Abstract: Many types of Cymbidium have high ornamental and economic value and occupy important position in the orchid industry. However, due to the complex evolution and genetic history of Cymbidium, there have been problems in identification and there are many taxonomic disputes. In recent years, the rapid development of DNA barcoding technology has provided new ideas for taxonomy and molecular identification. In this study, 12 native samples of Cymbidium and 250 Orchidaceae ITS2 sequences downloaded from GenBank (81 of which belong to the genus Cymbidium) were used to evaluate the feasibility of ITS2 sequence for molecular identification of Cymbidium by BLAST1, genetic variation, and phylogenetic tree-construction methods, and based on the results of phylogenetic tree-construction, explored the phylogenetic relationship of the genus Cymbidium. The results of BLAST1 showed that ITS2 sequence could accurately identify the genus and subgenus of 12 native Cymbidium samples, and the success rate of identification was 100%. It also had good identification ability at the section level, the success rate was 92%. But at the species level, identification ability was poor, and the identification success rate was only 17%. The genetic variation analysis of the reference library (250 ITS2 sequences of Orchidaceae downloaded from GenBank) showed that the Cymbidium ITS2 sequences had high genetic diversity (variation rate was 74.9%), and could be better distinguished at the genus and subgenus levels, but the level of species under the section or section were poor due to the large overlap between intra-and inter-section variation, intra-and inter-species variation. According to the analysis of phylogenetic tree, ITS2 sequence could clearly distinguished subgenus Jensoa, Cymbidium and Cyperorchis. The relationship between the subgenus Jensoa and Cymbidium was relatively close, and they were both far from the subgenus Cyperorchis. At the same time, it was also found that Cymbidium tortisepalum and C. goeringii were close in the phylogenetic tree. This result supported the division of the 3 subgenus of Du Puy & Cribb, and suggested that C. tortisepalum might be a variety or variety from C. goeringii(bootsrap value was 69%). In summary, ITS2 sequences had certain application value in the molecular identification of Cymbidium, and could be used as an auxiliary sequence for the DNA barcoding identification of Cymbidium.

Key words: ITS2, Cymbidium, DNA barcoding, phylogenetic relationship, Orchidaceae