Bud break and cytokinin concentration in bleeding sap of Rosa hybrida as affected by the genotype of the rootstock

Grafting Rosa hybrida Madelon on six rootstock genotypes revealed that growth of the scion was affected by the genotype of the rootstock. If rootstocks would mediate scion growth via their cytokinin production, it might be possible to improve the performance of a rootstock by exogenous application of cytokinins. Indeed, benzyladenine (BA) application was found to stimulate the number of bottom breaks, mainly on the low-yielding rootstocks Vivaldi and Madelon. To test the hypothesis that a rootstock that induces earlier bud break of the scion supplies more cytokinins to the shoot, cytokinin levels in bleeding sap of Vivaldi and the vigorous rootstock Multic were followed during plant development. Bud break of the axillary shoots was not affected by the genotype of the rootstock, but bottom breaks appeared earlier when Madelon was grafted on Multic than on Vivaldi. The concentration of zeatin riboside (ZR) in bleeding sap of Madelon/Multic combination plants was high at axillary bud break, decreased when the axillary buds grew out, increased thereafter until the bottom breaks appeared, and decreased again. The ZR concentration in bleeding sap of Madelon/Vivaldi plants was considerably lower than that of Madelon/Multic plants, but showed more or less the same pattern. Apical dominance in rose combination plants during their development is discussed in terms of auxin and cytokinins.