Vegetative propagation of Acacia mangium Wild. by stem cuttings and tissue culture techniques
The main objectives of this investigation were: 1. to evaluate vegetative propagation of Acacia mangium using stem cuttings and tissue cultures techniques as a means of producing healthy planting stock, 2. to study the anatomy of root formation and development in Acacia mangium stem cuttings, and 3. to study the physiological and morphological factors involved in rooting of Acacia mangium stem cuttings.Acacia mangium stem cuttings rooted easily but the rooting percentage declined with the increasing age of stock plants. The application of auxins and the use of cuttings with half size phyllodes increased the rooting percentage. A 1:1 mixture of sand and Irish sphagnum peat was found to be the best rooting medium. The anatomical studies of a 1-year-old stem showed that the Acacia mangium stem did not have preformed root premordia but the root primordia were initiated in the phloem region, very near to cambial cells, in between the active medullary rays. A micropropagation technique for Acacia mangium was successfully developed. The optimum cytokinin concentration for multiple shoot induction was found to be 0.5 mg/1 of BAP for nodal explants from aseptically germinated seedlings and 1.0 mg/1 of BAP for nodal explants of 8-month-old greenhouse-grown seedlings, giving an average of 25.6 and 16.9 shoots per explant respectively. Shoots which were ≥0.5 cm in length were easily rooted in a humidified rooting chamber. It is estimated that after six culture cycles each of 2 months duration, more than 87 million rooted shoots could be obtained from a single aseptically germinated seedling and more than 1 million rooted shoots could be obtained from a single nodal explant of 8-month-old greenhouse-grown seedlings. A healthy callus was readily obtained from stem explants of 1-month-old aseptically germinated seedlings but all attempts to induce shoots from callus failed.