Effect of auxins on axillary and de novo shoot regeneration from in vitro shoot cultures derived from forced epicormic buds of teak (Tectona grandis L.)

In this presentation, we report on de novo and axillary shoot regeneration and rooting of shoots maintained over a long term, from cultures of Tectona grandis L. Shoot-tips of teak shoots forced from epicormic buds were used as the starting material for axenic shoot-culture establishment. Long term maintenance of such axenic shoot cultures was carried out by regular sub-culturing on MS media supplemented with N⁶-benzyleadenine (BA, 8.8 μmol·L^-1) and indole-3-butyric acid (IBA, 2 μmol·L^-1) for 24 months. Vigorously growing shoot tips (2-3 cm long) were inoculated on the MS basal medium supplemented with different concentrations (0, 1, 2, 4, 6, 8 or 10 μmol·L^-1) of either IBA or α-naphthaleneacetic acid (NAA) for rooting. Axillary and de novo shoots were developed from axillary and cut basal ends of shoots, respectively. Shoots growing on auxins were further sub-cultured (every 15 days) and maintained for 45 days. The greatest number of de novo (5.06) as well as axillary shoots (2.85) was observed on the MS medium supplemented with 10 μmol·L^-1 NAA or 8 μmol·L^-1 IBA, respectively, after 45 days. The combinations of both IBA (μmol·L^-1) + NAA (μmol·L^-1) were tested at different concentrations (4 + 4, 6 + 6, 8 + 8) supplemented to a half strength MS basal medium with 0.1% activated charcoal for rooting of decapitated and non-decapitated de novo and axillary shoots. Rooting from non-decapitated de novo shoots was highest (93.33%) with a mean number of roots of 4.61 on this medium, supplemented with 6 μmol·L^-1 IBA + 6 μmol·L^-1 NAA, after 36 days of initial culture. Individual auxin, however, was not effective for root induction. Rooted shoots were acclimatized in a green house and after four weeks plantlets were transferred to the field.