Deciphering the genetic variability of berry sugar content in grapevine cultivars
Duchene, E. | Dumas, V. | Jaegli, N. | Merdinoglu, D. | Dai, Z.
The genetic determinism of sugar content was studied over three growing seasons in the vineyard in progeny from a 'Riesling' × 'Gewurztraminer' cross. Because both phenological stages and fruit-to-leaf ratios influence the sugar content of the berries, we tested a method of evaluation of genotypic traits that integrates for each genotype information on veraison date, leaf area and yield level. We showed that the genetic variability of sugar content measured at harvest is highly reduced when berry sampling is performed at a given heat sum after veraison and when measured values are corrected according to the fruit-to-leaf ratios observed. In our data, a later veraison date and a higher fruit-to-leaf ratio in 'Riesling' could explain its lower sugar content at harvest when compared to 'Gewurztraminer'. An analytical model describing the carbon and water fluxes in the berry showed that a coefficient related to the non-sugar use of carbon imported in berries was different between the two cultivars. This coefficient was also estimated for genotypes of the progeny and differences between genotypes were observed. This study confirms that phenological stages and crop load are major drivers for creating variability in berry sugar content but that they cannot totally explain the genetic variability. Other physiological processes at the berry level have to be considered, and we provide here the first example of the related genetic variations in a progeny.
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