Effect of IBA Concentration, Carbon Source, Substrate, and Light Source on Root Induction Ability of Tree Peony (Paeonia suffruticosa Andr.) Plantlets in Vitro

Summary Rooting in tree peony (Paeonia suffruticosa Andr.) remains the most difficult challenge in the tissue culture of this woody ornamental plant. In a bid to increase rooting ability of tree peony plants in vitro, several abiotic factors were assessed. Indole-3-butyric acid (IBA) concentration, carbon source, substrate, and light source affected the root induction ability of tree peony cv. ‘Wu Long Peng Sheng’. Without IBA, no roots formed. At 4 mg l–1 IBA, all rooting parameters were highest. When plantlets were cultured under lightemitting diodes (LEDs) or cold cathode fluorescent lamps (CCFLs) on rooting medium, rooting percentage on rockwool was higher than on Gellan gum. However, rooting percentage was higher under heat fluorescent lamps than under LEDs or CCFLs, independent of the medium substrate. Sucrose resulted in higher rooting ability than CO2-enrichment under any light source; moreover, CO2-enrichment appeared to have a detrimental effect on rooting percentage. Rooting was better under heterotrophic than under photoautotrophic conditions. Rooting of tree peony was successfully achieved under various conditions, which will greatly benefit the micropropagation of this difficultto-root tree.