Predictive Breeding: Impact of véraison (onset of ripening) on wine quality

Abstract

Grapevine breeding focuses on high wine quality and climate-adapted grapevine varieties with fungal disease resistances to be cultivated in a pesticide-reduced and sustainable viticulture. While a number of resistance loci can be identified in marker-assisted selection (MAS), no adequate tools for an early detection of the highly important wine quality potential is available up to now. This is mainly due to the enhanced complexity of multifactorial traits and interrelated parameters. Implementation of quality traits to MAS has the potential to improve grapevine breeding efficiency considerably and is demanded by breeders. These traits bear the potential for an early negative selection of poor quality genotypes in recently germinated seedlings and could lead to an early identification of high quality genotypes in advanced breeding stages. In recent decades, the effects of global warming led to a well-documented earlier flowering and ripening in viticulture with strong impact on wine quality. A number of traditional grapevine cultivars show the tendency to ripen too early in most years in the wine growing regions of Germany. To deliver future climate adapted cultivars this has to be considered during selection.
The véraison called onset of ripening is characterized by berry softening, onset of sugar and aroma accumulation, switch from organic acid formation to degradation, and for red cultivars start of coloration. Thus, véraison marks the transition from berry growth to berry ripening.
Date of véraison was recorded for a ‘Calardis Musqué’ x ‘Villard Blanc’ white wine F1 population with 150 genotypes. Data of 17 individual datasets obtained over a period of 22 years and from three different field plots were included. Based on a genotyping-by-sequencing (GBS) approach and a novel bioinformatics pipeline to deliver highly informative haplotype-based markers (HBMs), a high density genetic map with 2,260 genome-wide distributed HBMs was used for quantitative trait loci (QTL) analysis.
The major QTL for véraison, Ver1, on chromosome 16, was validated. The improved data density and a locus-specific marker-densing (LSMD) approach narrowed down the postulated region from about 5 Mb with hundreds of genes to 174 kb encoding 13 genes including one strong candidate gene. Minor QTLs were observed on chromosomes 2, 7, 13, 17, and 18.
This knowledge is the starting point to develop suitable tools like MAS markers for grapevine breeding to select genotypes with the desired ripening time. In addition, unraveling the impact of véraison on quality determining constituents such as organic acids, sugars and aroma compounds will allow us to breed in a more targeted approach those new varieties, which are better adapted for future climatic conditions.