Studies on rooting of microshoots of smokebush (
Cotinus coggygria Mill, var. Royal Purple), a woody ornamental, were carried out
in vitro. Microshoots were rooted in a mixed-auxin regime (indole 3-acetic acid, indole butyric acid [IBA], and naphthalene acetic
acid) or singly in the above auxins and the 2,4 dichlorophenoxyacetic acid (2,4-D) over a wide concentration range. Indole
butyric acid at 10 μM proved to be the most suitable treatment, producing less basal callus, 100% rooting, and earlier root
emergence than the other treatments. No roots were formed with 2,4-D. A 6-day root induction period was obtained with 10 μM
of IBA. Histological studies revealed increased mitotic activity after 3 d in culture in the medullary ray cells, which led
to root primordium formation, several of which were formed simultaneously around the base of the explant. The vascular tissues
of these primordia connected to those of the explant, and roots began to emerge from the base by day 10. Thus, direct rhizogenesis
occurred with the IBA treatment, as opposed to the roots that were formed in the basal callus under the mixed-auxin regime.
Keywords Adventitious rooting - Auxin - Direct rhizogenesis - Indole butyric acid - Medullary ray cells - Root primordia
Editor: E. C. Pua