Effects of diphenylurea derivatives on adventitious rooting

Adventitious root formation is a key step in vegetative propagation of plants, one of the most efficient methods to multiply plants in vivo or in vitro. Endogenous auxin (namely indole 3 acetic acid, IAA) has been established as natural inducer of root formation, and its capacity to induce roots when exogenously applied has also been rapidly recognised. However, in the case of woody plants there is often a physiological inability to produce adventitious roots even after external supplementation of auxins, either natural or synthetic. Despite the huge commercial interest and the large number of attempts, auxin alone has proved to be not sufficient to induce root formation in so called difficult to root species. Different strategies have therefore been implemented with a view to improving adventitious rooting: treatment with any kind of plant growth regulators; supplementation of non hormonal compounds such as polyamines, phenolic compounds, thiol compounds; use of Agrobacterium rhizogenes as root inducing bacterium. Considering broad interest in the area of nonhormonal bioactive compound supplementation, in this chapter we summarize the effects of some diphenylurea derivatives as “rooting adjuvants”, since they markedly enhance rooting when applied alone or in combination with auxins.