title: Barcoding poplars (Populus L.) from western China.
abstract: BACKGROUND
  Populus is an ecologically and economically important genus of trees, but distinguishing between wild species is relatively difficult due to extensive interspecific hybridization and introgression, and the high level of intraspecific morphological variation. The DNA barcoding approach is a potential solution to this problem.
  
  
  RESULTS
  Here, we tested the discrimination power of five chloroplast barcodes and one nuclear barcode (ITS) among 95 trees that represent 21 Populus species from western China. Among all single barcode candidates, the discrimination power is highest for the nuclear ITS, progressively lower for chloroplast barcodes matK (M), trnG-psbK (G) and psbK-psbI (P), and trnH-psbA (H) and rbcL (R); the discrimination efficiency of the nuclear ITS (I) is also higher than any two-, three-, or even the five-locus combination of chloroplast barcodes. Among the five combinations of a single chloroplast barcode plus the nuclear ITS, H+I and P+I differentiated the highest and lowest portion of species, respectively. The highest discrimination rate for the barcodes or barcode combinations examined here is 55.0% (H+I), and usually discrimination failures occurred among species from sympatric or parapatric areas.
  
  
  CONCLUSIONS
  In this case study, we showed that when discriminating Populus species from western China, the nuclear ITS region represents a more promising barcode than any maternally inherited chloroplast region or combination of chloroplast regions. Meanwhile, combining the ITS region with chloroplast regions may improve the barcoding success rate and assist in detecting recent interspecific hybridizations. Failure to discriminate among several groups of Populus species from sympatric or parapatric areas may have been the result of incomplete lineage sorting, frequent interspecific hybridizations and introgressions. We agree with a previous proposal for constructing a tiered barcoding system in plants, especially for taxonomic groups that have complex evolutionary histories (e.g. Populus).
authors: School of Earth and Environmental Sciences & State Key Laboratory of Grassland Agro-Ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China ; College of Plant Sciences, Xinjiang Production & Construction Corps Key Laboratory of Protection and Utilization of Biological Resources in Tarim Basin, Tarimu University, Alar, Xinjiang, People's Republic of China.
authors: Jianju
authors: J
authors: Feng
authors: Dechun
authors: D
authors: Jiang
authors: Huiying
authors: H
authors: Shang
authors: Miao
authors: M
authors: Dong
authors: Gaini
authors: G
authors: Wang
authors: Xinyu
authors: X
authors: He
authors: Changming
authors: C
authors: Zhao
authors: Kangshan
authors: K
authors: Mao
mesh_terms: D002681:China; D058893:DNA Barcoding, Taxonomic / Q000379:methods*; D018744:DNA, Plant / Q000235:genetics; D056426:Genetic Loci / Q000235:genetics; D014644:Genetic Variation; D018087:Plastids / Q000235:genetics; D032107:Populus / Q000145:classification* / Q000235:genetics*; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D018744:DNA, Plant
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