Visualising xylem vessels connections formed one year after grafting using different techniques

Grapevine grafting is an important technique in viticulture and the formation of vascular connections between the scion and rootstock is essential for successful grafting. This study aims to compare the internal tissue organisation and functional xylem vessel connections in grapevine grafts that have passed the nursery quality selection process, produced using different commonly used grafting techniques: omega, full cleft, cleft, and whip & tongue. X-ray micro-computed tomography (micro-CT), a three-dimensional imaging technique, was used to observe the anatomy of the graft union based on tissue X-ray density, and functional xylem vessels were labelled with a contrast agent. This approach allowed us to study in 3D the total volume of the graft interface, the volume of air spaces/necrotic tissues, and the distribution of functional xylem vessels. The results show that functional xylem vessels connect the scion and rootstock in all grafting types, although in some grafts, this connection is not continuous around the entire circumference of the graft interface. Grafting type did not significantly affect the proportion of air spaces/necrotic tissues relative to the graft interface volume. Omega grafts were found to be more compact, with shorter graft interfaces and, as a result, a smaller absolute volume of air spaces/necrotic tissues at the graft interface. By combining 3D morphological and functional analysis, this study provides new insights into the internal quality of grapevine grafts depending on the grafting technique used.