Genetic and Phenotypic Variations Within Ancient ‘Mehras’ Olive (Olea europaea L.)

Ancient olives are considered a major resource of gene pool, adapted across ages to ever changing environments. The ancient ‘Mehras’ olive is the only cultivar inscribed on the UNESCO Representative List of the Intangible Cultural Heritage Of Humanity as recognized for its longevity and historical significance. However, detailed genetic and phenotypic analyses are still missing. Nineteen ‘Mehras’ accessions were collected from northern Jordan and subjected to inter-simple sequence repeat (ISSR) marker analysis and to a set of phenotypic parameters (leaf, fruit, and stone). ISSR analysis revealed similarity values ranging between 0.53 and 1.00, indicating moderate to high genetic diversity. Bayesian clustering and dendrogram analyses identified two major genetic clusters with limited admixture, indicating extended clonal propagation in addition to the transport of planting material. Phenotypic parameters revealed tangible variation among accessions, with major influence of fruit and stone traits followed by leaf traits. Strong correlations were observed between key traits, including fruit width and flesh thickness, while an inverse relationship was observed between flesh and stone percentages. Multivariate analysis further revealed clear separation among investigated accessions. The Mantel test showed a moderate correlation between genetic and phenotypic distances. Spatial analysis suggested weak geographic structuring of diversity, indicating exchange of plant material. ‘Mehras’ olive harbors structured genetic and phenotypic diversity influenced mainly by adaptation and traditional cultivation practices. These findings provide a foundation for conservation, breeding, and sustainable utilization of this ancient and culturally significant cultivar.