Unveiling the Genetic Diversity of Tunisian Monumental Olive Trees to Enhance the Olive Sector

The centennial olive trees of Tunisia serve as enduring symbols of resilience, having withstood the test of time while bearing witness to the effects of climate change, rising temperatures, water scarcity, and the emergence of new diseases. Presently, there is a notable lack of research on the genomic analysis of ancient trees. This study investigates the genomes of twenty-eight ancient olive specimens collected from archaeological sites. It uses nine highly polymorphic microsatellite markers to compare these ancient genomes with twenty-five local Tunisian cultivars and sixty olive varieties from the Mediterranean countries. The study revealed high genetic diversity among ancient olive trees, with 67 alleles and a Shannon index of 1.68, surpassing Tunisian cultivars. Key findings identify the ancient trees M25, M1, M28, and M24 as synonyms for local olive cultivars, while "M10" is noted as a first-generation migrant from Tunisian olives. Cluster analysis methods, including structure, neighbor-joining (NJ), and principal coordinates (PCoA), demonstrate that these ancient trees share a common genetic background and ancestry with varieties from Tunisia, Italy, Spain, and Greece. Therefore, conserving and valuing these genotypes will enhance the genetic diversity available for breeding programs and strengthen the resilience of agriculture, which is currently facing unprecedented pressures worldwide.