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Genetic Diversity and Relationship among Wild Olive Populations

Wild olives (Olea europaea subsp. europaea var. sylvestris) include true oleasters (corresponding to the wild forms present in natural areas) and feral forms, which may be seedlings of the cultivated clones or result from hybridisation between the true oleasters and olive cultivars. The knowledge of the genetic variability of wild olive populations and the study of their relationships may be of great interest for their possible use as a new source of variability in breeding programmes. For that purpose, eight microsatellite markers have been used to study the genetic variation within and between 11 wild olive populations from Southern and North-Eastern Spain and mainland and insular Italy. Our study uncovered abundant allelic variation over eight loci with an average of 18.5 per locus alleles and high values of observed and expected heterozygosity (mean values of 0.717 and 0.843 respectively). Although most of the genetic diversity was attributable to differences among individuals within populations (91.8%), significant phi-values among populations suggested the existence of genotypic differentiation. The analysis of STRUCTURE allowed the detection of four different gene pools: OS, OI, F1 and F2 despite the overall low interpopulation differentiation of this tree species. The gene pools OS and OI predominantly found in southern Spain and Italian islands, respectively may correspond to genuine wild olive germplasm. The gene pools F1 and F2 detected in North-Eastern regions of Spain and in continental Italy likely represent feral gene pools. The existence of four gene pools and the evidence of differences between the genuinely wild olive germplasm and the feral forms were in overall concordance with the Fitch-Margoliash tree based on Nei's genetic distance.

wild olives; oleasters; feral forms; microsatellites; genetic structure

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