Adventitious rooting in olive (Olea europaea L.) cuttings: A histological evaluation

Abstract

Even when stimulated by application of exogenous growth regulators, the ability for adventitious root formation in olive remains highly genotype dependent.

When semi-hardwood cuttings are used as propagation material, its possible to find cultivars like Cobrançosa, where it is easy to achieve 70% of adventitious root formation, and cultivars like Galega vulgar, where 10% of rooting it is very difficult to exceed.

Preliminary results of a comparative histological study between the above-mentioned Olea europaea cultivars, looking for differences, both in the stem anatomy and in tissues involved in adventitious root ontogenesis, are now presented.

Concerning stem anatomy, the results achieved so far, allow to conclude that no significant differences were observed between the cultivars, both presenting a sclerenchymal ring, that may act as a mechanical barrier to the adventitious root development.

The observations made of the ontogenically active regions, showed that in Cobrançosa the new roots emerge in the vascular cambium or in the adjacent tissues, whereas in Galega vulgar the parenchyma cells of the callus are the ones involved in the appearing of roots morphogenic fields.

This significant difference observed between the kind of tissues that are involved in the process of cell des-differentiation and reacquisition of a primary meristematic condition, which is crucial to allow the formation of new root meristems, its probably correlated with the great differences observed in the rooting ability of semi-hardwood cutting of this olive cultivars.