Protocols for efficient repetitive and secondary somatic embryogenesis in Helianthus maximiliani (Schrader)

Indirect somatic embryogenesis was induced on leaf explants of greenhouse-g rown Helianthus maximiliani plants. Leaves of the regenerated plants were u sed as starting explants for the induction of direct somatic embryogenesis. Another cycle of somatic embryogenesis was induced on the leaves of regene rated plants. In both cases, leaf explants were cultured on media containin g different auxin/cytokinin ratios. The auxin/cytokinin ratio had an influe nce on the intensity of embryo formation, germination and the capability to regenerate plants. Somatic embryogenesis was generally more intensive on t he medium with lower concentrations of 6-benzylamino-purine. Further, the p ercentage of regenerated plants was higher when embryos were induced on hig h-cytokinin, low-auxin medium. Secondary somatic embryogenesis was induced on embryos by culture in liquid hormone-free medium. Similar to direct embr yogenesis the efficiency of secondary embryogenesis depended on the medium used for the induction of the primary embryos. In contrast to the mostly lo w frequencies of conversion of secondary embryos into plants that has been observed in other species, the percentage of regenerated plants from second ary embryos of H. maximiliani was quite high, although slightly lower than that obtained in primary embryos.