Effects of auxins on organogenesis and somatic embryogenesis from juvenile explants of 'Eucalyptus erythronema', E. 'stricklandii', and two inter-specific hybrids

Organogenesis and somatic embryogenesis were investigated in apex and cotyledon explants of 'Eucalyptus erythronema, E. strick landii' and their inter-specific hybrids 'Eucalyptus erythronema' X E. 'stricklandii cv'. 'Urrbrae Gem' and 'Hybrid 2.5', following exposure to 1 mg 1-¹ naphthaleneacetic acid (NAA) plus 1 mg 1-¹ 2,4dichlorophenoxyacetic acid (2,4-0), or 3, 5 or 15 mg 1-¹ NAA alone. Somatic embryogenesis was not observed macroscopically; however, structures characteristic of globular somatic embryos or root primordia were observed using light microscopy of apex explants of 'Urrbrae Gem' seedlings after 14 d on Murashige and Skoog (1962) (MS) medium supplemented with 3 mg 1-¹ NAA. Root development was associated with explant vascular tissue and observed in all plant growth regulator (PGR) treatments, but was less on explants treated with 1 mg 1-¹ NAA plus 1 mg 1-¹ 2,4-0 than in all NAA-alone treatments. Shoot development was observed on apex explants after sub-culture on PGR-free medium, but was less after treatment with 1 mg 1-¹ NAA plus 1 mg 1-¹ 2,4-0 compared to all NAA-on1y treatments. Roots and sho ts developed simultaneously on apex explants after culture for 1 week on MS medium supplemented with 15 mg 1-¹NAA.