Evaluation of the capacity of the DNA barcode ITS2 for identifying and discriminating dryland plants
Many of the plants that grow in arid and semi-arid regions under harsh conditions (drought, salinity and misuse) are of medical importance. Desert plants also provide other benefits; so conservation efforts should be strengthened in these areas. In this study, three DNA barcodes – chloroplast maturase-K (matK), ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) and secondary internal transcribed spacer (ITS2) – were tested in order to determine the ability of these markers to distinguish between various species. A total of 93 fresh and dry samples belonging to 30 plant families were examined. These are native to the arid lands around Makkah in the Kingdom of Saudi Arabia. Various tools and tests were used to evaluate the efficiency of the barcode markers; these included the basic local alignment search tool (BLAST), as well as the use of inter- and intraspecific distances, barcode gap, prediction of the secondary structure of the ITS2 and phylogenetic methods. The results confirmed the efficiency and superiority of the ITS2 loci over two chloroplast genes: matK and rbcL. ITS2 had a 97% success rate with amplification and a 95% success rate with sequencing, showing 100% identification at the family level, 77% identification at the genus level and 70% species resolution. A clear barcode gap was observed between inter- and intraspecific distances. Identification was achieved even in cases of degraded samples or old herbarium specimens. This study contributes to DNA barcode data by adding 224 DNA sequences of desert plants to the National Center for Biotechnology Information NCBI database. The results of this study are important and useful for application in each of the following fields: validation of medicinal plant identity, conservation, and taxonomic and evolutionary studies.