SOMATIC EMBRYOGENESIS FROM TISSUES OF MATURE SWEETGUM TREES

Clonal propagation of superior genotypes of commercially important for est trees via somatic embryogenesis has been hindered by a general ina bility to initiate embryogenic cultures from tissues of mature trees. We tested staminate inflorescences of sweetgum (Liquidambar styraciflu a L.) as a source of cells that might be redetermined from their diffe rentiated state to an embryogenic state. Buds containing staminate inf lorescences were collected from seven sweetgum clones at varying stage s of elongation prior to and continuing through bud break. Inflorescen ce tissues were cultured on medium containing thidiazuron (TDZ) alone or in combination with 2,4-D. Although most cultures were lost to cont amination or killed by disinfestation treatments, the least expanded i nflorescences from buds of one clone produced eight independent embryo genic cultures following culture on 0.01-1, mg/L TDZ, either continuou sly or as a I-week pulse followed by transfer to basal medium. Repetit ive embryogenesis continued on medium containing 0.01 mg/L TDZ. While most embryos were malformed, embryos from two of the clones germinated on basal medium lacking casein hydrolysate, and germinants from one o f these converted to plantlets that were acclimatized to greenhouse co nditions. These preliminary results indicate that tissues from inflore scences of mature sweetgum trees have the ability to produce embryogen ic cultures, thus providing a potential route for large-scale cloning of superior genotypes.