In order to improve plant survival and to achieve a better understanding of the rooting process of chestnut (Castanea sativa X C. crenata) shoot cultures Of mature origin, different rooting treatments were compared, For root induction, the basal ends of the shoots were dipped into 1 g l(-1) IBA solution for 1 min or planted for 5 days in 3 m l(-1) IBA agar medium. For root development, the induced shoots were transferred either to auxin-free agar medium (in vitro rooting) or to a peat:perlite substrate (ex vitro rooting). Rooted shoots were subsequently acclimatized. After dipping induction, the rooting percentage was higher when root development was performed in vitro (97%) than ex vitro (77%). After induction with IBA in agar medium, the root development conditions did not affect the rooting percentage (93% and 87%, respectively, for in vitro and ex vitro rooting). In the acclimatization stage, 100% survival was obtained with microplants with ex vitro-developed roots, compared to only 50% for microplants with in vitro-developed roots. After the root inductive treatments, peroxidase activity in the shoots was characterized by an initial reduction during the first 12 h, followed by a transient peak at day 1. From day 4 to day 6, peroxidase activity increased. This increase was faster in the dipped shoots, but on day 8, no difference in activity could be observed between the treatments. The sequential anatomical changes during the rooting process were similar in both root induction treatments. The first cellular divisions were observed in some of the cambial derivative cells 24 h after auxin induction and a meristemoid became individualised by days 3-4. Identifiable root primordia with a conical shape were present after 6-8 days. Roots with organized tissue systems emerged from the stein 10-12 days after the root induction treatment. (C) 1998 Elsevier Science B.V.
