Adapting wine production to climate change through the exploration of the diversity of Vitis vinifera cultivars

Abstract

Major factors involved in wine quality and typicity are soil type, climatic conditions, plant material (rootstock and cultivar), vineyard management practices and winemaking conditions. All these factors interact and growers optimize the output in terms of yield and quality by adapting plant material and management practices to environmental factors (soil and climate). Hence, plant material is region specific, because growers have selected the optimum rootstocks and varieties for their soils and climatic conditions through a long process of trial and error. Climatic conditions have always changed from year to year (the so-called vintage effect), but since three decades a long term trend is observed in most winegrowing regions towards increased temperatures and summer drought. This evolution raises the question whether region-specific plant material (in particular cultivars) will still be optimum in a warmer and dryer climate. To anticipate potential need for cultivar changes in the Bordeaux area, a trial encompassing 52 cultivars called “VitAdapt” was planted in 2009. Beside all references currently used in Bordeaux, the focus was laid on later ripening cultivars which are currently used in warmer regions. Every cultivar is planted with 5 replicates to take into account possible variations in soil composition. Phenology and grape composition from veraison to ripeness was monitored since 2012 and wines were made by micro vinifications in 2016 and 2017 for 20 cultivars. Wines were tasted by a panel of wine professionals familiar with Bordeaux wines and wines were scored for their typicity in relation to what can be expected for Bordeaux wine. Major varietal aroma compounds were analyzed in the wines.

Cultivars varied widely with regard to their precocity. The delay between the most early and latest cultivar is on average 28 days for bud break, 15 days for flowering and 39 days for veraison. A model called Grapevine Flowering Veraison (GFV) was developed and validated on the VitAdapt trial to predict the occurrence of these phenological stages from temperature data. Unsurprisingly, Bordeaux cultivars (and in particular Cabernet-Sauvignon) scored well with regard to Bordeaux wine typicity. Among non-Bordeaux cultivars which showed similar typicity, most were late ripening and had similar phenology, or later phenology, compared to the traditional Bordeaux cultivars. The analysis of key aroma compounds should allow to have a better understanding of the molecular basis of Bordeaux wine typicity and to group cultivars according to their aroma profile. This research will help Bordeaux wine growers to identify cultivars which can potentially be introduced in the Bordeaux cultivar-mix and thus provide a tool to continue to make highly quality, true-to-the-type Bordeaux wines in a changing climate.