In the last century, the genus Eucalyptus became an important multipurpose source of timber in many industrial applications for the production of pulp and paper, charcoal, energy, furniture, and housing. The genus Eucalyptus is a member of the Myrtaceae family, mainly originated from Australia, comprising of more than 700 species (Brooker, 2000). The trees form tall open forests, woodlands, and occur in environments ranging from areas of high rainfall to semi-arid regions, and from sea level to subalpine altitudes. A few species have been described as occurring outside the Australian territory (Eldridge et al., 1994); Eucalyptus deglupta is endemic to the Indonesian islands of Sulawesi and Ceram, Mindanao in the southern Philippines, northern New Guinea, and New Britain; E. urophylla, E. orophila occur in Timor and adjoining islands of the Lesser Sunda group (Pryor et al., 1995). Several factors contributed to the success of Eucalypts; the fast growth rate and large biomass production, the ability to grow in a wide range of environments and soils, good wood quality for solid wood products and short cellulose ﬁber, suitable for pulp production, particularly for paper and tissue. A considerable number of Eucalyptus plantations were established in the early 1900s in Brazil and South Africa along the railway tracks providing charcoal for the locomotives. Today, several countries in Asia, South America, southern Europe, and Africa, have an estimated area of planted forest around 16–19 million hectares (FAO, 2000). The predominance species in commercial plantations (around 80%) are Eucalyptus grandis, Eucalyptus camaldulensis and their hybrids (Potts, 2004). E. grandis, E. urophylla and their hybrids are mainly planted in tropical and subtropical regions, while E. globulus is preferred in temperate climates (Potts, 2004). One important factor determining the expansion of large areas of commercial Eucalyptus plantations was the development of cloning techniques, initiated in 1975 in the Popular Republic of Congo (Delwaulle et al., 1983). Outstanding genotypes, usually hybrids, having large and straight trunk with good wood properties were selected to make rooted cuttings and planted in large extensions of land. Vegetative propagation has been intensively used by the pulp and paper industry, producing highly uniform timber and allowing further gains in productivity in the pulping process. In the mid 1970s the development of tissue culture techniques and in vitro propagation of Eucalyptus spp. provided new opportunities for mass propagation, on a commercial scale, of selected genotypes.
At the same time, the growing importance of Eucalyptus for the pulp and paper industry, particularly in South America and Africa, led to the establishment of breeding programs selecting better hybrids for cloning and to improve the basic populations introduced from Australia. In the last 10 years, the advances in tissue culture techniques, plant regeneration, and genetic transformation, using mainly the Agrobacterium system, allowed the development of the ﬁrst transgenic Eucalyptus trees. Also, advances in the use of molecular markers have played an important role in helping breeders to select Eucalyptus trees with better wood quality, disease resistance, and stress tolerance. More recently, the development of genomic approaches, such as major expressed sequence tag (EST) sequencing programs, have increased the interest in the application of biotechnological tools in order to produce better Eucalyptus trees.