Micropropagation of Clerodendrum L. species: a review

Species within the Clerodendrum genus possess well-established pharmacological and medicinal properties. These emanate from the presence of many unique bioactive secondary metabolites. Eight Clerodendrum species (C. anomalum, C. calcicola, C. denticulatum, C. galeatum, C. leucophloeum, C. lutambense, C. eupatorioides, and C. aculeatum) are listed on the International Union of Conservation of Nature Red Data List. Micropropagation offers an opportunity for the conservation and large-scale propagation of elite genotypes and is a widely used technique for the conservation of threatened medicinal plants, including Clerodendrum species. This review highlights the advances that have been made thus far in the in vitro tissue culture of members of the Clerodendrum genus. Most of the efforts made to date have focussed on basic in vitro growth or regeneration, primarily from seeds, nodes, and leaves, either from an ex vitro or an in vitro source. Following a wide range of disinfection procedures that depend on the source and age of the explant, most studies employed Murashige and Skoog basal medium in a 12- to 16-h photoperiod. The most effective cytokinin for the induction of shoots was N6-benzyladenine. Although plantlet acclimatization to field conditions was widely reported, it was often poorly quantified. Based on this base of information, applied aspects such as genetic engineering, mutation breeding, the production of haploid and double-haploid lines, protoplast fusion, embryo rescue, in vitro production of secondary metabolite acquisition through hairy roots or bioreactors, somaclonal variation, and cryopreservation still need to be developed and explored.