Selecting varieties best adapted to current and future climate conditions based on ripening traits

Aim: The aim of this study was to quantify key berry sugar accumulation traits and characterize their plasticity in response to climate variation from data collected from different cultivars over seven years from an experimental vineyard.

Methods and Results: Berry samples were collected weekly from different Vitis Vinifera (L.) cultivars at four replicate locations within a common-garden randomized complete block design from 2012-2018 in Bordeaux, France. A logistic model was parameterized to the sugar accumulation data and ripening traits were extracted. The variation in sugar accumulation traits were well explained by cultivar, year, and their interaction, highlighting the relative roles of genetic variation and phenotypic plasticity. Sugar accumulation traits themselves were affected by antecedent and concurrent climate factors such as temperature, photosynthetically active radiation, and vine water status, whether before, or after mid-véraison. In addition, other traits such as berry weight at mid-véraison, and date of mid-véraison had an important influence on sugar accumulation traits. Further, the relative importance of these factors varied significantly by cultivar. More research is needed to unravel the exact mechanisms underlying the differential genotypic responses of traits to these factors.

Conclusions: 

The variations in sugar accumulation traits were well explained by cultivar, year, and their interaction, highlighting the relative roles of genetic variation, climate factors, and phenotypic plasticity. Sugar accumulation traits were found to be affected by antecedent and concurrent climate factors both before and after mid-véraison. The relative importance of these factors varied significantly by cultivar. In this study we focused only on sugar accumulation traits. Sugar is, however, only one of many determinants for grape cultivar suitability in wine regions. Other traits include, but are not limited to, water use efficiency, photosynthetic capacity, yield, and berry composition. 

Significance and Impact of the Study: Climate change induces excessively high sugar levels in grapes, resulting in wines with increased alcohol content. It also results in earlier ripening, moving the ripening period to a part of the season where climatic conditions are not optimum for producing high quality wines. Variability among cultivars is a precious resource to adapt viticulture when environments change. This study highlighted the relative roles of genetic variation and phenotypic plasticity to environmental conditions in the variation of sugar accumulation traits. Moreover, it shows that a multi-trait approach is required to study wine grape ripening to select varieties in a context of global change.