Micropropagation of Metrosideros excelsa

Multiple shoots were induced on stem segments of an 8-y-old plant of Metrosideros excelsa Sol ex Gaertn. Parnel. Axillary shoots produced on uncontaminated explants were excised, segmented, and recultured in the same medium to increase the stock of shoot cultures. The Murashige and Skoog (MS) medium, augmented with different concentrations of 2- isopenthenyladenine (2iP) and indole-3-acetic acid (IAA), either singly or in combinations, as potential medium for shoot multiplication by nodal segments was tested. In the following experiment, equal molar concentrations of four cytokinins [2iP, kinetin, zeatin, and N-6-benzyladenine (BA)] in combination with equal molar concentrations of three auxins [IAA, alpha-naphthaleneacetic acid (NAA), and indole-3-butyric acid (IBA)] were tested for ability to induce axillary shoot development from single-node stem segments. The highest rate of axillary shoot proliferation was induced on MS agar medium supplemented with 1.96 mu M 2iP and 1.14 mu M IAA after 6 wk in culture. Different auxins (IAA, IBA, and NAA) were tested to determine the optimum conditions for in vitro rooting of microshoots. The best results were accomplished with IAA at 5.71 mu M (89% rooting) and with IBA at 2.85 or 5.71 mu M (86% and 86% rooting, respectively). Seventy and 90 percent of the microshoots were rooted ex vitro in bottom-heated bench (22 +/- 2 degrees C) after 2 and 4 wk, respectively. In vitro and ex vitro rooted plantlets were successfully established in soil.