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Impact of the carbon source/sink balance on glycosylated aroma precursor accumulation in grapevine fruit (Vitis vinifera L.)

Abstract : Aroma compounds are secondary metabolites that play a key role in grape quality. Terpenes, C13-norisoprenoids, phenols and non-terpenic alcohols are the most important aroma compounds in grapes and can be accumulated as free volatile or glycoconjugated molecules. The non-volatile glycosylated aroma precursors (GAP) group is the largest one, and it is present in all varieties of Vitis vinifera (L.), the most widely-used species for wine production. Agronomic practices such as irrigation, training systems, leaf removal and bunch thinning can impact the plant and fruit development. The modification of the source/sink relationship (S/S) with the scope of increasing the grape quality, is very common between viticulturists. These practices include bunch thinning, pruning, and the election of the number of buds/plant. Bunch thinning, a very extended practice in viticulture and which directly impacts on S/S, is one of the less researched practice regarding GAP. In many cases, DOC and IGT production protocols include a limit in the fruit yield per hectare. Then, viticulturists regulate yield by managing number of buds/hectare and/or by fruit thinning.The main objective of our work was to analyze the impact of the modifications of S/S balance on the biosynthesis of GAP. GAP are chosen in this research because: 1) they are present in every cultivar of Vitis vinifera, 2) they represent the biggest source of potential aromatic molecules, and 3) because these molecules incorporate glycosyl groups, their accumulation depends on the supply of carbohydrates and potentially on the carbon balance of the plant. The main objective of our work concerned the study of the impact of the S/S ratio on the biosynthesis of GAP, and its possible modulation depending on the genotype. Five questions were addressed: 1) Influence of the genotype on in the biosynthesis of GAP and its accumulation. The objective is to analyze the variability of GPA concentration at a given maturity stage among genotypes, including a set of varieties of V. vinifera (Marselan, Grenache, Muscat, Cabernet Sauvignon, Syrah and Chardonnay) and hybrids. V. vinifera x Muscadinia rotundifolia (G5). 2) Influence of the year on S/S balance and GAP concentration. 3) The impact of the S/S balance on the biosynthesis of GAP expressed in concentration (µg/L) and in quantity (µg/berry) as a function of grape development. 4) The relationship between primary and secondary metabolism (GAP and anthocyanins) and their modulation as a function of S/S balance. 5) Influence of the thinning date on the dynamics of GAP biosynthesis.The results showed that levels of glycosylated aromatic compounds varied according to genotype. Varieties whose grapes contain terpenic compounds (Muscat à petits grains blancs and the V. vinifera x Muscadinia rotundifolia G5 hybrid) showed the highest levels of GAP in both concentration and amount per fruit. These genotypes showed the highest values of GAP/sugar ratio. In general, genotypes producing non-colored berries had higher GAP/sugar ratios than colored berries. Despite strong inter-annual variation, the impact of the S/S ratio on GAP biosynthesis was found to be genotype-dependent.Thus, the GAP concentration was not affected during the modification of S/S in Cabernet-Sauvignon, while Muscat and Syrah showed large variations in GAP/berry contents as a function of the S/S ratio. The thinning date was also an important modulating factor in the increase of GAP, but varies according to genotype. In general, a significant decrease in the amount of primary metabolites accumulated in grapes is required to significantly increase the biosynthesis of secondary metabolites. This gain is very notable for anthocyanins, which are the most abundant carbon compounds after the primary metabolites (sugars and organic acids) in grapes. With regard to aromatic precursors, the impact is more moderate regardless of the family of glycosylated compounds.
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Hubert Alem. Impact of the carbon source/sink balance on glycosylated aroma precursor accumulation in grapevine fruit (Vitis vinifera L.). Agricultural sciences. Montpellier SupAgro, 2018. English. ⟨NNT : 2018NSAM0062⟩. ⟨tel-02542663⟩

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