Micropropagation and genetic transformation of Spanish Cedar (Cedrela odorata L.): A Review

Abstract

Cedrela odorata L. (Meliaceae) is a timber tree of high economic value. Currently, this species faces serious problems due to selective cutting and environmental degradation, which together have contributed to the decline of C. odorata populations. Establishment of C. odorata commercial plantations on a large scale could alleviate the pressure on natural populations of this species. However, C. odorata plantations are limited due to the susceptibility to the mahogany shoot borer (Hypsipyla grandella Zeller). H. grandella destroys the apical meristems and shoots causing malformations in the stem and subsequently the death of the plant. Genetic improvement of C. odorata by conventional methods is a slow process due to several factors associated with its biology: a long life cycle, recalcitrant seeds, large tree size, low genetic diversity and sexual incompatibility. Therefore, in vitro propagation is the best option for clonal multiplication and assistance to breeding programs of this species. In this review, we present the advances in in vitro tissue culture and genetic transformation of C. odorata. The review includes our own experiences and data obtained in our laboratory. The low reproducibility and regeneration efficiency suggests the recalcitrance of C. odorata. We have established a protocol of somatic embryogenesis (SE) from shoots cultured on WPM medium with 2 mg/L of zeatin. Shoots were placed on different media with zeatin to generate embryogenic callus (80%). Histological analysis revealed the formation of undifferentiated cells, cell clusters with a high rate of mitosis, and the gradual formation of pro-embryonic masses and globular embryos. Transient genetic transformation through Agrobacterium tumefaciens achieved efficiencies of 6.25 to 8.5%. In addition, 250 mg/L of kanamycin was found to be the inhibitory dose to select T0. Despite this progress, it is necessary to optimize the process of somatic embryogenesis for C. odorata. An optimized protocol will allow the development of conservation strategies and synthetic seed technology, the commercial mass propagation, genetic improvement and production of secondary metabolites for C. odorata.