Bacterial community in different wine appellations – biotic and abiotic interaction in grape berry and its impact on Botrytis cinerea development

This study focuses on investigating the effects of climate change on the plant physiology and berries of Vitis vinifera cv “Monastrell” in a commercial vineyard managed organically in Southeastern Spain (Jumilla, Murcia). For this purpose, open top chambers and rainout shelters were employed to simulate warming (~2-7 ºC, W) and rainfall reduction (~30%, RR) respectively. Additionally, a combination of both treatments (W+RR) was employed. Vines without either top chambers or rainout shelters were considered as control (C). The experiment was established in February of 2023. Predawn leaf water potential (measured using a pressure chamber), stomatal conductance (assessed with a porometer at mid-morning) and leaf chlorophyll and flavonoid content (measured using the Dualex® leaf clip sensor) were analyzed at veraison (5 months after the installation of structures).

Alteration of sap pH is one of the first chemical changes that occurs within the xylem vessels of plants exposed to drought. Xylem sap acidification accompanied by the accumulation of soluble sugars has been recently documented in several species (Sharp and Davis, 2009; Secchi and Zwieniecki, 2016). Here, Vitis vinifera plants of the anysohydric cultivar Barbera were exposed to either short (no irrigation; SD) or to prolonged drought (continual reduction of 10% water; PD). When comparable severe stress was reached, the potted grapes were re-watered. SD was characterized by fast (2–3 days) stomatal closure and high abscisic acid (ABA) accumulation in xylem sap (>400 μg L−1) and in leaf. In PD plants, the rise in ABA levels was considerably diminished.

Obtaining high-quality RNA from grape tissues, including berry pulp, berry skins, stems, rachis, or roots, is challenging due to their composition, which includes polysaccharides, phenolic compounds, sugars, and organic acids that can negatively affect RNA extraction. For instance, polyphenols and other secondary metabolites can bind to RNA, making it difficult to extract a pure sample. Additionally, RNA can co-precipitate with polysaccharides, leading to lower extraction yield. Also, sugars and organic acids can interfere with the pH and ionic properties of the extraction buffer. To address these challenges, we optimized a protocol for RNA isolation from grape tissues.

Over the last decade, the use of non-Saccharomyces yeasts in the winemaking process has been re-assessed and accepted by winemakers. These yeasts can be used to achieve specific objectives such as lowering the ethanol content, preventing wine spoilage and increasing the production of specific aroma compounds. Since these species are unable to complete alcoholic fermentation, strategies of co- and sequential inoculation of non-Saccharomyces and Saccharomyces cerevisiae have been developed. However, when mixed starter cultures are used, several parameters (e.g. strain yeast, inoculation timing and nutrient competitions) impact the growth of the individual yeasts, the fermentation kinetics and the metabolites/aroma production. In particular, competition for nitrogen compounds could have a major impact, potentially leading to sluggish fermentation when the yeast assimilable nitrogen (YAN) availability is low. Moreover, many aroma compounds produced by the yeasts are directly produced and influenced by nitrogen metabolism such as higher alcohols, acetate esters and ethyl esters which participate in the organoleptic complexity of wine.

Detailed geological analyses of a plot belonging to the « AOC Gaillac » area have been carried out. This plot belongs to the left bank terraces of the Tarn River which coinciding with one of the three main terroirs of the AOC area. It is localised on the rissian-aged (≈ 200 000 yrs B.P.)