphere communities; we observed that phyllosphere samples exposed to higher temperatures before the onset of ripening maintained fungal communities with higher species richness throughout development. Our analysis showed that the increase in fungal diversity among phyllopshere communities corresponds to enrichments in potential phytopathogenic fungal taxa. However, this increase in phyllosphere fungal diversity was not conserved at other growth stages when the leaves developed at higher temperatures for the whole season. The results of this study will contribute to better understanding the impact of the climate crisis on grapevine phyllosphere and carposphere fungal community composition and assembly. This will allow producers to better adapt to climate variability and to better understand the role that these communities could play on grapevine health.

The climate crisis is changing temperature regimes worldwide, threatening global viticulture and wine production, as temperature is a primary driver of grape development. In Atlantic Canada, temperatures are projected to increase, inducing premature grape ripening, which can impact their biochemical profiles and, consequently, the quality of the vines and wines produced. Temperature is also a key factor in determining the composition and structure of resident fungal communities on the leaves (phyllosphere) and fruits (carposphere) of grape vines. Therefore, to better understand how these communities might change under potential future temperature regimes, we experimentally manipulated grapevines ( Vitis sp. cv. L’Acadie blanc) in the field. We used on-the-row mini-greenhouses to increase the temperature at different developmental, or phenological, stages of the fruits, and across the whole season. Phyllosphere and carposphere were sampled at four developmental stages, their DNA was extracted, and the fungal communities were identified via ITS metabarcoding. We found that phyllosphere and carposphere had significantly different community composition, which remained relatively stable throughout plant development. Increased temperature treatments had the most significant effect on fungal phyllosphere communities; we observed that phyllosphere samples exposed to higher temperatures before the onset of ripening maintained more diverse fungal communities throughout development. Our analysis showed that the increase in fungal diversity among phyllopshere communities corresponds to enrichments in potential phytopathogenic fungal taxa. However, this increase in phyllosphere fungal diversity was not conserved at other growth stages when the leaves developed at higher temperatures for the whole season. The results of this study will contribute to better understanding the impact of the climate crisis on grapevine phyllosphere and carposphere fungal community composition and assembly. This will allow producers to better adapt to climate variability and to better understand the role that these communities could play on grapevine health.

Northern conditions are challenging for grape and wine producers. To cope with these challenges, the use of early ripening interspecific hybrid Vitis sp., such as Seyval blanc and Vandal-Cliche, is often preferred to traditional V. vinifera. However, knowledge about cultural practices suitable for interspecific hybrid varieties are still scarce, especially regarding their impact on profiles of volatile compounds and the sensory perception of berries. In this study, the impact of cluster thinning and harvest date on grapevine physiology, must chemical composition and berry sensory attributes of Seyval blanc and Vandal-Cliche was investigated. Three crop loads (100 %, 70 % and 40 % crop) and three harvest dates corresponding to pre-maturity, maturity, and post-maturity were assessed in 2012 and 2013. Cluster thinning significantly decreased the yield of Vandal-Cliche, but not of Seyval blanc, for which it instead improved fruit set without affecting yield. The impact of cluster thinning on must chemical composition was limited for both cultivars, although some significant changes were observed, especially in the cool season of 2013. Clear variations during ripening, in terms of technological parameters and aroma characteristics, were observed depending on the cultivars and the seasons. In Seyval blanc, C6-alcohols and C13-norisoprenoids decreased during ripening, while C6-aldehydes and linalool increased. In Vandal-Cliche, berries from the first and the last sampling dates of the warm season of 2012 showed the highest levels of C13-norisoprenoids, whereas berries from the last sampling date in the cold season of 2013 showed the highest levels of terpenes, C13-norisoprenoids and ethyl esters. Despite its limited impact on fruit chemical composition, cluster thinning significantly impacted the sensory perception of Vandal-Cliche berries in both years. Cluster-thinned berries had softer skin, sweeter and less acidic pulp, and fruitier skin and pulp aroma. Skin softness allowed excellent discrimination of the maturity of both cultivars during the two study years, suggesting that this descriptor could be a suitable maturity marker for these interspecific hybrid varieties. In summary, cluster thinning proves beneficial for enhancing fruit set in Seyval Blanc in a northern climate; however, its influence on fruit quality is minimal for both cultivars.

