Olive is one of the most important crops in the Mediterranean Basin, because of the olive oil economic value and its role in characterization of the rural landscape. The strong influence of climatic changes on the modern agriculture and the availability of a large source of genetic variability pose as crucial future challenges. Therefore, safeguarding olive genetic resources becomes fundamental, not only in cultivated forms in ex situ collections, but also in terms of wild trees in their natural habitat. In this study, 174 samples of oleaster collected in different parts of Algeria were analyzed by 16 nuclear Simple Sequence Repeats (SSRs). The analysis showed a huge genetic variability in the oleaster, and the STRUCTURE and Principal Coordinate Analyses (PCoA) highlighted clusterization of genotypes according to their geographic origin and bioclimatic conditions. Genotypes adapted to harsh climatic conditions were identified, which could be useful to enrich the panel of olive genotypes for breeding purposes and preserve genetic diversity of this species from erosion risks.

Oleaster (Olea europaea L. subsp. europaea var. sylvestris) is the ancestor of cultivated olive (Olea europaea L. subsp. europaea var. europaea) and it is spread through the whole Mediterranean Basin, showing an overlapping distribution with cultivated olive trees. Climate change and new emerging diseases are expected to severely affect the cultivations of olive in the future. Oleaster presents a higher genetic variability compared to the cultivated olive and some wild trees were found adapted to particularly harsh conditions; therefore, the role of oleaster in the future of olive cultivation may be crucial. Despite the great potential, only recently the need to deeply characterize and adequately preserve the wild olive resources drew the attention of researchers. In this review, we summarized the most important morphological and genetic studies performed on oleaster trees collected in different countries of the Mediterranean Basin. Moreover, we reviewed the strategies introduced so far to preserve and manage the oleaster germplasm collections, giving a future perspective on their role in facing the future agricultural challenges posed by climatic changes and new emerging diseases.

Algerian wild olives can represent an important resource for cultivated olive breeding, since they are characterized by great morphological variability. Moreover, they grow in different bioclimatic environments, including dry and hot climates, making the collections of wild olives a good source of abiotic stress resistance traits. Our study aimed to investigate the morphological diversity of 175 wild olive trees collected in North Algeria along with a wide range of different bioclimatic habitats for studying traits of olive accessions in relation to their different ecogeographical parameters. Wild olive trees were found in five different bioclimates areas spanning from humid to Saharan areas. They showed high variation in all traits, in particular fruit and stone weight, which expressed the highest coefficient of variation, and a high positive correlation between fruit weight/width. Cluster analysis separated the samples into two groups mostly based on fruit and stone size, while no relationship was observed with the area of sampling. Only the Saharan samples showed significantly different foliar and fruit characteristics compared to samples from other bioclimatic areas.