In vitro propagation of Acacia mangium and A. mangium × A. auriculiformis.

Acacia mangium and A. mangium × A. auriculiformis hybrids have gained an increasing interest in reafforestation programs under the humid tropical conditions, mainly for pulpwood production. This is due to their impressive growth on acid and degraded soils, as well as their capability to restore soil fertility thanks to their natural nitrogen-fixing ability. It is crucial to develop efficient methods for improving the genetic quality and the mass production of the planting stocks of these species. In this regard, in vitro micropropagation is well suited to overcome the limitations of more conventional techniques for mass propagating vegetatively selected juvenile, mature, or even transgenic genotypes. Micropropagation of A. mangium either from seeds or from explants collected from outdoors is initiated on Murashige and Skoog (MS) basal medium supplemented with 4.4 µM BA. Microshoot cultures produced by axillary budding are further developed and maintained by regular subcultures every 60 days onto fresh MS culture medium added with 2.2 µM BA + 0.1 µM NAA. This procedure enhances the organogenic capacity for shoot multiplication by axillary budding, with average multiplication rates of 3-5 every 2 months, as well as for adventitious rooting. The rooting is initiated on Schenk and Hildebrandt culture medium containing 4 µM IAA. The maintenance of shoot cultures in total darkness for 3 weeks increases the rooting rates reaching more than 70%. The hybrid A. mangium × A. auriculiformis genotypes are subcultured at 2-month intervals with an average multiplication rate of 3 and rooting rates of 95-100% on a half-strength MS basal medium containing 1.1 µM NAA. The rooted microshoots are transferred to ex vitro controlled conditions for acclimatization and further growth, prior to transfer to the field, or use as stock plants for cost-effective and true-to-type mass production by rooted cuttings.