DNA barcoding is becoming more and more important for rapid and accurate identification of plant species. After a joint international effort, the two-marker combination of rbcL+matK was proposed as the ‘core’ barcode for land plants in August 2009 by CBOL Plant Working Group 2009, and trnH-psbA and ITS suggested as supplementary barcodes. To evaluate the universally and effectiveness of the four candidate barcodes (i.e. rbcL, matK, trnH-psbA and ITS), a coordinated effort has been made to further evaluate the markers, as a response to the call of the Third International Barcoding of Life Conference in 2009.
A large data set, involving 6286 individuals representing 1757 species in 141 genera of 75 families of seed plants, was pooled by the China Plant BOL Group. Comprehensive analysis of the dataset was made to assess the universality, sequence quality and discriminatory power of the markers. The results indicated that the three chloroplast markers showed higher level of universality, while ITS performed moderately well in angiosperms, but not so in gymnosperms. As to the discriminatory power, ITS provided the highest among the four markers, and a combination of ITS with any chloroplast DNA marker could improve species discrimination significantly with 69.9-79.1% discriminatiory power, which was significat higher than that of rbcL+matK with 49.7%. In additon, the ITS2 alos showed relatively high discriminatiory power. Baed on a compresive evaluation, ITS (or ITS2) together with rbcL, matK should be incorporated into the core barcode for seed plants.
This results have been reported in Proceedings of the National Academy of Sciences of the United States of America (PNAS) (2011, 108: 19641–19646). http://www.pnas.org/content/108/49/19641
Discrimination success at the ordinal level (1 order of gymnosperms, 23 orders of angiosperms) for four markers (plus ITS2, the ITS partial sequence) and all possible 2- to 4-marker combinations, based on 3,011 individuals representing 765 species, where at least 2 species were sampled per genus and all four markers were successfully sequenced (I, ITS; I2, ITS2; M, matK; P, trnH–psbA; R, rbcL). Sequence of angiosperm orders is according to the Angiosperm Phylogeny Group (APG) III (42). (image by China Plant BOL Group)
