| Summary: | <p>Abstract</p> <p>Background</p> <p>Based on the testing of several loci, predominantly against floristic backgrounds, individual or different combinations of loci have been suggested as possible universal DNA barcodes for plants. The present investigation was undertaken to check the applicability of the recommended locus/loci for congeneric species with <it>Dendrobium </it>species as an illustrative example.</p> <p>Results</p> <p>Six loci, <it>matK, rbcL, rpoB, rpoC1, trnH-psbA </it>spacer from the chloroplast genome and ITS, from the nuclear genome, were compared for their amplification, sequencing and species discrimination success rates among multiple accessions of 36 <it>Dendrobium </it>species. The <it>trnH-psbA </it>spacer could not be considered for analysis as good quality sequences were not obtained with its forward primer. Among the tested loci, ITS, recommended by some as a possible barcode for plants, provided 100% species identification. Another locus, <it>matK</it>, also recommended as a universal barcode for plants, resolved 80.56% species. ITS remained the best even when sequences of investigated loci of additional <it>Dendrobium </it>species available on the NCBI GenBank (93, 33, 20, 18 and 17 of ITS, <it>matK, rbcL, rpoB </it>and <it>rpoC1</it>, respectively) were also considered for calculating the percent species resolution capabilities. The species discrimination of various combinations of the loci was also compared based on the 36 investigated species and additional 16 for which sequences of all the five loci were available on GenBank. Two-locus combination of <it>matK+rbcL </it>recommended by the Plant Working Group of Consortium for Barcoding of Life (CBOL) could discriminate 86.11% of 36 species. The species discriminating ability of this barcode was reduced to 80.77% when additional sequences available on NCBI were included in the analysis. Among the recommended combinations, the barcode based on three loci - <it>matK, rpoB </it>and <it>rpoC1</it>- resolved maximum number of species.</p> <p>Conclusions</p> <p>Any recommended barcode based on the loci tested so far, is not likely to provide 100% species identification across the plant kingdom and thus is not likely to act as a universal barcode. It appears that barcodes, if based on single or limited locus(i), would be taxa specific as is exemplified by the success of ITS among <it>Dendrobium </it>species, though it may not be suitable for other plants because of the problems that are discussed.</p>
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