DNA barcoding in closely related species： A case study of Primula L. sect. Proliferae Pax （Primulaceae） in China

DNA barcoding is a method of identifying species by analyzing one or a few short standardized DNA sequences. There are particular challenges in barcoding plants, especially for distinguishing closely related species. Hence, there is an urgent need to evaluate the performance of candidate loci for distinguishing between species, especially closely related species, to complement the rbcL ＋ matK combination suggested as the core barcode for land plants. We sampled 48 individuals representing 12 species in Primula sect. Proliferae Pax in China to evaluate the performance of eight leading candidate barcode loci （matK, rbcL, rpoB, rpoC1, trnH-psb.4, psbK-psbI, atpF- atpH, and internal transcribed spacer （ITS））. The core combination rbcL ＋ matK gave only 50% species resolution in sect. Proliferae. In terms ofintraspecies and interspecies divergence, degree of monophyly, and sequence similarity, ITS, trnH-psbA, and psbK-psbI showed good performance as single-locus barcodes. Internal transcribed spacer displayed the highest genetic divergence and best discriminatory power, both alone and in combination with rbcL ＋ matK （83.3% species resolution）. We recommend evaluating the use of ITS for barcoding in other species. Low or single copy nuclear regions would provide more sophisticated barcoding tools in the long term, even though further research is required to find suitable loci.