Maria L. Lopes

Somatic embryogenesis and plant regeneration in myrtle (Myrtaceae)

Somatic embryos of myrtle (Myrtus communis L.) were induced from mature zygotic embryos cultured in MS medium supplemented with several concentrations of 2,4-D (2.26 μM – 18.98 μM) or Picloram (2.07 μM – 16.5 μM) combined with 0.087 M or 0.23 M sucrose. For all the concentrations of 2,4-D or Picloram tested, 0.087 M sucrose proved to be more effective than 0.23 M. The best frequencies of induction were obtained in a medium containing 2.26 μM 2,4-D in which 97.3% of the explants produced somatic embryos. Although most embryos were produced from the adaxial side of the cotyledons, some of them differentiated from the hypocotyl. Secondary somatic embryos were often seen arising from the periphery of the former somatic embryos. Somatic embryo development was not synchronous but practically all the embryos germinated well after being transferred to media containing GA3 (0.29, 0.58 and 1.44 μM) alone. When benzyladenine was combined with gibberellic acid, germinating somatic embryos produced adventitious shoot buds which contributed to an increase in plantlet regeneration. Histological observations suggested that somatic embryos arise from the upper surface of the cotyledons probably from peripheral cells. Polyphenol-rich cells were usually seen in association with meristematic-like cells from which somatic embryos originate or with earlier steps of somatic embryo differentiation. Regenerated plants were phenotypically normal, showing a diploid (2n = 22) set of chromosomes.

EFFECT OF PLANT GROWTH REGULATORS AND GENOTYPE ON THE MICROPROPAGATION OF ADULT TREES OF ARBUTUS UNEDO L. (STRAWBERRY TREE)

Arbutus unedo grows spontaneously around the Mediterranean basin. The species is tolerant to drought and has a strong regeneration capacity following fires making it interesting for Mediterranean forestation programs. Considering the sparse information about the potential of this fruit tree to be propagated in vitro, a project to clone selected trees based on their fruit production was initiated a few years ago. The role of several factors on A. unedo propagation was evaluated. The results showed that 8.9 μm kinetin gave the best results although not significantly different from those obtained with benzyladenine or zeatin. The inclusion of thidiazuron or 1-naphthaleneacetic acid promoted callus growth and had deleterious effects on the multiplication rate. The genotype of the donor plants is also a factor interfering with the multiplication. The results also indicated that the conditions used for multiplication influenced the behavior of shoots during the rooting phase.

Somatic embryogenesis in myrtaceous plants

The Myrtaceae is a large family that includes about 3.000 species distributed by over 100 genera (Heywood, 1993; Paiva, 1997). Most species are concentrated in the South hemisphere, specially in tropical and subtropical regions of Australia, South and Central America and Southeast Asia (Heywood, 1993). A few species can be found in Southern Europe and North Africa, surrounding the Mediterranean sea. Eugenia and Eucalyptus are the genera including the highest number of species, whereas Myrtus communis is the only species native to Europe. Some species of Eucalyptus (e.g. E. citriodora, E. globulus) were introduced in several regions of Europe (Paiva, 1997). Meanwhile, they became the dominant species in some areas of Portugal and Spain (Mcvaugh, 1963).

Somatic Embryogenesis Induction in Tamarillo (Cyphomandra betacea)

Cyphomandra betacea (Cay.) Sendtn. usually known as tamarillo or tree tomato, is a solanaceous soft wood tree (Fig. 1A) grown for their edible fruits (Fig. 1B). The species, which may reach 2 – 4 meter height (Slack, 1976), produces tomato-like red, orange or yellow fruits according with the cultivars. The fruits of the red cultivar are the most popular due to their more striking appearance and better flavour (Slack, 1976). They are generally 2 – 3 inches long and 2 inches in diameter possessing many seeds (Hooker, 1899). Also included in the same genus are the species Casana (Cyphomandra casana), Mountain Tomato (C. crassifolia) and Guava Tamarillo (C. fragans). The plant can be propagated by seeds or cuttings (Fougue, 1973) or it may be grafted in Solanum mauritianum (Slack, 1976). In the first case, plants do not usually come true-to-type rendering difficult the propagation of selected genotypes (Barghchi, 1998). Several authors (see section 1.3) have also reported protocols for in vitro regeneration. The first pinkish flowers appear in spring, while the mature fruits are collected from October to April (Guimaraes et al., 1996). However, flower appearance and fruit maturity can be changed by pruning (Slack, 1976).

Somatic Embryogenesis Induction in Bay Laurel (Laurus nobilis L.)

Bay laurel or sweet bay (Laurus nohilis L.) is a member of the Lauraceae family, which includes about 2.500 species originating, predominantly, from tropical and subtropical regions with a few native to temperate climates (Heywood, 1993). Some of these species (e.g. Persea americana, Cinnamomum cantphora, Sassafras sp., Ocotea sp., Litsea sp.) are important sources of fruits, chemicals (oils) and timber. The genus Laurus comprises the species L. azorica which is confined to the Canary, Azores and Madeira islands, and L. nobilis which spread around the Mediterranean basin and is found in some areas of Portugal (Tutin, 1964). In Roman times, bay laurel was a symbol of glory and knowledge, being used to crown poets and heroes (Lanzara et al., 1978), a tradition kept for many centuries afterwards.