Adventitious bud formation from mature embryos of Picea chihuahuana Martinez, an endangered Mexican spruce tree

Zygotic embryos of Picea chihuahuana Martinet were cultivated in vitro to d etermine the time of organogenic competence and to maximize adventitious bu d induction. The induction medium consisted of modified B5 substrate supple mented with N-6-benzyladenine (with or without naphthalene acetic acid) or kinetin (with or without 2-4, dichlorophenoxyacetic acid) at different conc entrations and induction times. The minimum induction time required for bud formation was 14 d with kinetin and 17 d with N-6-benzyladenine. After ind uction embryos were transferred to the proliferation medium (modified B5 su bstrate 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 effect ive treatments were 3 and 5 mg l(-1) kinetin or N-6-benzyladenine which pro duced five to seven buds per embryo. The largest shoots were subjected to r ooting trials with pulses of different concentrations of indole butyric aci d resulting in only one bud developing a root. Histological analysis reveal ed clusters of three to four cells that became more evident as induction ti me increased. Kinetin promoted the development of an organized structure pr ior to adventitious buds formation sooner than N-6-benzyladenine. (C) 2000 Annals of Botany Company.