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

Abstract

Zygotic embryos of Picea chihuahuana Martı́nez 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 N6-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 14d with kinetin and 17d with N6-benzyladenine. After induction embryos were transferred to the proliferation medium (modified B5 substrate with 50% of its components and without growth regulators) for 30d. The subsequent buds were transferred every 15d to Schenk and Hildebrandt medium at half its concentration without growth regulators. The most effective treatments were 3 and 5mgl−1kinetin or N6-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 N6-benzyladenine.