Somatic embryogenesis and plant regeneration in Eucalyptus globulus Labill

Abstract.

Somatic embryogenesis was induced from juvenile explants of Eucalyptus globulus Labill. Mature zygotic embryos, isolated cotyledons, hypocotyls, leaves and stems were cultivated at 24°C in darkness on Murashige and Skoog medium supplemented with 3% (w/v) sucrose and different growth regulator combinations. Callus was formed at the surface of the explant in all tested media containing sucrose but not in those containing mannitol. Calli were transferred to the same medium without growth regulators (MSWH) after 25 days. Somatic embryogenesis was observed in callus derived from cotyledon explants and from entire mature zygotic embryos in the presence of 3–15 mg l^–1 α-naphthalene acetic acid (NAA) alone or in the presence of 1 mg l^–1 NAA combined with 1 mg l^–1 2,4-dichlorophenoxyacetic acid. Best embryogenic rates were obtained in the presence of 3–5 mg/l NAA, as approximately 30% of callus formed on these media produced somatic embryos. Exposure, for >1 week, to the highest NAA concentrations tested (15 mg l^–1) failed to induce somatic embryogenesis. Addition of 500 mg l^–1 casein hydrolysate and 500 mg l^–1 glutamine to the induction medium increased the number of abnormal somatic embryos. Conversion of somatic embryos to plantlets (21%) was obtained when they were transferred to medium free of growth-regulators.