DNA barcoding of medicinal orchids in Asia

Growing popularity of herbal medicine has increased the demand of medicinal orchids in the global markets leading to their overharvesting from natural habitats for illegal trade. To stop such illegal trade, the correct identification of orchid species from their traded products is a foremost requirement. Different species of medicinal orchids are traded as their dried or fresh parts (tubers, pseudobulbs, stems), which look similar to each other making it almost impossible to identify them merely based on morphological observation. To overcome this problem, DNA barcoding could be an important method for accurate identification of medicinal orchids. Therefore, this research evaluated DNA barcoding of medicinal orchids in Asia where illegal trade of medicinal orchids has long existed. Based on genetic distance, similarity-based and tree-based methods with sampling nearly 7,000 sequences from five single barcodes (ITS, ITS2, matK, rbcL, trnH-psbA and their seven combinations), this study revealed that DNA barcoding is effective for identifying medicinal orchids. Among single locus, ITS performed the best barcode, whereas ITS + matK exhibited the most efficient barcode among multi-loci. A barcode library as a resource for identifying medicinal orchids has been established which contains about 7,000 sequences of 380 species (i.e. 90%) of medicinal orchids in Asia.