Olive Tree Genetic Resources Characterization Through Molecular Markers

The olive is one of the most ancient cultivated fruit trees. Olive cultivation has a very long history which started from the Third Millennium BC (Loukas & Krimbas, 1983) in the Eastern region of the Mediterranean sea and spread later around the basin following land and maritime routes to Italy, Spain, North Africa and France. Nowadays there are about 805 million of olive trees, 98% of which are grown in the Mediterranean countries (Tsitsipis et al., 2009). The foremost consuming countries are also the main olive oil producers. According to Food and Agriculture Organization of the United Nations, Mediterranean countries produce more than 90% of world olives, and the biggest olive producers are Spain, Italy, Greece, Turkey, Tunisia, Morocco, Syria, and Portugal (FAO, 2008). Other consuming countries are the United States, Canada, Australia and Japan (Hatzopoulos et al., 2002; Pinelli et al., 2003). Though the olive oil consumption has been mainly constricted to Mediterranean countries, actually it has been extended to other areas due to its health beneficial proprieties (Bracci et al., 2011). Over the centuries, olive trees were propagated mainly vegetatively and were selected based on olive quantitative and qualitative traits. However, this procedure did not exclude the problematic of natural crossing between the newly introduced cultivars and the local germplasm and somatic mutation events, and genetic variability among the olive tree collections has been reported by several authors (Angiolillo et al., 1999; Bautista et al., 2003; Belaj et al., 2002, 2003, 2004, 2006; Cordeiro et al., 2008; Gemas et al., 2000; Gomes et al., 2008, 2009; Martins-Lopes et al., 2007, 2009; Sefc et al., 2000). In addition, the olive tree is allogamous, easily generating crosses between cultivars which give rise to high genetic variability between and within cultivars (Mekuria et al., 1999; Ouazzani et al., 1996; Zohary, 1994).