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In vitro propagation of Leucadendron laureolum x L. salignum cv. Safari Sunset: ultrastructural and anatomical studies of regenerated plantlets

Leucadendron laureolum L. salignum cv. Safari Sunset is a hybrid of the Proteaceae family and is economically important as an ornamental crop. The economic interest of this species to Madeira Island and the difficulties of cloning it by conventional methods led us to test in vitro techniques to achieve propagation. Axillary shoot proliferation was carried out on a modified MS medium containing ascorbic acid (15 mg l-1) and 2% sucrose. Several combinations of growth regulators were used. Best results were obtained when 2.0 mg l-1 BA and 2.0 mg l-1 GA3 were tested. Under these conditions, an average of seven shoots were produced per explant and shoot length reached 19 mm. Rooting was more efficient when the basal ends of the in vitro propagated shoots were dipped in an IBA solution (1.0 g l-1) for five minutes, followed by their transfer into a jellified MS basal medium with the nutrients reduced at half strength or to “Sorbarod” plugs saturated with the same liquid medium. Under these conditions about 83% of the shoots showed root formation. Anatomical and ultrastructural studies showed some modifications occurring in leaves of micropropagated plants. These modifications included a thin cuticle formation and abnormalities of the vascular bundles that could be responsible for the extremely low levels of success observed during plant acclimatization.