In vitro rooting of microshoots of Cotinus coggygria Mill, a woody ornamental plant

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.