Plant Regeneration of Hybrid Poplars Using Nodule Culture System
Development of micropropagation method for hybrid poplars, Populus euramericana, P. nigra X P. maximowiczii, was established using nodule culture system. Callus was initiated from in vitro cultured leaf expiants of hybrid poplars on Murashige and Skoog’s medium supplemented sucrose 20 mg/l, agar 7 g/l, and 2,4-D 0.5 mg/1. To raise cell suspension, the induced calli from leaf expiant cultures were transferred to liquid medium of the same composition. Among 4 tested BA concentrations, BA 0.2 mg/1 gave the best formation of fine nodules (about l-2mm diameter) after 2 weeks of culture. Using the developed liquid nodule culture system, the fine nodules grow via nodule enlargement (about 5–7mm diameter) and nodule multiplication. Plant regeneration could be obtained from the nodule (3–5mm diameter) in liquid medium or on agar solidified medium. In parti-cular, the regeneration medium with BA 0.5 mg/1 and adenine sulfate 40 mg/1 stimulated shoot differentiation on hybrid poplar nodules.