Understanding and mapping rotundone spatial variability in Vitis vinifera L. c.v Duras

Recent research works highlighted large variability in rotundone concentration-the main compound responsible for peppery aroma in red wines-within a vineyard block associated with variation in land underlying the vineyard and vine water deficit. In order to further study and determine practical ways to map rotundone spatial variability, a study was carried on a 0.41 ha Duras vineyard from the South West of France under oceanic climatic influence. The smart point method was used and in order to optimize vineyard sampling, variability in vine architecture of the plot was assessed through measurements of trunk circumference (TC). On the basis of the three classes of TC obtained, six smart points made of 50 vines were positioned and followed independently over the vine growing season and winter dormancy for shoot elongation, stem water potential (Ψ stem), mineral uptake (petiole analysis and Dualex® measurements), airborne multispectral video imagery (NDVI), fruit quality, pruning wood weights (Physiocap® and manual weighing) and yields at harvest. At each smart point, rotundone was measured in wines obtained by microvinification techniques (1 L Erlenmeyer). Differences between smart points were very weak from an agronomic standpoint. However, a few plant physiological indicators (i.e. Ψ stem, Dualex® measurements) allowed discriminating vine performances. Despite this very low variability between plant and fruit measured variables (including those related to grape and wine quality but excluding TC), rotundone concentration was on average more than 50% higher in the wines from the high TC area. Thus, our data set suggests that a link exists between plant architecture (TC) and rotundone, and that TC can be used to approach rotundone spatial distribution. Our results also tend to strengthen the hypothesis that rotundone is very sensitive to fine variations of grapevine water status.