Sequence analysis and molecular evolution of Tunisian date palm cultivars (Phoenix dactylifera L.) based on the internal transcribed spacers (ITSs) region of the nuclear ribosomal DNA

Sequences of the internal transcribed spacers (ITSs) of nuclear ribosomal DNA (nrDNA) were studied in 15 Tunisian date palm accessions (Phoenix dactylifera L.) in order to establish genetic relationships among date palm cultivars and to elucidate its molecular evolution. The length size of the ribosomal intergenic spacer ranged from 441 bp and 445 bp. Variation of GC contents has been scored as 45.6-46.5% in the ITS region. The overall transition/transversion bias R is 4.375 indicating that the transitions are more frequent than transversions at this region. The aligned Sequences allowed us to identify 4 haplotypes among the 15 examined cultivars. Intraspecific variation has been occurred in sequences of the internal transcribed spacers (ITSs) of date palm. The haplotypic and nucleotide diversities appeared low. Phylogenetic trees generated using distance (Neighbor joining) and maximum parsimony (MP) methods supported significantly the organization of the tested accessions that are ordered independently of the tree's sex and the chlorotype classification. This gives evidence of an unstructured geographic pattern among the studied cultivars. Molecular evolution analysis demonstrates that the ribosomal intergenic spacer ITS evolved under a strictly neutral model. A stable population of Tunisian date palm seems to be retained within the studied genotypes. Our results indicate that the diversity detected among closely related genotypes supported strongly the efficiency of ITS sequences for establishing relationships between cultivars and determining the evolutionary history of this species.