Growth Regulators Influence Root and Shoot Development of Micropropagated Algerian Ivy

Shoots of greenhouse-grown Algerian ivy (Hedera canariensis L.) were surface disinfected and explanted on modified Murashige and Skoog (MS) medium supplemented with BA (10 μM) and NAA (2.5 μM). One month later the shoots were transferred to MS proliferation medium supplemented with TDZ (0.1 or 0.5 μM) and NAA (40 μM). An average of three microshoots developed on each stem treated with TDZ. Pruned shoots grown on MS medium supplemented with GA3 (20 μM) and BA (20 μM) branched better than unpruned shoots (3.7 vs. 1 per explant, respectively). Rooted shoots grown ex vitro grew and developed a shape suitable for commercial sale in 3 months. Chemical names used: N -(phenyl-methyl)-l H -purine-6-amine (BA); gibberellic acid (GA3); 1-naphthaleneacetic acid (NM); N -phenyl-W-1,2,3-thiadiazo-5-yl urea (Thidiazuron, TDZ). Table 1. Effects of combinations of NAA and TDZ on root and shoot growth characteristics and on callus formation of Algerian ivy microshoots grown in vitro and evaluated 4 weeks after explanting. z Algerian ivy, a popular woody ornamental species, is used as a hanging basket plant or as a groundcover in warm climates. It displays strong apical dominance and does not readily branch even after pruning. Improved production methods that increase branching would reduce the time required to produce a saleable crop. Anderson (1975) reported that tissue culture-produced rhododendrons have a more compact habit and more branches. One method to accelerate the production of Algerian ivy could be through micropropagation in vitro. There have been two reports of Algerian ivy being cultured in vitro (Shantz and Steward, 1959; Stoutemyer and Britt, 1965); both involved callus cultures, and shoot formation was not reported. In contrast, a related species, English ivy (Hedera helix L.), has been studied extensively in vitro; the majority of this literature examines callus cultures and the role of juvenility and maturity in root development (Geneve et al., 1988, 1990; Hackett, 1988). Sporadic somatic embryogenesis and adventitious bud formation have been reported for English ivy callus (Banks, 1979; Banks et al., 1979). Therefore, this Received for publication 29 Oct. 1990. This research was supported in part by the Univ. of Illinois Agricultural Experiment Station (project: RRF Ht S103 0352) and the Iraqi government. Thanks to Nor-Am Chemical Co. for supplying samples of Thidiazuron. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1Lecturer, Univ. of Baghdad, Iraq. 2Professor. HORTSCIENCE, VOL. 26(8), AUGUST 1991 study was initiated to develop an in vitro technique to propagate Algerian ivy. Stem cuttings (eight to 10 nodes) of greenhouse-grown juvenile phase Algerian ivy were divided into one-node explants. The explants were washed for 1 min in a 0.1 w/v Alconox solution, rinsed with sterile distilled water (SDW), soaked for 5 sec in 70% ethanol, rinsed with SDW, and soaked for 15 min in a 0.5% NaOCl solution containing 0.1% (v/ v) Tween 20. Nodal segments were then rinsed three times (5 min each) with SDW Media with NAA or IBA and shoot growth (Expt. 1). Single node microshoots were excised from whole explants growing in vitro and moved either to full MS or half-strength MS salts (one-half MS) containing either auxin (NAA) or 1 H -indole-3-butyric acid (IBA) at seven concentrations (0, 2.5, 5, 7.5, 10, 20, or 30 μM). A single microshoot (experiment unit) was placed into a 150 × 25-mm culture tube containing 15 ml of medium. A completely randomized experimental design with 24 single microshoot replicates per treatment was used. Cultures were evaluated for number of shoots produced by the single axillary bud per explant. Media with NAA and TDZ and growth characteristics (Expt. 2). MS media containing 5 × 3 factorial combinations of NAA (0, 10, 20, 30, or 40 μM) and TDZ (0, 0.1, or 0.5 μM) were dispensed 50 ml/vessel into 350-ml propylene GA7 (Magenta Corp., Chicago) vessels randomly arranged in culture racks. Terminal microshoots (1 to 2 cm long) were taken from stock cultures and placed one in each culture vessel. There were and aseptically separated into 1.5to 2.0-cm sections, each containing one bud. All explants were placed on a modified (MS) medium (Murashige and Skoog, 1962) supplemented with 10 μM BA, 2.5 μM NM, and (in mg·liter) 0.5 thiamine HCI, 1 pyridoxine, 5 nicotinic acid, 2 glycine, 100 myoinositol, and 30 g sucrose/liter. Before autoclaving, gentamicin sulfate at 3 mg·liter was added to suppress bacterial growth. The pH was adjusted to 5.6 to 5.7 and agar (7 g-liter-l) was added. The medium was autoclaved at 106 kPa pressure at 120C for 15 min. All cultures were grown at 22 to 24C under cool-white fluorescent lights (40 to 60 μmol m ·s) with a 16-h photoperiod. All the explants were maintained for 1 month on MS medium.