Clonal propagation of hybrid sweetgum (Liquidambar styraciflua x L-formosana) by somatic embryogenesis

Cultures were initiated from immature seeds derived from controlled pollinations between two sweet-gum species (Liquidambar styraciflua and L. formosana) cultured on two induction media supplemented with 2,4-dichlorophenoxyacetic acid. Repetitive embryogenic cultures capable of producing somatic seedlings were obtained from 2% of the 1,020 seeds cultured, representing nine crosses between L. styraciflua and L. formosana. Hybrid genotypes of somatic seedlings were confirmed by random amplified polymorphic DNA analysis and leaf morphology observations. Stomatal analysis performed on leaves from hybrid somatic seedlings and parental species revealed differences in stomata size and number per unit leaf area. Nearly 100% of the hybrid cultures re-grew and were capable of somatic embryo and seedling production following cryopreservation. Cryopreservation will allow the long-term storage of viable embryogenic cultures while hybrid trees are field-tested for identification of superior genotypes. Somatic embryogenesis appears to be a feasible approach for mass clonal propagation of hybrid sweetgum.