Axillary bud proliferation and somatic embryogenesis in american yellowwood [Cladrastis lutea (Michx.) K. Koch]

The potential for in vitro propagation of Cladrastis lutea (Michx) K. Koch [American yellowwood] by axillary bud proliferation and somatic embryogenesis was investigated. Axillary buds were removed from elongating branchlets during the first week in April 1989 and aseptically cultured on modified Murashige and Skoog (MS) medium amended with either 0.5, 1.0, 3.0 or 5.0 mg*liter^-1 6-benzyladenine (BA). The numbers of shoots and buds were recorded at four week intervals for 24 weeks. The average length of harvested shoots decreased with increasing BA concentrations. Conversely, the average number of buds per explant increased with higher BA levels. Axillary buds cultured on medium supplemented with 1.0 mg*liter^-1 BA produced the most consistent number of elongated shoots and buds over the six month culture period. Elongated shoots produced on any of the BA treatments were excised and transferred to rooting medium. Excised shoots could be rooted only when cultured in the dark on half-strength MS medium supplemented with 1.0 mg*liter^-1indole-3-butyric acid (IBA).

The somatic embryonic potential of yellowwood was investigated by aseptically culturing 4-10 week post-anthesis ovules at weekly intervals. Zygotic embryos were excised and placed on Shenck and Hildebrandt (SH) medium supplemented with either 1.0, 2.0, 3.0 or 5.0 mg*liter^-1 2, 4-D. Explants were transferred after 2 and 3 weeks to SH medium amended with 5.0 mg*liter^-1 1-naphthaleneacetic acid (NAA). Somatic embryos were initiated on all treatments and usually formed as pairs at the proximal end of the cotyledonary tissue. The greatest embryonic response occurred from 6-8 weeks post-anthesis. Somatic embryos typically had fascinated cotyledons but were capable of producing a radicle when transferred to half-strength SH medium lacking hormones. Whole plants were regenerated from 3 embryos and established in soil.