Away from the primary domestication center, the Far-West diversification area of the olive tree: towards the management of Moroccan natural resources.

Abstract

Background and aims: Olive (Olea europaea L. subsp. europaea) is one of the most widespread woody crops in the Mediterranean Basin (MB) existing in two forms, namely the wild (or oleaster) and the cultivated olive (varieties). In its southwestern most distribution range, Morocco is an area of primary interest, as it is both a genetic hotspot for wild olives and a diversification center for the cultivated form. This study aimed to deepen understanding of the evolutionary history of olive trees in this geographic area.

Methods: A total of 221 oleasters from 25 populations across eight geographical regions were collected along a north-south gradient and analysed using both nuclear and plastid DNA markers, alongside 306 well-known Mediterranean olive varieties. The genetic status of wild olives and the environmental factors potentially driving their genetic structure were investigated.

Key results: Local wild olives and Mediterranean varieties displayed similar levels of genetic diversity and richness, while local oleasters were mostly assigned to a distinct gene pool. Two seed-propagated olive forms were genetically identified: genuinely wild and feral olives near olive cropping areas, suggesting gene flow between wild and clonally propagated olives. The E3 matrilineage was predominant in northwestern Morocco, with endemic haplotypes supporting the assumption that this region served as a long-term refugium for the oleaster. A north-south genetic structure of genuine wild olives was revealed, likely driven by an ancient split in their distribution due to palaeoclimatic and palaeobiogeographic factors, further influenced by human activities.

Conclusions: Environmental and anthropogenic factors, including climate and human-driven land-use changes, may have shaped the current distribution of wild olive populations in the extreme southwestern MB. In the context of ongoing climate changes, understanding evolutionary history and identifying diversity hotspots are crucial for guiding efforts to develop cost-effective conservation strategies of natural resources.