Induction of somatic embryogenesis from young, fully expanded leaves of chilli pepper (Capsicum annuum L.): effect of leaf position, illumination andexplant pretreatment with high cytokinin concentrations

The effect of the explant position on the donor plant, illumination and exp lant pretreatment with high cytokinin concentrations on the induction, prol iferation and development of somatic embryos from young, fully expanded lea ves of chilli pepper (Capsicum annuum L.) was investigated. Explants were c ultured either directly on a solid Murashige and Skoog medium supplemented with 9 mu M 2,4-dichlorophenoxyacetic acid + 12.9 mu M 6-benzyladenine or i ncubated for 24 h in a liquid MS medium containing the cytokinin at a tenfo ld concentration (129 mu M) and then transferred to the solid MS medium. Gl obular embryo proliferation depended on the leaf position on the donor plan t: fewer embryos were derived from the third leaf (counting from the base o f the shoot) than from the first two leaves. The initial pretreatment of pe pper explants with increased 6-benzyladenine concentrations significantly r educed the overall proliferation bf somatic embryos without affecting the p ercentage of globular embryos which further developed into the torpedo-shap e stage and germinated. Depending on the leaf position, somatic embryo indu ction was significantly affected by the initial culture incubation under il lumination or in darkness. Heart- and torpedo-shaped embryos could be obser ved only on callus pieces initially incubated for 3 weeks in darkness. (C) 2000 Elsevier Science B.V. All rights reserved.