In vitro Propagation of Araucaria cunninghamii and Other Species of the Araucariaceae Via Axillary Meristems

Abstract

Stem segments with 3-5 leaf axils, excised from the upper portion of the mainstem of 2-year-old hoop pine (Araucaria cunninghamii Aiton ex D. Don) seedlings, produced orthotropic buds from the concealed axillary meristems when cultured on a basal medium (BM) of half-strength Murashige and Skoog (MS) inorganic salts, the medium level of growth factors and amino acids of de Fossard, 20 g L sucrose and 6.5 g/L agar. This procedure was also successful with A. balansae, A. bidwillii, A. colurnnaris, A. hunsteinri, A. luxurians, A. montana, A. rulei, A. scopulorum and Agathis robusta and with stem segments from orthotropic coppice shoots of juvenile morphology collected from the stumps of 20-year old hoop pines felled near ground level. The hoop pine explants were highly sensitive to cytokinin; 1 μM and 10 μM 6-benzylaminopurine caused the formation of distorted buds and total inhibition of bud development respectively. Lofier concentrations (0.001-0.1 μM ) did not noticeably influence bud formation or development. A low rate of multiplication was induced by reculturing the stem segments after the excision of the initial shoots. New buds developed in the leaf axils of that part of the initial shoot which remained attached to the primary stem explant. Shoots derived from seedling and coppice cultures of hoop pine and seedling cultures of Agathis robusta rooted in vitro on BM + 0.1-10.0 μM indole-3-butyric acid (IBA), but with only 5-20% success. Up to 80% rooting was obtained if both hoop pine shoot types (i. e. from seedling and coppice cultures) were cultured on modified BM (quarter strength MS salts, 10 μM IBA plus no agar) for 2 weeks, before being transferred to a mixture of non-sterile peat and perlite or vermiculite and perlite, maintained under a high humidity (90-95%). Plantlets were subsequently transferred to normal glasshouse conditions and then to the field with less than 5% mortality. Thus hoop pine can be added to the relatively small number of conifers for which the capacity to micropropagate juvenile and mature plants and successfully establish their clones in the field has been demonstrated.