Azospirillum baldaniorum Sp245 Induces Anatomical Changes in Cuttings of Olive (Olea europaea L., cultivar Leccino): Preliminary Results

The purpose of the research was to assess the potential effectiveness of Azospirillum baldaniorum Sp245 in stimulating the induction processes related to adventitious root formation. In this short communication, we present the preliminary results obtained for the first time for the Leccino olive cultivar (Olea europaea L.). Semi-hardwood cuttings were collected at different sampling times (autumn, winter, and spring) and subjected to root-inductive treatments with Azospirillum baldaniorum strain Sp245 (AZO) and indole-3-butyric acid (IBA), the most employed synthetic auxin used in nursery production of olive plants. Moreover, two growing substrates, perlite (an inorganic medium) and Elepot(R) (a blend of peat, coconut fiber, and perlite) were tested. Histological assays were carried out to identify the main cellular changes leading to adventitious root formation. The highest rates of cuttings showing more advanced stages of rooting inductive signals were observed with the spring sample. The events observed after AZO treatments were comparable to those observed with IBA, which were mainly associated with the Elepot(R) growing substrate. The positive responses of semi-hardwood cuttings of Leccino cultivar to AZO could provide the possibility of replacing IBA and develop perspectives in a context of organic nursery systems where alternative compounds, able to improve the rooting rate of cuttings, could substitute the non-permitted synthetic rooting agents. AZO induced significant cellular activities and could be considered a valid alternative rooting agent.