The present study confirms the occurrence of secondary somatic embryos in peach palm and describes a feasible protocol for regeneration of peach palm in vitro. Further optimizations include the use of explants obtained from adult palms and improvement of somatic embryo conversion rates.

The factors affecting the induction and development of somatic embryos and plantlet acclimatization of peach palm (Bactris gasipaes Kunth) were evaluated to establish an efficient regenerative protocol based on somatic embryogenesis. Mature zygotic embryos were cultured in Murashige and Skoog (MS) medium supplemented with 0-40 μM of picloram (4-amino-3,5,6-trichloropicolinic acid) and 0 or 5 μM of 2-isopentyladenine (6-dimethylaminopurine) (2-iP). After 5 mo. in culture embryogenic callus arose from primary calli. Picloram (10 μM) was effective in inducing embryogenic calli in 9.8% of the explants. The use of 1 μM of AgNO 3 enhanced embryogenic competence. Embryogenic calli showed an organized structure, a globular aspect, and were white to yellowish in color. Histological analyses showed that cell proliferation arose from subepidermal cells adjacent to vascular bundles, resulting in primary callus formed by a meristematic zone from which somatic embryos arose. Protein profile analyses revealed two high molecular mass bands in these embryogenic calli, but not in other tissues. Embryogenic calli were transferred to a culture medium containing 40 μM of 2,4-dichlorophenoxyacetic acid, 10 μM of 2-iP, plus 1 g l −1 of glutamine, hydrolyzed 0.5 g l −1 casein, and activated 1.5 g l −1 of charcoal. Morphogenetic responses achieved in this medium were the development of somatic embryos, rooting, and loss of embryogenic capacity. Somatic embryos were converted to plantlets on MS medium plus 24.6 μM of 2-iP and 0.44 μM of naphthalene acetic acid. Plantlets were maintained in MS medium with activated charcoal (1.5 g l −1 ) until they were 6 cm tall, and then acclimatized. After 16 wk, 84.2±6.4% survival was observed.

The present study suggests that the TCL somatic embryogenesis protocol developed is feasible, although it still requires further optimization for in vitro multiplication of peach palm, especially the use of similar explants obtained from adult palm trees.

5-Azacytidine combined with 2,4-D increases the number of Acca sellowiana somatic embryos. Global DNA methylation is directly affected by these compounds.

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Various factors affect the induction of somatic embryogenesis in peach palm (Bactris gasipaes Kunth). Among these, both the type and level of auxins had the greatest influence on in vitro responses, although the genotype and the developmental stage of the explants also influenced results. Younger inflorescences were more competent to respond to SE induction than more mature inflorescences and the use of a pre-treatment with 2,4-D (200 lM) in liquid MS culture medium also increased the embryogenic capacity, and diminished the development of flower buds. Higher oxidation rates were observed in explants maintained on 2,4-D-supplemented culture medium, while on 300 lM or 600 lM Picloram and Dicamba lower oxidation rates were observed. The progression from floral meristem to flower bud occurred at high frequency when low concentrations of auxins were used, independent of the type. Higher concentrations of Picloram or Dicamba reduced or even inhibited flower bud development. Picloram also enhanced the embryogenic induction rate more than 2,4-D and Dicamba, and among the concentrations evaluated 300 lM Picloram enhanced induction for both genotypes, with significant differences between genotypes. The best combination of variables used the least mature inflorescence (Infl1) from genotype I with the 2,4-D pre-treatment and 300 lM Picloram to generate 5 embryogenic calli from 18 explants; 26 embryos were obtained on average from each embryogenic callus. From these, eighteen embryos converted to plantlets and six of these survived transfer to the greenhouse.

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