Evaluation of the plastid and nuclear DNA barcodes in genus Ocimum towards quality assurance in herbal industry

Rationale Species of the genus Ocimum are of immense value and are in high demand in trade which leads to unscrupulous adulteration of both crude drugs as well as formulations. Traditional method-based authentication is difficult in case of incomplete or damaged samples and in dried herbal bulk material. High degree of morphological similarity, issues of polyploidy, and the possibility of inter- and intraspecific hybridization have plagued the Ocimum market. Hence, there is an immediate need for developing DNA barcodes for fast and accurate identification of the species. Objective In this study, three plastid regions (matK, rbcL, and trnH-psbA) and two nuclear regions (ITS and ITS2) have been evaluated for their performance as DNA barcodes to check the delineation of Ocimum species. Materials and Methods Five widely accepted markers were assessed for their efficiency using methods like Nearest genetic distance, Wilcoxon test, Best Match (BM), and Neighbor-Joining (NJ) tree methods. Conclusion Our study suggests that discrimination rate amongst single barcodes is the highest for trnH-psbA with the NJ analysis (92 %). By combining two or more barcodes, no significant changes were observed. A reliable and commercially viable DNA barcoding system has been developed for accurate species identification of various Ocimum species. The varied approaches used in the investigation had different species identification potential. The identification success rates of plastid DNA and nuclear DNA barcodes were comparable using pairwise genetic distance (PWG-distance), BM, and NJ methods. Despite having high inter-specific and the lowest intra-specific genetic distance, trnH-psbA failed to discriminate Ocimum species having hybrid origin, indicating the need to develop more suitable barcode loci in future.