DNA Barcoding: Unsuccessful for Species Identification in Fragaria L.

The USDA-ARS National Clonal Germplasm Repository (NCGR) in Corvallis, Oregon, maintains more than 1500 Fragaria accessions representing 22 species collected from 37 countries. Species designation is currently based on the published species descriptions which depend on geographical origin and morphological traits that exhibit limited variation. Our objective was to assess a simple DNA-based technique, DNA barcoding for the ability to identity Fragaria species. Two recommended plant DNA barcodes, the nuclear ribosomal internal transcribed spacer (nrITS) and chloroplast spacer psbA-trnH, were tested. The 'barcoding gap', between within species and between species variation, was absent preventing successful identification of Fragaria species. Cluster analysis using nrITS supported F. mandschurica as the maternal donor to the octoploids. Two (Y and Z) of the three defined diploid Fragaria clades (X, Y, and Z) were identified using nrITS, while the chloroplast psbA-trnH contained little variation. The psbA-trnH spacer could only identify F. bucharica and F. nilgerrensis due to characteristic deletions in this chloroplast region. Neither of the two sequences, singly or in combination, could identify each of the Fragaria species. Therefore, DNA barcoding using universal sequences is not an adequate technique for species identification in Fragaria.