Abstract: The polyploid breeding technique was used to induce polyploid of Dendrobium devonianum, an orchid occurring in the tropics of Yunnan with ornamental and medicinal values . The materials for polyploid breeding were in vitro seedlings of diploids . The polyploid plants could be induced in a short time with colchicines as mutagen . It resulted in the best inductive effect to use 0 . 03% colchicines to deal with the in vitro seedlings of diploids for 24 hours . The polyploid plants were different from those of diploids in morphology , stoma diameter , chromosome numbers, and DNA fingerprints . The in vitro seedlings of polyploid plant showed advantageous characteristics such as thicker stems and leaves . It is a successful case to apply polyploid breeding technique into the tropical orchid breeding in China .

Key words: Dendrobium devonianum