Plant growth and root system morphology of Olea europea L. rooted cuttings as influenced by arbuscular mycorrhizas

The effects of arbuscular mycorrhizal (AM) fungi on plant development and root system morphology of different cultivars of Olea europaea were investigated. Rooted cuttings of olive cvs Frantoio, Moraiolo and Leccino at the beginning of the rooting phase, were inoculated with the AM endophyte Glomus mosseae. After six monthly growth increments, the percentage of root colonization and the root system morphology of the rooted cuttings were evaluated. AM inoculation enhanced growth of olive plants compared with the controls, inducing a different behaviour of the three olive cultivars colonized by G. mosseae. The fungal symbiont mainly increased the growth of the rooted cuttings of 'Moraiolo' and 'Frantoio', whereas 'Leccino' plants showed no significant differences from the controls. Staining of root samples of the cuttings indicated differences in the percentage of AM root colonization depending on cultivar. 'Moraiolo' root systems showed significantly less root length infected by Glomus mosseae compared with the other two cultivars. The morphometric analysis of olive roots demonstrated that colonization by AM fungi can significantly alter root system morphology. Colonization increased the intensity of branching on lateral orders in all cultivars and greatly increased the proportion of higher order laterals in the root system. The overall effect of mycorrhizas was, consequently, to increase lateral root frequency; giving rise to a more branched root system. Moreover the results show that such an increase in branching could be due in part to a better nutrition of mycorrhizal plants whereas mycorrhizal colonization and cultivar type greatly influenced the rooting pattern. These results show that mycorrhizal symbiosis can not only result in a significant increase in plant growth but can also alter olive root system morphology, positively affecting the establishment of plantlets.