DNA Barcodes Distinguish Withania somnifera and Withania ashwagandha

Abstract

On the basis of morphology, chemical profiling, crossing ability, amplified fragment length polymorphism and comparison of nucleotide sequences of nuclear ribosomal internal transcribed spacer (ITS), the cultivated form of Withania somnifera, a species of therapeutic value, has been circumscribed as a new species, Withania ashwagandha. The present study was undertaken to ascertain whether the two species can be distinguished on the basis of DNA barcoding. Six barcode loci, ITS, ITS2, matK (maturase K), rbcL (ribulose-bisphosphate carboxylase/oxygenase, large subunit), rpoC1 (RNA polymerase-β′ subunit, main catalytic subunit) and trnH-psbA spacer (transfer RNA for histidine-photosystem II protein D1 spacer) from W. somnifera, W. ashwagandha, their hybrid, and ‘ashwagandha’ market samples were amplified, sequenced, and compared. ITS, ITS2 and matK distinguished two species on the basis of phylogenetic tree method. Likewise, BLAST 1 analysis based on ITS, ITS2, matK, and rbcL individually discriminated two species. However, on the basis of Kimura 2 Parameter distances, two species could not be distinguished as the requirement of a distinct barcode gap—the highest intraspecific distance being lower than the lowest interspecific distance—was not met by any of the loci. If compared by character-based method, ITS, ITS2 and matK sequences of the two species had distinct diagnostic nucleotides (pure character attributes) at nine, four and one positions, respectively. Interestingly, all market samples co-segregated and shared character attributes with W. ashwagandha.