Towards the identification of wild African date palms in Kerkennah Islands from Tunisia by morphometric and genetic analyses

Wild relatives constitute an invaluable resource for crop breeding and are key components to understand their domestication history. Date palm is one of the oldest fruit crops, cultivated for millennia for its nutritional value and major economic and symbolic role. Two strongly differentiated gene pools have been recognized as the Western gene pool in North Africa and the Eastern one in the Middle East. Although a wild population has been proposed in Oman for the Eastern genetic pool, no wild date palm from the Western one has been yet described. In Tunisia, the date palms of Kerkennah archipelago consisted of spontaneous uncultivated individuals that are promising candidates for putative wild date palms. Morphometric tools were applied to 1140 date palm seeds of 69 Kerkennah accessions and compared to previously defined reference morphotypes. The genetic diversity of Kerkennah accessions was also compared to date palm populations and three Phoenix species using 18 nuclear microsatellite and one chloroplastic minisatellite markers. Morphometric analyses of Kerkennah accessions revealed genotypes with round-shaped seeds, characteristic of wild Phoenix species. Genetic analyses showed that Kerkennah's date palm belonged to the Western gene pool and exhibited a larger diversity and allelic richness than the western cultivated ones, proving that they are more probably wild than ferals. Altogether, our results strongly suggest that the spontaneous date palms growing in the harsh environment of the Kerkennah archipelago are wild populations. This unique heritage long-time preserved from anthropogenic pressure, is likely to contain some of the ancestral genetic diversity that would be of great value for breeding and provides new information for the discovery of the origins of the date palm.