Olea europaea - EUFORGEN European forest genetic resources programme

Genetic summary

Genetic diversity and variation

Olive genetic diversity is high but shaped mainly by cultivation history and local selection. Diversity is structured by accession origin and use (fruit exploitation, ecological adaptation), with strong genetic differentiation between cultivars within Mediterranean zones and low variability between zones (Belaj et al., 2002; Gemas et al., 2004;). Most genetic diversity exists between genotypes within countries rather than between regions, reflecting centuries of cultivar intercrossing, wild–cultivated hybridization, and clonal propagation (Belaj et al., 2002).

Portuguese cultivars show high diversity, partly because sexually produced seedlings were historically incorporated into vegetatively propagated stocks (Gemas et al., 2004). Low interspecific differentiation within olive suggests recent divergence, past gene flow, or human-mediated movement of germplasm (Besnard et al., 2001).

Genetic distribution and clustering

Genetic structure in olive populations is closely linked to local adaptation and human selection for fruit traits and agroecological conditions (Gemas et al., 2004). Studies show clear relationships between genetic and geographic distances across the Mediterranean (Besnard et al., 2001). Cluster analyses reveal three major genetic groups: one group of cultivars from the eastern and central Mediterranean, a second of Italian and Spanish cultivars, and a third group from the western Mediterranean zone (Belaj et al., 2002). Sub clustering within countries also occurs, showing local genetic differentiation due to regional selection (Gemas et al., 2004). A pronounced east–west cline in genetic variation exists across the Mediterranean in olive, and olives from the Middle East and Türkiye are genetically distinct from other Mediterranean populations (Besnard et al., 2001; Breton, Tersac, and Bervillé, 2006).

Wild olives from the western Mediterranean are genetically distinct from cultivated forms, suggesting independent evolutionary lineages (Besnard, Baradat, and Bervillé, 2001). However, extensive human-mediated movement and selection have blurred the natural boundaries between wild and cultivated gene pools, complicating the reconstruction of olive’s genetic distribution.

Gene flow

Olive pollen is wind-dispersed, enabling local cross-pollination, while seeds are mainly animal dispersed over short to moderate distances. However, long-distance gene flow has been driven by humans through trade, migration, and movement spreading cultivated olives and promoting admixture with wild olives over great distances, shaping the Mediterranean genetic landscape. (Breton, Tersac, and Bervillé, 2006).

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.

Further relevant genetic traits

Interspecific taxa dynamics

Olives includes several closely related taxa, notably North African wild olive (Olea europaea subsp. laperrinei), Moroccan wild olive (Olea europaea subsp. maroccana), and Canarian olive (Olea europaea subsp. guanchica), which are the most genetically like the Mediterranean olive, while African wild olive (Olea europaea subsp. africana) is the most distant (Besnard et al., 2001). Despite this, hybrids between African wild olive and European olive have been documented, indicating sexual intercompatibility (Besnard, Baradat, and Bervillé, 2001; Besnard et al., 2001). Geographic isolation, climatic fluctuations, and population contractions followed by expansions have contributed to divergence and regional structuring of genetic diversity (Besnard, Baradat, and Bervillé, 2001). However, olive still has uncertain origins (Besnard et al., 2001). Morphological and genetic variation is shaped by isolation and hybridization, producing distinct eastern and western populations yet maintaining interspecific gene flow within olive species (Besnard, Baradat, and Bervillé, 2001).

Cultivation and human intervention

Olive is one of the earliest domesticated and most important oil-producing crops in the Mediterranean (Besnard et al., 2001; Belaj et al., 2002). Domestication began in the Neolithic from wild olives in the eastern Mediterranean, with cultivars later spreading westward through human migration and trade (Besnard, Baradat, and Bervillé, 2001; Besnard et al., 2001; Breton, Tersac, and Bervillé, 2006). Over millenniums, local farmers selected and propagated cultivars vegetatively based on agronomic performance and adaptation to local environments (Gemas et al., 2004). This process led to strong regional differentiation and high genetic diversity between cultivars. Some ancient cultivars, such as ‘Galega’ in Portugal, dominate regional heritage (Gemas et al., 2004). Despite movement of genetic material, multiple selection events produced genetically distinct pools across the Mediterranean (Besnard, Baradat, and Bervillé, 2001). Human-driven dispersal, hybridization with wild olives, and long-term local selection together shaped the current complex genetic structure of olive populations.

Glacial biogeography evolution

European olive genetic diversity is structured into regions that correspond to glacial refugia (Breton, Tersac, and Bervillé, 2006). Following the Last Glacial Maximum, recolonization of the Mediterranean basin occurred from both eastern and western refuges, creating a gradient of genetic diversity across populations. This postglacial expansion and long-term isolation in refugial zones contributed to regional genetic differentiation within olive, shaping the present-day east–west genetic structure observed among wild and cultivated olives (Breton, Tersac, and Bervillé, 2006).

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.

Genetic conservation

Threats

The genetic integrity of olive is threatened by the widespread transposition of cultivars across regions, which can disrupt locally adapted genetic structures and reduce regional genetic distinctiveness (Gemas et al., 2004). Human-mediated selection and long-term vegetative propagation may also limit genetic recombination, leading to reduced diversity within modern cultivated populations.

Management

Conservation and improvement of olive genetic resources require careful management of cultivar movement and targeted genetic conservation. Breeding programmes should prioritize the use of autochthonous cultivars, as significant genetic variability exists within national germplasm (Belaj et al., 2002). Expanding germplasm collections to include cultivars from across the Mediterranean basin can ensure representation of the species’ full variability (Belaj et al., 2002). Moreover, related taxa outside the Mediterranean olive group could serve as valuable genetic resources for improving traits such as disease resistance and fruit quality (Besnard, Baradat, and Bervillé, 2001).

The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.

Olea europaea
Olive tree

Environmental zones

Status of Olea europaea conservation in Europe

Genetic summary

Genetic diversity and variation

Genetic distribution and clustering

Gene flow

Further relevant genetic traits

Interspecific taxa dynamics

Cultivation and human intervention

Glacial biogeography evolution

Genetic conservation

Threats

Management

Genetic Characterisation of Olea europaea and its GCUs

Availability of FRM

Further reading

References

Olea europaeaOlive tree

Environmental zones

Status of Olea europaea conservation in Europe

Genetic summary

Genetic diversity and variation

Genetic distribution and clustering

Gene flow

Further relevant genetic traits

Interspecific taxa dynamics

Cultivation and human intervention

Glacial biogeography evolution

Genetic conservation

Threats

Management

Genetic Characterisation of Olea europaea and its GCUs

Availability of FRM

Further reading

References

Olea europaea
Olive tree