Role of phenylurea cytokinin CPPU in apical dominance release in in vitro cultured Rosa hybrida L.

The effect of purine (BA) and phenylurea (CPPU) cytokinins on apical domina nce release in in vitro cultured Rosa hybrida L., cv. Madelon and Motrea wa s evaluated. Cv. Madelon shows stronger natural apical growth and fewer bra nches than cv. Motrea in vivo and in vitro. We examined the effects under t hree conditions, without the addition of the auxin IBA, in the presence of IBA, and in material pretreated with a pulse of IBA. Results were scored we ekly for 4 weeks. BA and CPPU stimulated axillary bud break, and higher num bers of open buds were recorded in the presence of CPPU. When CPPU cytokini n was added to culture medium, physiologic features such as bud sprouting a nd shoot fresh and dry weight were enhanced. CPPU was also highly efficient for overcoming IBA inhibition of bud outgrowth. Different cultivar respons es were observed.