Study, collection and characterization of oleaster genetic resources

Wild olive populations spread in many of the Mediterranean regions. In Sardinia Island, however, the oleaster (Olea europaea var. sylvestris) provides a reserve of genetic resources, both as a component of Mediterranean maquis and in the form of very old trees. Sometimes the two characters are combined in very old woods of oleaster which represent an original expression of the plant potential. With the aim to observe the natural colonization of oleaster in Sardinia a research program started in 1995. Some mother plant for a preliminary in situ description was subsequently selected, and shoots were sampled in order to find a morphologic and biometric description. Fruit bearing shoots were also sampled to perform agamic (softwood cuttings) and gamic (mature seeds) propagation of accessions. About one hundred accessions were selected, described and tested for propagation. As a result of this field observation, an ex situ collection of 30 accessions, mostly agamically propagated, was planted in 1998 in the experimental farm of the University of Sassari located in Oristano (Central Western Sardinia). The repository was the source of new data to complete the primary characterization of the accessions, like leaf, fruit and inflorescence morphology and biometry. More information was also obtained on flower biology, phenology and some agronomically relevant characters, like fruit composition. The dynamic of cambium activity, continuously observed for some years showed a significant stop of the tree growth between January and February and the lack of a similar stop during the summer. The wild population was analyzed for genotype characteristics, as compared with the regional olive germplasm by mean of different kinds of molecular markers (AFLP and SSR) and also compared with other wild population from other Mediterranean regions. These investigations have not demonstrated a relationship between wild population and olive germplasm in Sardinia and even if the introgression of cultivated genotypes in the wild population is realistically possible, the wild population, selected following our preliminary targets, showed a relative distance from the cultivated olive.