Effect of potential crop on vine water constraint

It is important to quantify the effect of potential crop on vine water constraint in order to adapt vine-growing consulting and vine management to the Mediterranean climate conditions. Experiments were conducted during two years running (2006 and 2007) on varieties Grenache and Syrah in a situation of high water constraint in the Rhône Valley. Yields were regulated by hand cluster thinning before flowering or at the end of fruit-set, to 4 clusters per vine for the “low charge” modality and to 14 clusters per vine for the “high charge” modality. Yield measures were done during harvest: “low charge” modality varies from 30 to 50 % to the “high charge” modality. In these conditions, none of the predawn leaf water potential measures help identify an effect of potential crop on vine water constraint for Grenache (from flowering to harvest), for levels of water constraint up to –1,5MPa and for normal plot densities (4444 vines/ha). For Syrah, 2006 did not show significant differences between the two modalities, although 2007 seams so lead to a higher constraint for the “high charge” modality. The observation of the evolution of leaf water potential up to Sun mid-day shows that “high charge” modalities tend to express higher constraint than “low charge” modalities, although the differences are not significant.