In vitro regeneration of Sophora toromiro from seedling explants

Embryonic axes with cotyledons, shoot-tips of embryonic axes, isolated coty ledons, as well as axillary buds and leaves from 20-year-old trees of Sopho ra toromiro, were evaluated for their capacity to trigger organogenesis and to regenerate plantlets under in vitro conditions. Embryonic shoot-tips we re the only explants capable of regenerating plants. They developed rapidly in vitro in the presence of NAA and BA while in subculture roots were indu ced at the proximal end in the presence of 0.49 muM IBA within 40-60 days. Development was completed with a subculture phase under non-sterile conditi ons using a mixture of equal parts of sterilized vermiculite/sand/soil in g rowth chambers, before final acclimation in the greenhouse. In the presence of NAA, BA and GA(3), whole embryonic axes formed multiple shoots that bra nched when grown in 2.27 or 11.35 muM TDZ in subculture. Similarly, callus was initiated at the embryo axis base, developing into several new shoots i n the presence of TDZ. Because of the relatively high shoot induction rate along the embryonic axis, this axis presents a valuable source of new juven ile explants. Growth and rhizogenesis was satisfactory only when organs fro m seed pods of the year or from the previous season were used. Experiments with isolated cotyledons produced callus only, while axillary buds and leav es did not show any responses in the presence of several growth regulators assayed. Inoculation of seedlings with various strains of rhizobia under in vitro conditions resulted in root outgrowths, but not in nodules that are typical of rhizobia infection.