Influence of irrigation on vine plant behaviour and on wine quality in red wine rootstocks cultivated in central Wallis, Switzerland

Irrigation experiments conducted in Leytron (Wallis, Switzerland) on the red wine rootstocks Pinot noir, Gamay, Diolinoir and red Humagne led to confirmation of the highly positive effect of moderate water stress on grape ripening and wine quality. A gradual and moderate restriction in water supply at the time of fruit ripening resulted in a slowing down of plant growth and favoured the accumulation of sugar in berries. The resulting wines had a deeper colour, were richer in phenol compounds and preferred by wine tasters. Under conditions of greater and longer water stress, these advantages tended to be cancelled out. A close relationship was established between the theoretical water deficit and water stress levels measured in the vineyards, which could be exploited as a tool to decide if an irrigation is required.