Volatile compounds (VCs) in grapevine berries play an important role in wine quality; however, such compounds and vine development can be sensitive to environmental conditions. Due to this sensitivity, changes in temperature patterns due to global warming are likely to further impact grape production and berry composition. The aim of this study was to determine the possible effects of different growing-degree day accumulation patterns on berry ripening and composition at harvest. An experimental field was conducted using Vitis sp. L'Acadie blanc, in Nova Scotia, Canada. Using on-the-row mini-greenhouses, moderate temperature increase and reduced ultraviolet (UV) exposure were triggered in grapevines during pre-veraison (inflorescence to the beginning of berry softening), post-veraison (berry softening to full maturity), and whole season (inflorescence to full maturity), while controls were left without treatment. Free and bound VCs were extracted from berries sampled at three different phenological stages between veraison and maturity before analysis by gas chromatography–mass spectrometry (GC-MS). Berries from grapevines exposed to higher temperatures during early berry development (pre-veraison and whole) accumulated significantly higher concentrations of benzene derivatives 2-phenylethanol and benzyl alcohol at harvest, but lower concentrations of hydroxy-methoxy-substituted volatile phenols, terpenes, and C₁₃-norisoprenoids than the control berries. These results illustrate the importance of different environmental interactions in berry composition and suggest that temperature could potentially modulate phenylpropanoid and mevalonate metabolism in developing berries. This study provides insights into the relationships between abiotic conditions and secondary metabolism in grapevine and highlights the significance of early developmental stages on berry quality at harvest.

Thiols are a group of highly potent aroma compounds found in many Vitis vinifera wines. In berries, thiols occur as precursors formed from a thiol attached to an amino moiety (e.g., cysteine and glutathione). Foliar sulfur and urea supplementation has been found to increase thiol precursors in V. vinifera berries. However, such data are still scarce for interspecific hybrid Vitis varieties, despite a growing interest in these cultivars. In this study, eight thiol precursors, 21 amino acids and glutathione (GSH) of seven white hybrid Vitis varieties collected in Quebec, Canada, were quantified by liquid chromatography with tandem mass spectrometry. Then, the impact of foliar sulfur and urea supplementation on thiol precursors of fully mature berries was tested on the Vitis sp. Vidal, using a complete randomised block design. Among the analysed thiol precursors, only the precursors of 3-mercaptohexan-1-ol (3MH) were detected, with glutathione-3MH (20-711 μg/kg berry fresh weight) as the main precursor in most studied varieties. Vidal samples had the highest concentrations of glutathione-3MH (313 μg/kg berry fresh weight) and GSH (17 mg/L in juice), but a large variability was found among the biological replicates. The amino acids proline, arginine, glutamine and alanine were the main amino acids found in Vidal, Frontenac blanc, Seyval blanc and Saint-Pepin respectively. Correlation analysis showed no significant relationship between thiol precursor and glutathione/amino acid content in berries. Foliar urea and sulfur supplementation had no impact on thiol precursor concentration in Vidal. However, a trend in a higher content of thiol precursors in berries treated with urea and sulfur compared to the control was observed on one of the two experimental sites.

Grape variety has a significant impact on wine flavan-3-ol and polysaccharide profile. The main objective of this work was to study differences in flavan-3-ol and polysaccharide diffusion from grape to wine during the fermentative alcoholic maceration of three Vitis sp. varieties: the cold-hardy hybrid varieties Frontenac and Frontenac blanc, and the V. vinifera variety Cabernet-Sauvignon. Polysaccharides from must and wine were precipitated by ethanol and quantified using the phenol-sulfuric method of Dubois. Flavan-3-ol concentration and profile were analysed by HPLC-FLD. Results showed that wines from Frontenac and Frontenac blanc had less oligomeric and polymeric flavan-3-ols than those from V. vinifera Cabernet-Sauvignon. Wines made from Frontenac also had a higher concentration in total polysaccharides. Preliminary results from GPC/SEC analyses suggested that Frontenac wine had a higher content in mannoproteins and rhamnogalacturonan-2 polysaccharides compared to the other studied varieties. Overall, wines of Frontenac showed the highest content in total polysaccharides, and the lowest content in condensed tannins. As polysaccharides are known to negatively impact wine perceived astringency, these results suggest that significant attention should be given to the polysaccharide composition of cold-hardy cultivars in the context of cold climate wine production. Such knowledge may help winemakers from cold climate areas to improve the winemaking processes and final wine composition when working with cold-hardy Vitis sp. varieties.Knowledge on interspecific hybrid polysaccharide and flavan-3-ol kinetic during the alcoholic fermentative maceration may help the winemakers from cold climate areas to improve winemaking processes and final wine composition.