Testing novel cytokinins for improved in vitro adventitious shoots formation and subsequent ex vitro performance in Pinus radiata

The aim of this study was to assess the effect of cytokinins not commonly used for shoot induction from zygotic embryos of Pinus radiata D. Don. The influence of in vitro shoot and root induction treatments on the subsequent ex vitro development of the regenerated plants was also tested. Embryos were cultured with benzyladenine (BA), thidiazuron (T) and two cytokinins not previously assayed in radiata pine organogenesis (meta-topolin (m-T) and zeatin (Z)) in a range of concentrations and induction periods. Shoot induction treatments were assayed in seeds from different geographical origins to obtain wider conclusions. We analysed the effect of these cytokinin treatments on in vitro rooting with different auxins ((indole-3-butyric acid (IBA) and 1-naphtalene acetic acid (NAA)) and the traditionally used mixture. After in vitro rooting, the plantlets were acclimatized and their ex vitro behaviour was evaluated. Shoot induction treatments with 1 μM BA for 2 weeks, 4.4 μM BA for 3 weeks or 1 μM Z for 3 weeks were more effective than the other treatments. An interaction between in vitro shoot and root induction treatments was observed. IBA was more efficient for plant production because the explants rooted in this auxin had better survival rates in the greenhouse.