Deciphering the ability of different grapevine genotypes to accumulate sugar in berries

Background and Aims: To analyse the genetic determinants of berry sugar content in grapevine varieties, a method that combined measurements of total soluble solids (TSS) from berries sampled at a fixed stage after veraison with data on the yield and the leaf area was tested. Methods and Results: Over three seasons, differences in TSS at harvest for Riesling and Gewurztraminer grapes were explained by differences in the veraison dates and in the fruit-to-leaf ratios. TSS, yield and leaf area were also evaluated for 120 genotypes, which were progeny from a cross between Riesling and Gewurztraminer. Thermal timescales (degree-days) proved relevant for describing sugar accumulation in the parent varieties, and when berries were sampled at a fixed heat sum after veraison in the progeny, the genotypic variability of sugar content was considerably reduced compared with the measurements on the same date at the end of the season. A negative relationship between the fruit-to-leaf ratio and the sugar content was also detected in the progeny. Conclusions: The evolution of TSS during berry ripening can be described using thermal timescales. Additionally, information on the yield and the leaf area needs to be integrated to analyse the behaviour of genotypes. Significance of the Study: A method to characterize the genotypic effect on fruit sugar accumulation after eliminating the contribution of veraison dates and crop load was proposed.