Reliable plantlet formation from embryos and seedling shoot tips of radiata pine

A method has been devised for the reliable production of plantlets from embryos and seedling shoot tips of Pinus radiata D.Don (radiata pine). Buds were induced on an agar or liquid Schenk and Hildebrandt (SH) medium containing 5.0 mg/l benzylaminopurine (BAP). Except for some abnormal buds, the buds grew into elongated shoots on an agar SH medium without cytokinin. The transfer of shoots from a SH medium to a Gresshoff and Doy (GD) medium was found to be an important pretreatment which increased the survival of the shoots when they were placed in a peat and pumice mix for root formation. Elongated shoots were induced to form roots under non-sterile conditions in a humid environment with occasional misting. An intervening 5-day treatment of shoots in an agar medium containing 2.0 mg/l indolebutyric acid (IBA) and 0.5 mg/l napthaleneacetic acid (NAA) significantly increased the percentage of shoots forming roots and the number of roots formed per shoot over control shoots placed directly in the peat:pumice mix. An enhanced level of CO₂ during root formation had no effect on the time of root formation or on the percentage of shoots forming roots. These results concerning the elongation, growth and rooting of adventitious shoots are now being applied to the development of very large numbers of plantlets starting from cotyledons from partially germinated seeds.