Background and Aims Grafting in viticulture has been essential since the advent of the phylloxera crisis at the end of the 19th century, but relatively little is known about the relevance of the quality of the connection at the grafting junction on the behaviour of grafted grapevines. Methods and Results An experimental procedure comparing omega grafted vines with complete alignment of the scion and the rootstock (CA) and vines with partial alignment (PA) was developed. Three complementary trials were carried out in the nursery, in the field and under controlled conditions. The CA vines increased the success rate in the nursery. Vine growth was significantly affected by the alignment between the rootstock and scion both in the nursery and in their first year of establishment in a commercial vineyard and in a potted trial, although these differences dissipated in years 2 and 3 under commercial vineyard conditions. The CA graft also maintained a higher level of leaf gas exchange, but such differences did not correspond to those in the hydraulic conductivity across the graft union itself. Conclusions The degree of alignment of the grafted vine material affected vine development, but a better understanding of the role of vascular connections in different graft types and qualities is needed. Significance of the Study To the best of our knowledge, this is the first scientific study that developed an experimental procedure for assessing the implication of the alignment at the grafting point on grapevine physiology and water use.< Réduire