Grapevine grafting is an essential part of winemaking. We need the scion varieties to produce high-quality wines, but we also require the rootstocks to provide the necessary resistance against phylloxera and other pathogens or environmental factors. Grafting scion and rootstock varieties together produces the vines commercially available today—a complex, multi-season task performed by nurseries worldwide. Researchers in Spain investigated different grafting techniques by developing a new method for examining the newly formed xylem vessel connections one year after grafting.

Project layout
Tempranillo grafted onto 110 Richter was used. Four grafting techniques were investigated:

• Omega graft
• Full cleft
• Cleft
• Whip & tongue “lang-tong ent”

Various lab techniques were used to highlight and isolate open spaces or necrotic tissue (red), existing xylem vessels pre-grafting (cyan and navy blue), and newly formed xylem vessels one year after grafting (white) using micro–CT scans and specialised software to create 3D images. Three vines were scanned for each graft type. The vines used all passed the “thumb” test and meet all standards to be sold commercially.

Results

• All functional xylem vessels connecting the scion and rootstock are exclusively located in newly formed wood. Nowhere
• In some Omega and Full Cleft grafts, the xylem connections are not continuous around the entire circumference of the graft union but form a more heterogeneous pattern, with more concentrated xylem connections forming underneath the scion bud.
• This highlights the positive effect the buds have on graft union formation.
• In the three Cleft grafts, functional xylem vessels only formed towards the base of the scion.
• In the Whip & Tongue grafts, there was generally a good distribution of xylem vessels around the circumference of the graft union. However, some regions had very little callus tissue.
• The amount of air spaces or necrotic tissue was significantly less in Omega graft unions compared to Whip & Tongue grafts.

Significance of the study
This work shows that different grafting techniques each present unique advantages and challenges, but no single method is perfect. Additionally, note that this work is based on newly developed xylem tissue and does not focus on phloem development. The substantial amount of dead tissue and open spaces within the graft union highlights the importance of managing trunk disease pathogens within the propagation process. Methods such as hot water treatment and other possible ways to counter trunk diseases in planting material need to be widely adopted and further developed.

Reference:

Camboué, M., Janoueix, A., Spilmont, A.-S., Mathieu, G., Ollat, N., Santesteban, L. G., & Cookson, S. (2025). Visualising xylem vessels connections formed one year after grafting using different techniques. OENO One, 59(3). https://doi.org/10.20870/oeno-one.2025.59.3.9148