Effect of synthetic auxins on in vitro and ex vitro bromeliad rooting

Abstract

The tissue culture can contribute to the propagation of several economic species, such as the bromeliads. This research aimed at evaluating the auxins type and concentration in the in vitro and ex vitro rhizogenesis of Neoregelia concentrica bromeliad. N. concentrica shoots were induced in a growth medium with 15.0 µM of 6-benzylaminopurine, for 80 days, followed by sub-cultivation in phytoregulator-free medium, for 45 days. In the in vitro rhizogenesis, the shoots grew in a medium supplemented with indole-3-butyric acid (IBA) or naphthalene-acetic acid (NAA), at the concentrations of 0.0 µM, 1.0 µM, 2.0 µM, 3.0 µM and 4.0 µM. In the ex vitro rhizogenesis, the bases of shoots were immersed, for 60 minutes, in IBA or NAA solutions, at the concentrations of 0.0 µM, 5.0 µM, 10.0 µM and 15.0 µM. After immersion, the shoots were planted in plastic trays with vermiculite. At the end of each rhizogenesis method, the phytotechnical parameters analysis was carried out. For the in vitro rhizogenesis, a higher number of roots were observed when the shoots were cultivated in concentrations higher than 1.0 µM of NAA, when compared to the IBA. However, the rooting rate differed only at 30 days after the in vitro growth, with a higher root induction in the shoots grown with NAA. At 60 days, the rooting rate was higher than 90% and statistically similar in all treatments. In the ex vitro rhizogenesis, a better formation of the rooting system was observed when 5.0 µM of IBA was applied, with higher rooting averages and number of roots.