Carbohydrate profiles in the graft union of young sweet cherry trees grown on dwarfing and vigorous rootstocks

In composite (scion–rootstock) dwarfing fruit trees, an overgrowth at the graft union is often observed, the severity of which is correlated with degree of dwarfing. The graft union of dwarfing sweet cherry (Prunus avium L.) rootstocks may limit soluble sugar transport or starch mobilization, leading to localized accumulation. Soluble sugars and starch were measured in the tissues surrounding the graft union of young ‘Rainier’ (2002) and ‘Lapins’ (2003) sweet cherry trees on ‘Gisela 5’ (‘Gi 5’; dwarfing) and ‘Colt’ (vigorous) rootstocks. Separate rootstock shank, rootstock, graft union, and scion tissues were analyzed for both starch and soluble sugar content throughout the growing season in both years. Starch concentrations did not vary among locations within the graft union for ‘Rainier’ on either the dwarfing or vigorous rootstock, or for ‘Lapins’ on the dwarfing stock. However, for ‘Lapins’ on ‘Colt’, starch was highest in the rootstock shank and declined vertically (rootstock shank ≫ rootstock > union > scion). Soluble sugar concentrations were generally similar to or higher in scions on ‘Gi 5’ than on ‘Colt’, and were similar to or lower in the rootstock and rootstock shank on ‘Gi 5’ than on ‘Colt’. Results suggest that rootstock has a significant effect of localized accumulations of carbohydrates above and within the graft union of ‘Gi 5’ and below the graft union of ‘Colt’.