Visualising xylem vessels connections formed one year after grafting with 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 investigates the three-dimensional (3D) structure of the graft interface produced by commonly used techniques, namely, the omega, full cleft, cleft, and Whip and Tongue. X-ray micro-computed tomography was used to determine anatomy of the graft union based on tissue x-ray density and functional xylem vessels were labelled with the contrast agent. The total volume of the graft interface, the volume of air spaces/necrotic tissues and the distribution of functional xylem vessels was studied. Functional xylem vessels connect the scion and the rootstock in all grafting types, but in some grafts, this connection is not continuous around the entire circumference of the graft interface. We found that the proportion of air spaces/necrotic tissues relative to the graft interface volume was not affected by grafting type. Omega grafts were found to be more compact, with shorter graft interfaces and as a consequence a smaller absolute volume of air spaces/necrotic tissues at the graft interface. By combining 3D morphological and functional analysis, this study presents a step forward in addressing the questions facing modern viticulture.