In vitro rooting and early greenhouse growth of micropropagated Paulownia elongata shoots

Experiments focused on improving methods for rooting micropropagated Paulownia elongata shoots and enhancing the quality of plants grown from rooted shoots transferred to the greenhouse. Micropropagated shoots rooted on basal Murashige and Skoog medium, but inclusion of 0.2 mg/l naphthaleneacetic acid and 0.4 mg/l indole-3-butyric acid during a 10-day rooting treatment resulted in a shorter rooting time, a greater number of roots per shoot, and shorter roots that were more easily manipulated during transfer to the greenhouse. Shoots with a greater initial height had greater rooting success than short shoots. Shoots from 1.1 to 2.0 cm in height were preferable to taller shoots because: (1) less time is required to produce them, (2) their smaller leaf size makes them easier to handle, (3) they root with about the same frequency, (4) rooted shoots are more easily transferred to the greenhouse, and (5) once in the greenhouse they attain a height that is indistinguishable from shoots that were classified as very tall at the start of the rooting process. Inclusion of sucrose in the rooting medium promoted rooting as compared to shoots rooted without sucrose. Of the fertilizer treatments applied to plants newly transferred to the greenhouse, 17-17-17 (N-P-K) and 0-44-0 each applied at 1 g/l with each watering resulted in the highest portion of plant fresh mass allocated to roots (49%).