Potential application of DNA barcoding technology for identification of medicinal plant species traded in Nairobi County, Kenya DNA barcoding for species identification

Abstract

There exists a long history of herbal products use but recently there are concerns on authenticity and safety of some these products. Majority of the herbal products traded in Kenyan markets are processed plant parts, which have been dried or in powder form and are extremely difficult to identify taxonomically. This study was carried out in selected markets in Nairobi County, the capital city of Kenya to assess authenticity of herbal products traded in the region using deoxyribonucleic acid (DNA) barcoding technology by applying internal transcribed spacer (ITS) and ribulose -1,5-bisphosphate carboxylase Large subunit (rbcL) markers. One hundred and twelve herbal products were purchased from practicing herbalists and analyzed using ITS and rbcL DNA barcoding markers. DNA was extracted from acquired samples, amplified and sequences generated. BLAST search with edited generated sequences against the NCBI database was done to recover the expected species. Our findings showed that 35% of the herbal products were wrongly labeled and contained different species compared to those listed on the labels. Out of 92 samples with positive sequences, 58 matched their expected species after the BLAST search. Among the authentic species identified are O. lanceolata, M. oleifera, W. ugandensis, O. europaea, Acacia species, and C. spinarum. However, 32 species did not match the expected species as listed on labels and were concluded to have been substituted. Among them were R. prinoides, T. abyssinica, U. massaica and A. indica, which were substituted with their close relatives, while R. tridentate, Z. usambarense and Prunus africana were substituted with unrelated species with no reported medical benefits. ITS marker had remarkable identification efficiency at 98% to species level compared to rbcL at 89%.  We recommend further studies to establish at what stage substitution takes place, as well as utilization of DNA barcoding technology for medicinal plants authentication and verification