IN-VITRO SHOOT APEX MICROGRAFTING OF MATURE ACACIA-MANGIUM

Prospects for in vitro micrografting shoot apices of mature Acacia man gium trees were investigated with the use of 432 micrografts. Overall success rates of 51.5% were obtained for shoot apices ranging from 200 to 400 mu m in length, and a short basal wedge of underlying tissues top-grafted in aseptic conditions onto 2-to-3-month-old in vitro grown Acacia mangium seedlings. The successfully established micrografts di splayed, however, substantial variability in terms of further scion el ongation as 41% of these micrografts, or 21.2% only of the total amoun t of the micrografts performed, had resumed growth two months after mi crografting. The elongated scions exhibited different types of morphol ogy, ranging from juvenile-like type composed leaves to the predominan t mature-like phyllode morphology. Side-grafting, a more difficult pro cedure to perform than top-grafting, or placing the micrografts for 2 weeks in darkness after grafting, did not improve the scores. Moreover , attempts to micrograft meristems (150-200 mu m) resulted in 5% succe ss only.