Cedrela odorata L. is a valuable tropical tree widely appreciated for its wood. This species confronts serious problems due to both overexploitation of its natural populations and its susceptibility to the Meliaceae borer Hypsipyla grandella, which destroys the apical meristems and produces structural deformations. The rapid introduction of new varieties through clonal forestry has been demonstrated to be the most effective way to improve the production of perennial plantation species. In this work, we report both a protocol for the rejuvenation of elite mature trees of C. odorata and the optimization of an in vitro culture system to scale up micropropagation. Several media formulations and the use of temporary immersion culture in bioreactors were evaluated. The addition of 20% coconut water to TY17 medium increased the number of adventitious shoots from hypocotyl segments to an average number of 4.68 shoots per explant. To replace coconut water and to define the culture medium, several cytokinins were tested at various concentrations; however, none of them produced the effect of coconut water. Rejuvenation of elite mature individuals was investigated by ex vitro grafting of mature tree twigs onto 3-mo-old juvenile trees.Although the grafting had a positive effect on the micropropagation of mature material, the multiplication rate of 1.5 new shoots per explant did not compare to the organogenic capacity of younger materials. Shoot and root elongation as well as acclimatization to ex vitro conditions were carried out in a temporary immersion culture of juvenile material using BioMINT® bioreactors. A 3.5-fold increase in shoot elongation and a 4-fold increase in root elongation were achieved compared to material cultured on semisolid media. Furthermore, this culture system allowed for 98% effectiveness in the soil adaptation of the in vitrogrown plants. The scaled-up multiplication capacity over a period of 6 mo calculated for the system is above 16,000 plants per mother plant with young materials but is only 125 with mature materials.

Tabebuia donnell-smithii is a tropical tree species that is highly important as a forest crop due to both environmental and economic benefits. Wood from these trees is in high demand, achieving up to three times the price of wood from Pinus species. Commercial plantations of this species help to reduce the pressure on natural populations; however, plantations are few in number due to the lack of domesticated varieties and the relative unavailability of seeds. Therefore, there is an urgent need for a reliable source of plantlets suitable for commercial production. In the present work, we report the clonal propagation of T. donnell-smithii from twigs collected from elite trees. Emerging axillary shoots were used as a source of explants. Fungal contamination was a persistent problem but was partially overcome by brief exposure to low concentrations of chlorine. The stem fragments that were used as an explant source were cultured in woody plant medium containing 30 μM zeatin. This was the best condition for inducing adventitious shoot proliferation, producing 2.8 shoots per explant. Coconut water had an additional positive effect, increasing the number of shoots per explant by a factor of up to 3.6. The shoots were rooted in medium containing 20 μM indole-3-butyric acid. Ninety-four percent of the rooted plants survived the transfer to soil.

Spanish red cedar (Cedrela odorata L.) is a tropical timber tree native to the Americas from southern Mexico to northern Argentina. Commercial plantations are scarce and, consequently, natural populations are overexploited. Traditional propagation practices for the establishment of large-scale plantations have had limited success in this species due to the relative scarcity of seeds, its broad genetic diversity and the lack of domesticated varieties. In vitro clonal propagation provides an effective method to overcome this situation and increase the yield of commercial plantations through the rapid multiplication of elite materials. Somatic embryogenesis (SE) is one of the most promising strategies for tree propagation due to the possibility of producing artificial seeds, the ability to store and rapidly mobilize germplasm and the opportunity for genetic manipulation. We report here the induction of indirect SE in C. odorata from calli derived from immature zygotic embryos after 12 weeks of culture. Macroscopic, histological, and scanning electron microscopic analyses of the calli revealed the presence of embryogenic cell clusters that formed cotyledonary embryos with clear bipolar structures and no vascular connections with the mother tissue. Different media preparations containing combinations of diverse auxins and cytokinins are known to have different effects on the type and frequency of embryogenic structures. Embryo conversion was achieved using an MS-based medium [Murashige T, Skoog F (1962) Physiol Plant 15:473-497, 1962 supplemented with abscisic acid, and transfer to soil was successful at a rate of 75%. The method described here provides a basis for optimizing the clonal propagation and genetic manipulation of this valuable species.

The choice of a method to culture red cedar tissues depends on the final objectives pursued. If homogeneous clonal material is required for experimental purposes, the easiest way is to generate the lines through adventitious shoot induction from seedlings germinated from seeds. If the objective is to generate high yielding material for plantation purposes, the choice will be the same method but starting from mature vegetative tissues from selected elite plants. Most of the process are the same, but the initial steps are less efficient and much more elaborate. If the purpose is to generate lines with new genetic characteristics through somaclonal variation, mutagenesis, or genetic transformation, somatic embryogenesis will be required. No single method in its present form is suitable for all purposes. Eventually, the efficient production of somatic embryos from rejuvenated shoots collected from mature selected plants is the ideal way to culture this species, but for the time being we have to choose one or the other. In this chapter, we present a grafting procedure to rejuvenate and maintain mother plants in the greenhouse and the in vitro culture systems we have developed for the production of Cedrela odorata propagules using explants from both young seedlings and mature tissues from selected old trees. Using a modified TY17 medium and the BioMINT(®) temporary immersion system, we obtained high multiplication and ex vitro transplantation rates for efficient large-scale propagation of this species.