Origins of olive tree revealed

The olive was first domesticated in the Eastern Mediterranean between 8,000 and 6,000 years ago, according to new research.

Olives, like the Salonika variety pictured here, were likely first domesticated in the Levant around 6,000 years ago, new research suggests [Credit: Jean Paul Roger]

The findings, published today (Feb. 5) 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.

"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." 

From biblical times, the olive tree has served as a symbol of sacredness, peace and unity. Archaeologists have unearthed olive pits at sites dating to about 8,000 years old. And dating as far back as 6,000 years ago, archaeologists find evidence of olive oil production in Carmel, Israel, Besnard said.

Yet exactly where the olive was first cultivated has been hotly debated. 

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, he 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.

But to get a true sense of how the olive tree emerged, the researchers shouldn't just look at chloroplast DNA, said André Bervillé, a geneticist at the French National Institute for Agricultural Research, who was not involved in the study. Nuclear DNA, which is carried in the pollen, should also be analyzed, Bervillé told LiveScience.

"Pollen from the olive tree is wind-transported, so it can migrate long distances" he said.

Combining both types of DNA would allow researchers to understand both how local olive tree cultivation occurred and how more long-distance changes occurred, he said.

Author: Tia Ghose | Source: LiveScience [February 05, 2013]