The Laperrine's olive tree (Oleaceae): a wild genetic resource of the cultivated olive and a model-species for studying the biogeography of the Saharan Mountains

The Laperrine's olive is an iconic subspecies of Olea europaea (Oleaceae) with a narrow distribution in the Saharan Mountains, from south Algeria to northeast Sudan. Recently, population genetic and phylogeographic studies gave insights on its reproductive strategies, its history since the Pleistocene, and its putative utility as a genetic resource of the cultivated olive. In natural habitats, multi-centennial individuals occur in very harsh environmental conditions and mainly reproduce vegetatively, but it appears that sexuality may be easily restored under favourable conditions. Crosses between the Laperrine's olive and other olive diploid subspecies (subspp. cuspidata and europaea) have been recently reported. Plastid DNA analyses also indicate that the Laperrine's olive has already been used during the secondary diversification of the cultivated Mediterranean olive in the Maghreb. This taxon could therefore be used as source of genes for the breeding of new olive cultivars, particularly to improve drought tolerance. In this review, we also address the potential utility of this taxon for studying the self-incompatibility genetic determinism and the polyploidy origin in O. europaea. Phylogeographic studies attested that Laperrine's olive populations show affinities with both the Mediterranean and sub-Saharan olive taxa, but the high genetic differentiation between populations indicates that gene exchanges between massifs were limited or inexistent for a long time. Dating these events remains a challenge for determining in which environmental conditions these populations have been separated. Further comparisons of phylogeographic patterns and reproductive strategies between various plant groups are required to improve knowledge on the biogeography of Saharan mountains and may help to define appropriate conservation strategies of their threatened ecosystems.