In Vitro Propagation of Conifers: Fidelity of the Clonal Offspring
Conifer propagation in vitro is still largely restricted to propagation of juvenile, in most cases embryonic, material. So far, the main method of regeneration has been rooting of adventitious or axillary shoots. However, this method has found little commercial application because, 1) the propagation rates are too low, 2) the cost is too high, and 3) propagation is often not true-to-type. Fortunately, methods have been developed recently to induce somatic embryogenesis in cell cultures derived from embryo expiants. Somatic embryogenesis is better suited for mass propagation than rooting of adventitious or axillary shoots. Therefore, it is anticipated that commercial propagation of juvenile conifer material will soon be possible. Mature trees are far more difficult to clone by in vitro techniques than juvenile specimens. Our work with about 30-year-old Larix decidua trees has resulted in large-scale adventitious shoot formation, but little rooting. Some of the cultures have produced yellow, slimy cell masses which were similar in appearance to embryogenic masses obtained from embryo or megagametophyte explants. They contained bundles of long cells associated with small cells, but none of these developed into recognizable embryos. The potential applications of cloning in vitro in tree improvement schemes are discussed.
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