Molecular Phylogeny of Aegilops L. and Triticum L. Species Revealed by Internal Transcribed Spacers of Ribosomal Genes

Phylogenetic analysis of Triticum L. and Aegilops L. species was performed using the nuclear ribosomal Internal Transcribed Spacer (ITS) sequences. The full length of PCR products for ITS1 and ITS2 ranged from 650 bp to 700 bp, respectively. Sequence divergences between species were estimated following aligning. The average G+C contents of the ITS regions was 60.8% for ITS2 and 61.5% for ITS1. The phylogenetic analyses were constructed using the Neighbor-Joining (NJ) method based on pairwise genetic distances. The resulting NJ tree successfully separated Triticum and Aegilops species and displayed three clusters, einkorn wheats, polyploid wheats, and Aegilops. Our results confirmed that the A genome of bread wheat is more related to T. urartu than T. boeticum. In the case of the D genome, the affinity between Ae. tauschii and bread wheat was greater than other D genome-bearing species of Aegilops (Ae. crassa and Ae. cylindrica). Obtained results also revealed that Ae. speltoides was separated from Aegilops cluster and grouped with polyploid wheats. The close relationship between Ae. speltoides and polyploid wheats indicates that the former is the most likely donor of the B genomes to wheats. The present study verified the potential of ITS regions in phylogenetic studies and strongly supported the evolution of cultivated wheats, which occurred through hybridization and polyploidization between Triticum and Aegilops species.