TIBA affects the induction of direct somatic embryogenesis from leaf explants of Oncidium

To study the effect of auxin on direct somatic embryogenesis from leaf cultures of Oncidium 'Gower Ramsey', 1-cm-long explants have been cultured in vitro testing IAA, 2,4-D, quercetin, TIBA and PCIB. On a modified MS medium devoid of plant growth regulators, leaf cells of three regions (leaf tips, adaxial sides and cut ends) formed somatic embryos. After 8 weeks in culture, the frequencies of embryo-forming explants were 55, 52.5 and 30% on leaf tips, adaxial sides and cut ends, respectively, and the numbers of embryos per dish was 89.3. Except for TIBA, other growth regulators (IAA, 2,4-D, quercetin, PCIB) and their combinations tested, all retarded direct embryo formation. In the presence of 0.1 and 0.5 muM TIBA, leaf tip, adaxial sides and cuts end of explants gave almost the same embryogenic response as the control. However, 10 and 27.5% of explants were induced to form embryos from abaxial sides, and these explants did not form embryos on cut ends. In addition, after 8 weeks in culture, TIBA at 0.5 muM highly promoted the mean numbers of embryos per dish to 134.2.