Adventitious Bud Formation from Mature Embryos of Picea chihuahuana Martínez, an Endangered Mexican Spruce Tree

Zygotic embryos of Picea chihuahuana Martinet were cultivated in vitro to determine the time of organogenic competence and to maximize adventitious bud induction. The induction medium consisted of modified B5 substrate supplemented with N-6-benzyladenine (with or without naphthalene acetic acid) or kinetin (with or without 2-4, dichLorophenoxyacetic acid) at different concentrations and induction times. The minimum induction time required for bud formation was 14 d with kinetin and 17 d with N-6-benzyladenine. After induction embryos were transferred to the proliferation medium (modified B5 substrate with 50% of its components and without growth regulators) for 30 d. The subsequent buds were transferred every 15 d to Schenk and Hildebrandt medium at half its concentration without growth regulators. The most effective treatments were 3 and 5 mg l(-1) kinetin or N-6-benzyladenine which produced five to seven buds per embryo. The largest shoots were subjected to rooting trials with pulses of different concentrations of indole butyric acid resulting in only one bud developing a root. Histological analysis revealed clusters of three to four cells that became more evident as induction time increased. Kinetin promoted the development of an organized structure prior to adventitious buds formation sooner than N-6-benzyladenine. (C) 2000 Annals of Botany Company