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Abstract:
Olive is a species domesticated from the closely related wild olive in the Mediterranean basin. The use of clonal propagation and the long-lived nature of the trees have created the conditions for pluri-centenarian olives that are considered relicts of ancient, once predominant, and in a few cases abandoned genotypes. We analyzed the genomes of 22 old olives, 20 of them survived either within and nearby archeological sites or in rural settlements outside of modern orchards in Southern Italy, in Sicily and Sardinia islands, from Aegean Sea to shade light on the origin of modern olive cultivars. Using a newly generated chromosome-scale reference genome of the cv. Leccino, we compared old olive genomes with the genome of 71 cultivars, representing the olive-growing areas in the Mediterranean basin, and 11 spontaneous trees from the Western Mediterranean Basin. Then, the entire set of olive genomes was compared with a pan-Mediterranean olive diversity panel made of more than 450 accessions genotyped with different technologies. All Western cultivars showed Eastern ancestry and a couple of Eastern cultivars were highlighted as main founders of both ancient and modern genotypes from the East and the West. We also found evidence that Western oleasters hybridized with cultivars of Eastern origin giving rise to Western cultivars. The genome analysis suggested that only a few generations of sexual reproduction separate cultivated olive from its wild ancestor, a finding that suggests an ample room for improvement of cultivated olive.
