Effect of Medium Physical Support, Shoot Length and Genotype on In Vitro Rooting and Plantlet Morphology of Sweetgum

Adventitious shoots (1 cm and 2 cm long) from 10 clones of sweetgum (Liquidambar styraciflua L.) were rooted on rockwool-supported Woody Plant Medium (WPM) and agar-solidified WPM in vitro. Shoots on rockwool-supported WPM had higher rooting frequency, shoot elongation, and leaf chlorophyll content than those on agar-solidified WPM. The data are consistent with the hypothesis that rockwool supplies more oxygen to the rooting zone. Taller shoots had significantly greater rooting frequency, more shoot elongation, and larger average area per leaf than shorter shoots. Genotype significantly influenced rooting frequency, shoot elongation, average area per leaf, chlorophyll content, and shoot fresh weight. An in vitro auxin pretreatment significantly increased rooting frequency over shoots grown on either agar-solidified or rockwool-supported WPM without auxin.