Sequences Evolution and Population Structure of Tunisian Date Palm (Phoenix dactylifera L.) Revealed by Chloroplast DNA Markers

Abstract

Date palm is present among the vital crops of arid and semiarid countries of North Africa and the Middle East. Chloroplast DNA is the best molecule for finding the evolutionary history of plant species. In the present study, cpDNA variation in date palm was estimated using the trnL-trnF intergenic spacer and psbZ-psbC region. The high AT values in both molecular markers may clarify the high proportion of transversions observed in this species. The neutrality tests, expansion parameter estimation (mismatch distribution), and haplotype network patterns proposed that demographic expansion had occurred in recent times. Furthermore, the taxa distribution is not related to geographical origins; neighbor-joining trees are clustered independently either from their geographic origin or from the sex of trees, suggesting a common genetic basis between different cultivars. Statistical analysis of chloroplast germplasm provides a means of assessing cytoplasmic gene flow, which occurred in Tunisian Phoenix dactylifera L. In fact, Nm was important between Tunisia and Eastern Arabic region (Nm = 2.57), which reflects high levels of connectivity between these population pairs. In conclusion, genomic studies prove date palm domestication happened in the Arabian Peninsula and showed an important gene flow with North African palm populations.