Soil fertility and confered vigour by rootstocks

The adaptation of rootstock to scion variety and soil determines largely the control of the vegetative growth for grapevine. Many experiments were performed in the vineyard to classify the rootstocks according to their soil adaptation and to their effect on vine vigour. So far there are no data describing the course of appearance of rootstock effects after plantation. Moreover the underlying mechanisms of conferred vigour remain largely unknown. An experimental vineyard was planted with 2 varieties (Merlot and Cabernet-Sauvignon) grafted onto 3 known rootstocks (Riparia Gloire de Montpellier, SO4 and 110R) in a gravely soil from Bordeaux area. Two years after plantation, a high level of soil fertility was created on half of the plot, by adding 100 N units at spring and watering the vines during summer. Soon after plantation and during 4 years, developmental data (phenological stages, shoot growth, shoot diameter, leaf area, pruning wood weight, bud fertility and yield) and physiological data (water status, leaf gas exchanges, mineral analysis, stored carbohydrates) were collected all through the seasons.

It was observed that the rootstocks affected vine vegetative growth early after plantation, before the vines bared any crop and even in the plot where the fertility was high. Parameters describing vegetative growth (shoot growth rate, shoot diameter, leaf area) and biomass accumulation were highly correlated. Significant differences between rootstock / scion combinations were recorded on leaf gas exchanges, stored carbohydrates and water status. However these effects are closely related to the vegetative and reproductive development of the vines. Multidimensional analysis of the data showed the effects of scion variety, rootstock and soil fertility. The invigorating effect of Riparia Gloire de Montpellier remains regardless of soil fertility and scion variety. However this effect is stronger when the scion is Cabernet-Sauvignon. The conferred vigour seems to be related to a very early interaction between rootstock and scion, which occurs regardless of environmental conditions. The determinism of this interaction does not seem to be related to the water and nitrogen status of the vines.