Growth Hormones and Propagation of Cymbidium in vitro

Abstract Protocorms of Cymbidium (Orchidaceae) were grown on solid or liquid medium with macro‐nutrients according to Wimber (van Raalte 1967) and iron, micro‐nutrients and vitamins according to Nitsch (1968) the medium also contained 2% sucrose. The effects of 1) the auxins; indol‐3yl‐acetic acid (IAA), α‐naphthaleneacetic acid (NAA) and 2,4‐dichlorophenoxyacetic acid (2,4‐D); 2) the cytokinins; 6‐furfurylaminopurine (kinetin) and benzyladenine (BA) and 3) the gibberellin; gibberellic acid (GA) were examined alone or in combinations. IAA had no effect alone. NAA resulted in optimal fresh weight at 10 μM and the protocorms were vigorous, but lighter green than usual. 2,4‐D caused a high weight increase at 1 μM, but the protocorms were abnormal. Higher concentrations of NAA and 2,4‐D inhibited chlorophyll synthesis. On solid medium kinetin (100 μM) induced a growth of many small shoots, but had no effect on the fresh weight. In liquid medium, kinetin promoted a callus formation and fresh weight increase. BA had effects similar to kinetin, but at lower concentrations. GA alone promoted shoot and leaf growth. Combinations of kinetin and NAA resulted in a maximal fresh weight increase at kinetin concentrations one tenth of the NAA concentrations. The optimal growth and the best development occurred at 10 μM NAA and 1 μM kinetin. NAA and kinetin together could limit the shoot and leaf growth induced by GA.