Variability of wild olives (Olea europaea subsp. europaea var. sylvestris) analyzed by agro-morphological traits and SSR markers

The genetic diversity of wild olive trees sampled from eight different sites from two provinces of Andalusia (Cadiz and Jaen), Southern Spain, was evaluated by means of agro-morphological traits and SSR markers. The agro-morphological traits showed a high variation between genotypes and significant correlation coefficients were obtained among the values recorded in two consecutive years, 2007/08 and 2008/09 (r = 0.59–0.78). Traits such as fruit symmetry (position A), stone shape, fruit flesh/stone ratio and olive oil content on both wet and dry matter, showed the highest values of diversity and were very useful in genotype discrimination. As expected, average values obtained in wild olives for fruit size and oil content were lower than the previously reported in cultivated material. However, it is noticeable that wild trees with fruit weights (1.3 g) and olive oil percentage in dry matter (33.8%) comparable to the values found in some olive cultivars, were also found. With both DNA-based and agro-morphological descriptors, higher levels of variability were found within each site than between sites. Genetic variation observed among the wild olive germplasm at the DNA level was higher than the agro-morphological traits, indicating the efficiency of SSR markers for detecting genetic diversity among wild olive genotypes and their relationships. The lack of consistency between the relationship studies performed with molecular and morphological markers could indicate that each marker system measures different aspects of the wild olive genetic variability. Molecular data obtained by SSR markers together with morphological and agronomical characterization of olive trees confirmed the high diversity within the wild populations and their potential use for olive breeding.

► High genetic diversity of wild olives at both morpho-agronomical and molecular level.
► Morphological traits are useful both for wild olive discrimination and variability.
► SSR markers are more informative in depicting genetic relationships.
► Potential value of wild olives for breeding.