Molecular polymorphism and phylogenetic relationships within Tunisian date palm (Phoenix dactylifera L.): Evidence of non-coding trnL-trnF regions of chloroplast DNAs

- We analyze molecular diversity and genetic relationships in Tunisian date palm.
- The polymorphism pattern reveals an elevated level of mutation point.
- Analyzed sequences allow the establishment of relationships between cultivars.
- The cytoplasmic diversity suggests a rapid population expansion.
- Absence of a biogeographic repartition of the variability.

Phoenix dactylifera L. were analyzed for DNA sequence diversity in the non-coding region of chloroplast DNA. The trnL-trnF intergenic spacer sequences were used as genetic markers to establish refined genetic relationships for differentiating date-palm accessions collected from Tunisian oasis. A single DNA band of approximately 400 bp was amplified from each Tunisian date-palm cultivars. Using the Kimura-2 method, nucleotide sequences were aligned using the MEGA 5.2 program to calculate pairwise divergence of trnL-trnF spacer sequences between cultivars. The relatively high AT values (60.5-67.6%) of trnL-trnF intergenic spacer may explain the high proportion of the identified transversions (ti/tv = 0.67). These results suggest the rate of nucleotide diversity with a great variation level of chloroplast non-coding region. The analyzed data illustrated a considerable level of variability in the genetic pool of the local germplasm. In fact, relationships inferred from the cpDNA analysis suggest several clades, which do not show geographical correspondence. In the other hand, 14 haplotypes were detected among 31 individuals examined, yielding a haplotype diversity of 0.854 and a level of nucleotide diversity of (0.0081). Selective neutrality tests show that Tajima's as well as Fu and Li's tests were negative and not significant in the studied cultivars. The cytoplasm variability indicates a narrow genetic base within date-palm cultivars. The opportunity of the designed methods is discussed with the molecular characterization of genotypes in order to enhance the conservation and the improvement of the local date-palm germplasm.