Interaction of explant type and indole-3-butyric acid during rooting in vitro in a range of difficult and easy-to-root woody plants

Axillary shoots of woody species that were easy-to-root (Forsythia x intermedia, Betula pendula and juvenile Quercus robur) and difficult-to-root (Syringa vulgaris, 'intermediate' phase Q. robur and Daphne cneorum), were used to obtain various explant types (Entire, Detipped, Nodal or Internodal) that differed in their rooting responses. When apices or axillary buds were removed from explants, rooting levels decreased, and the time to root and loss of synchrony of rooting increased. Exogenous indole-3-butyric acid generally overcame these trends, and was essential for root induction in `intermediate' Quercus and Daphne, and in all internode explants. The interaction between explant type and indole-3-butyric acid suggests a role for endogenous factors in the initiation and development of rooting. The internode explant has potential as a tool for further physiological and biochemical studies, as it is auxin-dependent and provides rooting-permissive or non-permissive states.