Olive domestication from structure of oleasters and cultivars using nuclear RAPDs and mitochondrial RFLPs

Abstract

RAPD profiles of 121 olive cultivars were compared to those of 20 natural oleaster populations from eastern and western parts of the Mediterranean Basin. Considering the proximities of RAPD profiles between cultivars and eastern or western oleaster populations, clear differences appeared between groups of cultivars. Cultivars from Israel, Turkey, Syria, Greece and Sicily were, with very few exceptions, close to the eastern group of oleasters; in contrast, clones from Continental Italy, Continental France, Corsica, Spain and the Maghreb were closer to the western group. This genetic structure is coherent with a local selection of cultivars all around the Mediterranean Basin. The cultivars were also characterised for their mitochondrial cytotype. This information led to the conclusion that a great majority (103 of 121) of the cultivars originated by maternal descent from the eastern populations as they carry the mitotypes ME1 or ME2. However, the selection process, which involved hybridisation by pollen from local populations, could have led to an Rapd profile closer to western than to eastern natural populations. Furthermore, the other cultivars with the western mitotypes MOM or MCK generally kept a nuclear Rapd profile close to the profile of western natural populations. Consequently, they could result from exclusively local material (as for Corsica). Cultivars displaying such mitotypes could also have been selected in hybrids or introgressed genotypes between western local oleasters and the introduced eastern varieties used as male parents, restoring an eastern RAPD type. Therefore, the process of olive domestication appeared as disymmetrical: The western Mediterranean is probably a zone where olive trees from the East, once introduced, have been hybridised and back-crossed with the indigenous olives.