Micropropagation with a novel pattern of adventitious rooting in American sweetgum (Liquidambar styraciflua L.)

Liquidambar styraciflua L. has great potential not only as an ornamental, but also for its commercial importance in pulp and paper production or biomass energy. This study was designed to evaluate the influence of plant growth regulators on adventitious shoot multiplication from shoot tips, and in vitro adventitious rooting. The morphogenic capacity of intact leaves grown in vitro was also assayed for adventitious shoot formation and aerial root development. The highest shoot multiplication rate of 5.9 shoots per explant was achieved with 0.7 mg l−1 6-benzylaminopurine plus 0.01 mg l−1 indole-3-butyric acid. Thidiazuron, alone or in combination with 6-benzylaminopurine, did not significantly support higher shoot multiplication rates. The organogenic ability of the in vitro grown leaves was significantly lower and slower in comparison with shoot tips. Microshoots rooted readily after transfer to a half-strength woody plant medium supplemented with 0.5–0.7 mg l−1 1-naphthaleneacetic acid, and were then successfully acclimatised to an ex vitro environment. A novel pattern of adventitious rooting was observed from the aerial parts of microshoots which were not in contact with the medium, including the parenchyma cells of the leaf blades as well as stem nodes and internodes. The regenerated plants established in soil did not show any detectable morphological variation.