Regeneration of Transgenic Cassava From Transformed Embryogenic Tissues

Production of transgenic plants is gradually becoming routine in cassava biotechnology. Green cotyledons of maturing somatic embryos (somatic cotyledons for short) and friable embryogenic suspensions (FES) are the target tissues for transformation by Agrobacterium or biolistics. Putative transgenic shoots develop from transformed somatic cotyledons via shoot organogenesis or from FES via somatic embryogenesis under selection. Maturation of transgenic somatic embryos is induced by transfer to maturation medium with reduced concentrations of selective agents. Mature somatic embryos can also develop directly from FES cells under selection. Transgenic plants are regenerated by the elongation of transgenic shootlets from organogenesis experiments and by the germination of or shoot development from transgenic mature embryos cultured without selection. β-Glucuronidase (GUS) assays and rooting tests can be used to screen for escapes from selection, which improves the regeneration rate of truly transgenic plants.