In vitro rooting of juvenile and mature<Emphasis Type="Italic"> Acacia mangium</Emphasis> microcuttings with reference to leaf morphology as a phase change marker

Rooting capacity of microshoots derived from a mature clone of Acacia mangium Willd. and from its juvenile progeny was compared in different in vitro conditions and in relation to leaf morphology as a phase change marker. Rooting capacity of the mature clone appeared to depend a lot on rooting medium composition, in contrast to the juvenile plant material. On a SH/3 derived medium with 4 µM IAA, the rooting rates varied significantly according to microshoot morphology and light regime starting from day 14. Maintaining the microshoots for 3 weeks in total darkness prior to transfer to the standard 16-h photoperiod increased the rooting rates overall. Mature-like microshoots of juvenile origin rooted in much lower proportions than the juvenile-like ones under the 16-h photoperiod, whereas no difference in rooting rates between the two morphological types was observed after 3 weeks in total darkness. The results were totally opposite for the mature clone for which 3 weeks in darkness, in contrast to the 16-h photoperiod, induced morphology-related differences in rooting rates with higher scores for the juvenile type. This study shows that under certain conditions, A. mangium microshoots from mature origin but with juvenile morphology can root in vitro with similar success rates (70%) to microshoots from juvenile plant material. However, the inconsistencies observed between the two age classes of microshoots in relation to photoperiod refute the use of foliar morphology as a reliable marker of rooting ability in A. mangium, although these two traits are classically referred to as phase change indicators.