The olive (botanical name “Olea europaea”, meaning “European olive”) is a species of evergreen tree or shrub in the family of Oleaceae in the order of Lamiales. The tree is typically short and squat, seldom taller than 26 – 49 feet (8 – 15 meters). The trunk is gnarled and twisted.
With a sturdy and extensive root system, the olive tree can tolerate drought well, live for centuries, and remain productive for long periods if pruned correctly and regularly.
Hundreds of cultivars (assemblage of plants selected for desirable characters that are maintained during plant propagation) of the olive tree are known.
Many olive cultivars are self-sterile (self-incompatible; when a pollen grain produced in a plant reaches a stigma of the same plant or another plant with a similar genotype, the process of pollen germination, pollen-tube growth, ovule fertilization and embryo development is halted at one of its stages and consequently no seeds are produced). Olive trees are generally planted in pairs with a single primary cultivar and a secondary cultivar selected for its ability to fertilize the primary one.
Only a few olive varieties can be used to cross-pollinate. Olive trees are, then, propagated by various other methods, including grafting (in Greece grafting the cultivated tree on the wild tree is a common practice) and budding (asexual reproduction; in Italy, for instance, embryonic buds, which form small swellings on the stems, are excised and planted under the soil surface).
With common ancestors that go way (way) back, long before written history (“the most recent common ancestor of each Mediterranean lineage dates back to the Middle or Upper Pleistocene: 139 100 BP for E1 (95% CI: 49 200–482 100), 284 300 BP for E2 (95% CI: 84 400–948 100) and 143 700 BP for E3 (95% CI: 37 100–542 700″), the olive tree was first domesticated in the Eastern Mediterranean between 8,000 and 6,000 years ago, according to research published in February 2013 in the “Proceedings of the Royal Society B (Biological Sciences): “The complex history of the olive tree: from Late Quaternary diversification of Mediterranean lineages to primary domestication in the northern Levant.”
We can say there were probably several steps, and it probably starts in the Levant,” or the area that today includes Israel, Palestine, Jordan, Lebanon and Syria, said study co-author Gillaume Besnard, an archaeobotanist at the National Center for Scientific Research in France. “People selected new cultivars everywhere, but that was a secondary diversification later.”
The findings, published in the journal Proceedings of the Royal Society B, are based on the genetic analysis of nearly 1,900 samples from around the Mediterranean Sea. The study reveals that domesticated olives, which are larger and juicier than wild varieties, were probably first cultivated from wild olive trees at the frontier between Turkey and Syria.
Tia Ghose, “The Origins of the Olive Tree Revealed,” LiveScience, 5 February 2013
The cradle of primary domestication of the olive tree is located in the northeastern Levant, where populations currently contain substantial genetic diversity, although not the highest in the Mediterranean basin (i.e. the Strait of Gibraltar [13,43]). This paradox can be explained by the fact that advanced civilizations emerged in the north Levant, such as the Pre-Pottery Neolithic B [51,52], and that they had enough genetic resources to succeed in domesticating a self-incompatible tree. The domestication of the olive tree appears to have been a long and continuous process that involved numerous genetic exchanges between the cultivated trees and wild gene pools, as already reported for other crops [53]. The first domesticated gene pool of olive was more likely to have spread with agriculture, first to the whole Levant and Cyprus [54] before being progressively disseminated to the western Mediterranean. Genetic evidence for multi-local origins of cultivars previously reported by several authors [6–12,55] may be explained by secondary domestication events involving crosses between newly introduced cultivars and local oleasters across the entire Mediterranean.
Besnard G, Khadari B, Navascues M, Fernandez-Mazuecos M, El Bakkali A, Arrigo N, Baali-Cherif D, Brunini-Bronzini de Caraffa V, Santoni S, Vargas P, Savolainen V. 2013 “The complex history of the olive tree: from Late Quaternary diversification of Mediterranean lineages to primary domestication in the northern Levant“. Proc R Soc B 280: 20122833. http://dx.doi.org/10.1098/rspb.2012.2833
To unravel the history of the olive tree, the team took 1,263 wild and 534 cultivated olive tree samples from throughout the Mediterranean and analyzed genetic material from the trees’ chloroplasts, the green plant structures where photosynthesis takes place. Because chloroplast DNA is passed from one tree to the descendant trees that spring up around it, the DNA can reveal local changes in plant lineages, study co-author Gillaume Besnard, an archaeobotanist at the National Center for Scientific Research, said.
The researchers then reconstructed a genetic tree to show how the plant dispersed. The team found that the thin, small and bitter wild fruit first gave way to oil-rich, larger olives on the border between Turkey and Syria.
After that first cultivation, modern-day domesticated olives came mostly from three hotspots: the Near East (including Cyprus), the Aegean Sea and the Strait of Gibraltar. They were then gradually spread throughout the Mediterranean with the rise of civilization.
Tia Ghose, “The Origins of the Olive Tree Revealed,” LiveScience, 5 February 2013
See:
Besnard G, Khadari B, Navascues M, Fernandez-Mazuecos M, El Bakkali A, Arrigo N, Baali-Cherif D, Brunini-Bronzini de Caraffa V, Santoni S, Vargas P, Savolainen V. 2013 “The complex history of the olive tree: from Late Quaternary diversification of Mediterranean lineages to primary domestication in the northern Levant“. Proc R Soc B 280: 20122833. http://dx.doi.org/10.1098/rspb.2012.2833
Author for correspondence:
G. Besnard
e-mail: guillaume.besnard@univ-tlse3.fr
Electronic supplementary material is available at http://dx.doi.org/10.1098/rspb.2012.2833 or via http://rspb.royalsocietypublishing.org.
Tia Ghose, “The Origins of the Olive Tree Revealed,” LiveScience, 5 February 2013
“Olive,” Wikipedia
“Budding,” Wikipedia
“Plant Propagation,” Wikipedia
“Self-incompatibility,” Wikipedia