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Varietal differences in solute accumulation and grape development

Abstract : Until recently, varieties used for wine production (mainly V. vinifera) have been selected for high sugar accumulation and secondary metabolism compounds (aromas, tannins, anthocyanins). Some climate change parameters (temperatures, CO2) accentuate the trend towards higher sugar levels at harvest, resulting in more alcoholic wines. The increase in wine alcohol content is a global phenomenon, with annual increases of 0.16%. This alters the qualitative profile, in particular by impacting the alcohol/acidity balance and poses a problem for consumer health.The grape is a non-climacteric fleshy fruit that develops in two phases. The first is the herbaceous phase during which malic and tartaric acids accumulate mainly accumulate. During this phase, the berry grows by mitosis and vacuolar expansion. The second phase of growth is associated with the massive import of hexoses, water and potassium. At the end of the second growth phase, the phloem stops unloading and the berry concentrates its main metabolites by evaporation. Some oenological practices make it possible to reduce the sugar content of must or alcohol wines content (CEE-606/2009 and CEE-53/2011), but are partial or costly and can have an impact on the wines quality. Cultivation practices do not sufficiently modify the development of the grape to be effective, except that they degrade the quality potential of the harvest. In the long term, the most promising approach is the variety selection.The latter aspect was addressed in the thesis project. First, new phenotyping strategies/tools were developed to characterize grape development. Then, the diversity for the accumulation of primary metabolites in grapes (V. vinifera) or that can be generated by crossing with the microvine was analysed. In the last part, the physiological characterisation of genotypes resulting from a cross between V. vinifera and M. rotundifolia with a low sugar accumulation character during grape ripening was further developed.The main results of this work indicate:1) It is possible to assess the development of a berries population both in asynchrony (densimetric baths) and in heterogeneity (Dyostem). The colour of the fruit was not a good indicator of the beginning of ripening, appearing 1 to 5 days after the first signs of berry softening. In addition, monitoring at the berry population level has shown that for fine analyses, it is preferable to analyse the single fruit.2) There is a great diversity in V. vinifera with regard to the composition of primary berry metabolites and their dilutions. The possibility of independently segregating the accumulation of water, sugars, acids and cations was revealed, opening up interesting prospects for varietal innovation.3) Analysis of the low sugar concentration trait in descendants of V. vinifera and M. rotundifolia shows that this characteristic does not result from a limitation or delay in accumulation or from greater heterogeneity/asynchrony of the berries. The results suggest that there are mechanistic differences between growth level and osmotic pressure of the fruit during maturation between genotypes. This discovery raises many questions: are there differences in the cell wall structures or their associated enzymes? Are berry cells of low sugar genotypes larger or more numerous than traditional varieties?Two of these descendants were crossed with the microvine to detect the associated QTLs to this trait in order to identify the functions controlling this agronomic interest trait.
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Antoine Bigard. Varietal differences in solute accumulation and grape development. Agricultural sciences. Montpellier SupAgro, 2018. English. ⟨NNT : 2018NSAM0063⟩. ⟨tel-02542686⟩

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