Micropropagation and in vitro flowering of Dendrobium wangliangii: A critically endangered medicinal orchid

Dendrobium wangliangii is seriously threatened because of anthropogenic and environmental pressures. A protocol with seed asymbiotic germination was developed to conserve the orchid in vitro. The germination rate was 92% under 16/8 h (light/dark) photoperiod after 240 days from hand-pollination in a modified medium. Polyembryony was founded in D. wangliangii, with a percentage of 0.87%. Half MS promoted the protocorms proliferation well, with the protocorms differentiated at the frequency of 28.79% when cultured on half MS, supplemented with 2 mg L-1 6-benzylaminopurine (BA) and 0.1 mg L-1naphthaleneacetic acid (NAA). Additives, especially 100 ml L-1 coconut milk (CM), improved the protocorm differentiation greatly but led to a lethality of 49.92%. The pretreatment of 1 mg L-1 GA3 for 15 days, after inoculated to the medium amended with 2 mg L-1 BA, 0.1 mg L-1 NAA and 100 ml L-1 CM, increased the differentiation to 54.68%. The combination of 2 mg L-1 BA, 0.1 mg L-1 NAA, and 100 ml L-1 CM also showed an efficient role in adventitious bud multiplication. CM effectively controlled the albino phenotype. In addition, inflorescence induction (100%) was produced with 2 mg L-1 1-phenyl-3-(1, 2, 3-thiadiazol-5-yl)-urea (TDZ) and the best flower development was obtained with 0.3 mg L-1 paclobutrazol (PP333), and 0.5 mg L-1 NAA.   Key words: Dendrobium wangliangii, micropropogation, asymbiotic germination, adventitious buds multiplication, polyembryony, in vitro flowering.