Micropropagation of juvenile tissue of Eucalyptus erythronema x Eucalyptus stricklandii cv. 'Urrbrae Gem'

Micropropagation via enhanced axillary shoot proliferation was investigated in the ornamental Eucalyptus cv. 'Urrbrae Gem' using in vitro germinated seedlings and was successfully achieved using woody plant medium (WPM) supplemented with 2.2 mu M benzylaminopurine, 1.0 mu M alpha-naphthaleneacetic acid, and 1.5 mu M gibberellic acid (GA(3)), gelled with 5 g l(-1) Phytagel((R)). Shoot proliferation was greater on WPM and QL media with GA(3) compared to B5, AP, and TK media with or without GA(3). GA(3) was required for shoot elongation as the internodes were otherwise very short and unsuitable for multiplication or root initiation. Root initiation was improved using (1/2)WPM supplemented with 20 mu M indole-3-butyric acid (IBA) over a 7 d pulse, followed by subculture to IBA-free medium, compared to placing shoots on low levels of IBA for 4-6 wk. Plantlets were successfully hardened off to the natural environment via a fogger at 67% relative humidity at 21 degrees C for 3 d and continued to thrive as potted plants. This is the first report of successful micropropagation in an ornamental eucalypt (subgenus Symphyomyrtus) from seedling explants.