|Olive tree – Pelion, Greece
(CC by Dennis Koutou)
A new genetic study claims that the origins of olive domestication are in West Asia, more precisely at the Turkish-Syrian border (Kurdistan again?), apparently settling the doubts on whether this tree’s domestic variant may have originated either in that area, the Aegean Sea basin, Southern Iberia or North Africa, or even that many independent domestications had taken place.
G. Besnard et al., The complex history of the olive tree: from Late Quaternary diversification of Mediterranean lineages to primary domestication in the northern Levant. Proceedings of the Royal Society B, 2013. Pay per view → LINK [doi: 10.1098/rspb.2012.2833]
The location and timing of domestication of the olive tree, a key crop in Early Mediterranean societies, remain hotly debated. Here, we unravel the history of wild olives (oleasters), and then infer the primary origins of the domesticated olive. Phylogeography and Bayesian molecular dating analyses based on plastid genome profiling of 1263 oleasters and 534 cultivated genotypes reveal three main lineages of pre-Quaternary origin. Regional hotspots of plastid diversity, species distribution modelling and macrofossils support the existence of three long-term refugia; namely the Near East (including Cyprus), the Aegean area and the Strait of Gibraltar. These ancestral wild gene pools have provided the essential foundations for cultivated olive breeding. Comparison of the geographical pattern of plastid diversity between wild and cultivated olives indicates the cradle of first domestication in the northern Levant followed by dispersals across the Mediterranean basin in parallel with the expansion of civilizations and human exchanges in this part of the world.
The study was made only on chloroplast DNA, roughly equivalent to animal mtDNA, transmitted only by the “female” line (notice that olive trees, as most plants are dioic, having both sexes and also that the preferred method of agricultural reproduction today is growing new trees from stumps, i.e. cloning). However André Berville, geneticist of the French National Institute for Agricultural Research prefers to remain cautious because, in his opinion, looking only at chloroplast DNA is not enough.
“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.