In Vitro Induction of Polyploidy by Colchicine in the Protocorm of the Orchid Dendrobium wardianum Warner

Dendrobium wardianum is a key ornamental plant and a valuable traditional Chinese medicine. This research aimed to find the optimal protocol for in vitro inducement of polyploidy in D. wardianum by treating protocorms with colchicine (an antimitotic agent). The experiment consisted of two series of treatments. For the first treatment, the protocorms were subjected to colchicine concentrations of 25, 75, 125, 250, and 500 μM (weight/volume) for 6, 12, and 24 hours. For the second treatment, protocorms were cultivated in culture medium with colchicine (25, 75, 125, and 250 μM) for 30 days. A total of 18 polyploids were confirmed by chromosome counts and anatomical parameters. Polyploids had broad, dark green leaves with increased stem lengths compared with those of diploids. The optimal protocol for these two methods consisted of soaking in 250 μM of colchicine solution for 12 hours, resulting in inductivity of 26%, and cultivating in 75 μM for 30 days, resulting in a mutation rate of 34%. A comparison of these two protocols showed that the latter one induced more stable polyploids, but that the survival rate was slightly lower. The survival and induced mutation rates of these plants were significantly influenced by the colchicine concentration and exposure time. Higher concentrations for longer periods of time resulted in greater mortality rates and longer-lasting side effects. The protocol involving a solid medium and colchicine is worth considering. It will be intriguing to examine this methodology for the induction of stable polyploids of other orchid species.