Influence of auxins and darkness on in vitro rooting of micropropagated shoots from mature and juvenile Acacia mangium

The influence of total darkness versus a 16/8 photoperiod and of auxins added to the culture medium on the in vitro root formation capacity of Acacia mangium microshoots of juvenile and mature origin was examined. Rooting of the mature clone was significantly increased by exposing the microshoots to auxins (4 and 6 μM IAA or IBA) in darkness, while the promoting effect of darkness combined with 4 μM IAA was more time-restricted for the juvenile-origin microshoots. Overall, the latter rooted in greater proportions than those from the mature source. Maintaining the microshoots of both origins on auxin supplemented medium in darkness resulted in a greater number of adventitious roots formed than under the standard 16/8 lighting conditions. On the other hand, light stimulated root elongation. These results are discussed mainly from the viewpoint of auxin metabolism in relation to adventitious root formation.