Somatic embryogenesis in Asparagus officinalis can be an in vitro selection process leading to habituated and 2,4-D dependent embryogenic lines

Long-term embryogenic lines were repeatedly obtained from nine asparagus (A sparagus officinalis L.) genotypes by the selection of ran events, which co nsisted of the emergence of either a few somatic embryos or an embryogenic callus from a restricted area of a primary callus. In the first case, somat ic embryos emerged from 1% of calli induced with naphtaleneacetic acid and transferred to a medium without auxin. Isolated and subcultured on hormone free medium, these embryos developed habituated embryogenic lines (H lines) growing by adventive embryogenesis. In the second case, 3% of primary call i developed then subcultured on 2,4-dichlorophenoxyacetic acid (2,4-D) prod uced a new type of friable and yellowish-white callus, constituted of clust ers of globular somatic embryos which can be continuously maintained on 2,4 -D (2,4-D lines). Among 2,4-D lines, two types were identified by subcultur ing them on hormone-free medium. Half of the 2,4-D lines were habituated an d half were 2,3-D dependent. Most plants regenerated from H Lines exhibited a strong increase in embryogenic capacity compared to control plants, unli ke plants regenerated from the 2,4-D dependent lines. This increased embryo genic capacity was transmitted to the progeny as a monogenic dominant trait . H lines would therefore be issued from mutation(s) occurring in vitro, co nferring both the embryogenic and habituated phenotypes. On the contrary, i n the 2,4-D dependent lines, the embryogenic processes appeared to remain u nder exogenous auxin control and no evidence of a mutational origin could b e inferred from the behaviour of regenerated plants. (C) 2000 Editions scie ntifiques et medicales Elsevier SAS.