Biogeography of the date palm (Phoenix dactylifera L., Arecaceae): insights on the origin and on the structure of modern diversity

AGAP : équipe Génomique évolutive et gestion des populations (GE²pop)The biogeography of the date palm (Phoenix dactylifera L.), the origin, structure and dynamics of its agrobiodiversity, and the relationships to other species of Phoenix are reviewed. Phoenix dactylifera is confirmed as a distinct species and has closest affinities with P. sylvestris and P. atlantica. Multiple origins of domestication are likely, within two highly distinct primary gene pools, one oriental (Middle East) and one occidental (south-western Europe and north-western Africa), subsequently partially admixed, especially in the intermediate zone of North Africa. A rationale to identify wild populations of P. dactylifera, using a combination of chloroplast barcoding and nuclear microsatellite genotyping is proposed. A domestication model is presented and the domestication syndrome is described, as well as the nature of cultivars. All data indicate a strong geographic structure of the genetic diversity of the date palm at all scales (local, regional, global), and the importance of both isolation and intraspecific gene flow in shaping the present day agrobiodiversity, while there is no evidence of interspecific hybridization in the cultivated gene pool

Genetic structure of the date palm (Phoenix dactylifera) in the Old World reveals a strong differentiation between eastern and western populations

Background and Aims Date palms (Phoenix dactylifera, Arecaceae) are of great economic and ecological value to the oasis agriculture of arid and semi-arid areas. However, despite the availability of a large date palm germplasm spreading from the Atlantic shores to Southern Asia, improvement of the species is being hampered by a lack of information on global genetic diversity and population structure. In order to contribute to the varietal improvement of date palms and to provide new insights on the influence of geographic origins and human activity on the genetic structure of the date palm, this study analysed the diversity of the species. Methods Genetic diversity levels and population genetic structure were investigated through the genotyping of a collection of 295 date palm accessions ranging from Mauritania to Pakistan using a set of 18 simple sequence repeat (SSR) markers and a plastid minisatellite. Key Results Using a Bayesian clustering approach, the date palm genotypes can be structured into two different gene pools: the first, termed the Eastern pool, consists of accessions from Asia and Djibouti, whilst the second, termed the Western pool, consists of accessions from Africa. These results confirm the existence of two ancient gene pools that have contributed to the current date palm diversity. The presence of admixed genotypes is also noted, which points at gene flows between eastern and western origins, mostly from east to west, following a human-mediated diffusion of the species. Conclusions This study assesses the distribution and level of genetic diversity of accessible date palm resources, provides new insights on the geographic origins and genetic history of the cultivated component of this species, and confirms the existence of at least two domestication origins. Furthermore, the strong genetic structure clearly established here is a prerequisite for any breeding programme exploiting the effective polymorphism related to each gene pool