Rooting treatment and the ex vitrum performance of micropropagated plants

The leaves of tissue-cultured plants have a very poor water retention capacity (WRC), principally due to malfunctioning stomata. When microcuttings are rooted in vitro, these roots replenish water that is excessively lost after transplanting because of the poor WRC. The ex vitro growth performance of in vitro rooted apple microcuttings was correlated with the number and the length of roots at transplanting. The optimal auxin for in vitro rooting of apple microcuttings was indoleacetic acid, and not naphthaleneacetic or indolebutyric acid. The role of ethylene in in vitro rooting was complex. It enhanced the responsiveness to the rhizogenic action of auxin and was required in root hair formation. On the other hand, ethylene inhibited root meristem formation and root elongation, and induced leaf senescence.