Species delimitation of Melia dubia Cav. from Melia azedarach L. complex based on DNA barcoding

The genus Melia L, which belongs to the Mahogany family Meliaceae, is a source of important phytochemicals with marked medicinal properties. Species identification in Melia is complex due to the existence of overlapping morphological features. Although Melia dubia Cay. is listed as a synonym of Melia azedarach L, it is not clear from the available literature whether they are the same species or different, and the species complexity still remains unresolved. In the present study, 10 accessions of M. dubia and M. azedarach were analysed by DNA barcoding using three chloroplast DNA markers (rbcL, matK, and trnH-psbA), and one nuclear marker (ITS2). Intraspecific divergence was not found in any of the four markers. However, the interspecific divergence between M. azedarach and M. dubia ranged between 0.3% (rbcL) and 4.7% (ITS2) for individual markers, and for the combined dataset, it was 8.5%. Among the four markers, ITS2 was found to be the most suitable marker for differentiating M. azedarach and M. dubia. Parsimony analysis of the DNA barcoding data showed a clear segregation between M. azedarach and M. dubia as distinct monophyletic clades in all the markers, except the rbcL marker. Our results based on Bayesian analysis of the concatenated dataset strongly support the view that M. dubia be considered a distinct species; not a synonym of M. azedarach.