Plant regeneration from embryogenic cultures initiated from mature loblolly pine zygotic embryos

Summary Mature zygotic embryos of eight (open-pollinated) families of loblolly pine (Pinus taeda L.) were cultured on eight different basal salt formulations, each supplemented with 36.2 μM 2,4-dichlorophenoxyacetic acid, 17.8 μM 6-benzyladenine, 18.6 μM kinetin, 500 mg l⁻¹ casein hydrolysate, and 500 mg l⁻¹ l-glutamine for 9 wk; embryogenic tissue was formed on cotyledons, hypocotyls, and radieles of mature zygotic embryos. Callus was subcultured on the callus proliferation medium, the same as the induction medium but with one-fifth concentration of auxin and cytokinin for 9 wk. On this medium a white to translucent, glossy, mucilaginous embryogenic callus containing embryogenic suspensor masses (ESMs) was obtained. The highest frequency of explants forming embryogenic tissue, 17%, occurred on a modified Murashige and Skoog salts basal medium containing the concentration of KNO₃, Ca(NO₃)₂·4H₂O, NH₄NO₃, KCl, ZnSO₄·7H₂O, and MnSO₄·H₂O, 720, 1900, 400, 250, 25.8, and 25.35 mg l⁻¹, respectively. Embryogenic suspension cultures were established by culturing embryogenic callus in liquid callus proliferation medium. Liquid cultures containing ESMs were transferred to medium containing abscisic acid, polyethylene glycols, and activated charcoal for stimulating the production of cotyledonary somatic embryos. Mature somatic embryos germinated for 4–12 wk on medium containing indole-butyric acid, gibberellic acid, 6-benzyladenine, activated charcoal, and reduced sucrose concentration (15 g l⁻¹). Two hundred and ninety-one regenerated plantlets were transferred to a perlite:peatmoss:vermiculite (1∶1∶1) mixture, then the plants were transplanted to soil in the earth, and 73 plantlets survived in the field.