Somatic embryogenesis from tissues of mature sweetgum trees

Clonal propagation of superior genotypes of commercially important forest trees via somatic embryogenesis has been hindered by a general inability to initiate embryogenic cultures from tissues of mature trees. We tested staminate inflorescences of sweetgum (Liquidambar styraciflua L.) as a source of cells that might be redetermined from theirdifferentiated state to an embryogenic state. Buds containing staminate inflorescences were collected from seven sweetgum clones at varying stages of elongation prior to and continuing through bud break. Inflorescence tissues were cultured on medium containing thidiazuron (TDZ) alone or in combination with 2,4-D. Although most cultures were lost to contamination or killed by disinfestation treatments, the least expanded inflorescences from buds of one clone produced eight independent embryogenic cultures following culture on 0.01--1 mg/L TDZ, either continuously or as a 1-week pulse followed by transfer to basal medium. Repetitive 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 of these converted to plantlets that were acclimatized to greenhouse conditions. These preliminary results indicate that tissues from inflorescences of mature sweetgum trees have the abilityto produce embryogenic cultures, thus providing a potential route for large-scale cloning of superior genotypes. [ABSTRACT FROM AUTHOR]