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.Methodology/Principal FindingsHere, 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/SignificanceIn 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).
Highlights
The species within the genus Populus are one of the world’s most important groups of forest trees: they are widespread and play a significant role in the ecosystem of temperate and boreal forests across the northern hemisphere [1,2]
The PWG-Distance method recommended by the CBOL Plant Working Group [15] employs distances calculated from pair-wise alignments counting unambiguous base substitutions only, and pair-wise pdistances were calculated using PAUP* 4.0b10 [49] and we considered discrimination to be successful if the minimum uncorrected interspecific p-distance involving a species was larger than its maximum intraspecific distance
Problems were encountered in the sequencing of trnH–psbA, where a mono-nucleotide repeat (poly(A)) fragment in the middle part of this region lead to sequencing failure of the latter half of this region for most individuals
Summary
The species within the genus Populus (collectively known as poplars) are one of the world’s most important groups of forest trees: they are widespread and play a significant role in the ecosystem of temperate and boreal forests across the northern hemisphere [1,2]. Identification of the wild Populus species is still difficult because of their extensive interspecific hybridization and high levels of intraspecific morphological variation [2,9,10,11]. The recently developed DNA barcoding approach is one way to address this problem. 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
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
