EFFECT OF ROOTSTOCK ON ORGANIC ACIDS IN LEAVES AND BERRIES AND ON MUST AND WINE ACIDITY OF TWO RED WINE GRAPE CULTIVARS 'MALBEC' AND 'NÉGRETTE' (VITIS VINIFERA L.) GROWN HYDROPONICALLY

A hydroponic culture experiment was carried out during two successive seasons on five-year old grapevines ‘Négrette’ and ‘Malbec’. ‘Négrette’ own-rooted vines were compared with three rootstocks: 3309 Couderc (3309 C), SO4 and 101-14 and ‘Mabec’ own-rooted vines were also compared to three rootstocks : 3309 C, SO4 and Riparia Gloire. The results obtained show that there is a significant effect of rootstock on cationic contents in leaves (blooming and veraison) and in musts. ‘Négrette’ has a higher capacity to accumulate K in leaves and berries than ‘Malbec’. The 3309 C presented the lowest K contents for these two cultivars. Rootstocks present also a significant effect on tartaric and malic acids contents in berries. ‘Malbec’ presents higher tartaric acid contents in berries than ‘Négrette’. In must and wine, ‘Malbec’ has higher tartaric acid content than ‘Négrette’. ‘Malbec’ has a higher titratable acidity. These two cultivars grafted onto 3309 C as rootstock presented the highest acidity of must and wine. Positive correlations were established between pH level of musts and potassium contents respectively ‘Malbec’ and ‘Négrette’ r = 0.898 and r = 0.803. However, for wine, these correlations were lower. Indeed, tartaric acid/K ratio presented negative correlation with musts pH level (‘Malbec’ - r = - 0.974 and ‘Négrette’ - r = - 0.941) which was lower than the correlation with wines pH level after cold stabilization (‘Malbec’ r = - 0.522 and ‘Négrette’ r = - 0.675).