Summary: Whether sex chromosomes are differentiated is an important aspect of our knowledge of dioecious plants, such as date palm (Phoenix dactylifera). In this crop plant, the female individuals produce dates, and are thus the more valuable sex. However, there is no way to identify the sex of date palm plants before reproductive age, and the sex‐determining mechanism is still unclear. To identify sex‐linked microsatellite markers, we surveyed a set of 52 male and 55 female genotypes representing the geographical diversity of the species. We found three genetically linked loci that are heterozygous only in males. Male‐specific alleles allowed us to identify the gender in 100% of individuals. These results confirm the existence of an XY chromosomal system with a nonrecombining XY‐like region in the date palm genome. The distribution of Y haplotypes in western and eastern haplogroups allowed us to trace two male ancestral paternal lineages that account for all known Y diversity in date palm. The very low diversity associated with Y haplotypes is consistent with clonal paternal transmission of a nonrecombining male‐determining region. Our results establish the date palm as a biological model with one of the most ancient sex chromosomes in flowering plants.

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.

Germination of 2000-year-old seeds of Phoenix dactylifera from Judean desert archaeological sites provides a unique opportunity to study the Judean date palm, described in antiquity for the quality, size, and medicinal properties of its fruit, but lost for centuries. Microsatellite genotyping of germinated seeds indicates that exchanges of genetic material occurred between the Middle East (eastern) and North Africa (western) date palm gene pools, with older seeds exhibiting a more eastern nuclear genome on a gradient from east to west of genetic contributions. Ancient seeds were significantly longer and wider than modern varieties, supporting historical records of the large size of the Judean date. These findings, in accord with the region’s location between east and west date palm gene pools, suggest that sophisticated agricultural practices may have contributed to the Judean date’s historical reputation. Given its exceptional storage potentialities, the date palm is a remarkable model for seed longevity research.

Due to the economic importance of the date palm in Tunisia, we attempt to develop microsatellite markers for the genetic characterisation and identification of cultivars. This characterisation will enable us to obtain an extensive understanding of the local genetic diversity and its distribution. Fourteen microsatellite loci of Phoenix dactylifera L. were tested to examine the genetic diversity in the Tunisian date palm germplasm: 74 female and 27 male cultivars were represented. A total of 136 alleles and 311 genotypes were detected based on 14 loci microsatellite. A high level of polymorphism was detected at the DNA level. The 101 date palms from three main oases exhibited a high degree of generic diversity and were structured independently of their geographical origin and sex. All the local date palm accessions were successfully fingerprinted and easily distinguished based on only five loci. The possibility of using microsatellites in the large-scale molecular labelling of offshoots and in vitro plantlets and in the certification of plant material is discussed

• Premise of the study: To complement existing sets of primarily dinucleotide microsatellite loci from noncoding sequences of date palm, we developed primers for tri‐ and hexanucleotide microsatellite loci identified within genes. Due to their conserved genomic locations, the primers should be useful in other palm taxa, and their utility was tested in seven other Phoenix species and in Chamaerops, Livistona, and Hyphaene.• Methods and Results: Tandem repeat motifs of 3–6 bp were searched using a simple sequence repeat (SSR)–pipeline package in coding portions of the date palm draft genome sequence. Fifteen loci produced highly consistent amplification, intraspecific polymorphisms, and stepwise mutation patterns.• Conclusions: These microsatellite loci showed sufficient levels of variability and transferability to make them useful for population genetic, selection signature, and interspecific gene flow studies in Phoenix and other Coryphoideae genera.