Genetic Diversity and Conservation of Olive Genetic Resources

Abstract

The olive (Olea europaea subsp. europaea) is indigenous to the Mediterranean Basin and is the most economically important oil tree crop in temperate areas. Olive cultivars (Olea europaea subsp. europaea var. sativa) have been empirically selected and vegetatively propagated in all the traditional olive-growing countries. However, the domestication history of the olive and its relationship with its wild ancestor (Olea europaea subsp. europaea var. sylvestris) remain puzzling. The knowledge of the relationship between cultivars and wild olives is critically important for conservation purposes, for breeding programs, for the design of genome association studies, and to untangle the population history. In this chapter, we examine the characterization of olive genetic resources (wild and cultivated) in the main olive-growing regions of Spain using microsatellite (SSR) markers. We observed significant differentiation between the cultivars from south and northeast Spain, which possibly indicate independent selection processes. In addition, our results revealed differential relationships and admixture events between the wild and cultivated olives depending on their region of origin. Finally, we describe how the new olive-growing systems, which are more intensive and mechanically harvested, are leading to a reduction in the number of cultivars used in new plantations. Coordinated efforts involving the application of ex situ and in situ conservation approaches are needed to evaluate and preserve the wealth of genetic legacy present in both the wild and cultivated olive. These actions are urgent, given the rapid expansion of new olive plantations and the severe effects of climate change that are predicted for the Mediterranean Basin.