RFLP analysis of nuclear DNA for study of phylogeny and domestication of tetraploid wheat

To study the phylogeny and domestication of tetraploid wheat species, variations in nuclear DNA of the cultivated and wild species were investigated by RFLP analysis. Twenty-two accessions representing 11 species of cultivated tetraploid wheat (Emmer wheat and Timopheevi wheat), 16 accessions of wild Emmer wheat (Triticum dicoccoides Körn.), 14 accessions of wild Timopheevi wheat (T. araraticum Jakubz.), and an accession of common wheat (T. aestivum) were analyzed, using 29 combinations of two restriction enzymes and 20 probes. Based on this result, the genetic distances (d) between all pairs of accessions were estimated. An average d was 0.0189 in the Emmer group and 0.0024 in the Timopheevi group, while that between the groups was 0.0698. Cluster analysis using UPGMA, NJ (neighbor joining) and maximum parsimony method showed clear differentiation of Emmer wheat and Timopheevi wheat. Among the cultivated Emmer wheat T. dicoccum Schübl. showed the largest nucleotide diversity (π = 0.0180) which was close to that (0.0186) in the wild ancestral species, T. dicoccoides. All the cultivated species, except for T. dicoccum and T. paleocolchicum Men., were grouped into a distinct cluster in the phylogenetic trees. All but one accessions of T. dicoccoides were grouped in another. The large genetic diversity in T. dicoccum, the non-free threshing species, supports the archeological evidence that T. dicoccum was the earliest domesticated tetraploid wheat.