DNA barcodes for discriminating the medicinal plant Isatis indigotica Fort. (Cruciferae) and its adulterants

Isatis indigotica Fort. (Cruciferae) is a biennial medicinal plant. In order to protect the decreasing natural genetic resources of I. indigotica, three candidate DNA barcodes (ITS2, trnL-F and rbcL) were employed to establish an accurate and effective identification system for I. indigotica. The results demonstrated that all three candidate DNA barcodes have performed very well in I. indigotica. The interspecific genetic distances were obviously greater than the intraspecific distance among I. indigotica as indicated by ITS2, trnL-F and rbcL. Sequence alignment analysis of I. indigotica genotypes revealed that four SNPs (54, 108, 146 and 181 bp) located in ITS2, three (2, 30, 709 bp) in trnL-F and one (531 bp) in rbcL, respectively. UPGMA phylogenetic tree constructed from trnL-F and rbcL could allote I. indigotica to the correct corresponding genus, whereas rbcL could not distinguish I. indigotica from its adulterants. Meanwhile, UPGMA tree of ITS2 could accurately identify I. indigotica from its adulterants according to the corresponding species. Consequently, it can be concluded that ITS2 is a more suitable and accurate DNA barcode for identifying I. Indigotica and its adulterants than trnL-F and rbcL.