A test of seven candidate barcode regions from the plastome in Picea (Pinaceae)

DNA barcoding, as a tool for species discrimination, has been used efficiently in animals, algae and fungi, but there are still debates on which DNA region(s) can be used as the standard barcode(s) for land plants. Gymnosperms, especially conifers, are important components of forests, and there is an urgent need for them to be identified through DNA barcoding because of their high frequency of collection in the field. However, the feasibility of DNA barcoding in gymnosperms has not been examined based on a dense species sampling. Here we selected seven candidate DNA barcodes from the plastome (matK, rbcL, rpoB, rpoC1, atpF-atpH, psbA-trnH, and psbK-psbI) to evaluate their suitability in Picea (spruce). The results showed that none of them or their different combinations has sufficient resolution for spruce species, although matK+rbcL might be used as a two-locus barcode. The low efficiency of these candidate barcodes in Picea might be caused by the paternal inheritance of the chloroplast genome, long generation time, recent radiation, and frequent inter-specific hybridization aided by wind pollination. Some of these factors could also be responsible for the difficulties in barcoding other plant groups. Furthermore, the potential of the nuclear LEAFY gene as a land plant barcode was discussed.