Regeneração in vitro e morfogênese de embriões somáticos em mandioca

In this study, the somatic embryogenesis and regeneration of Cigana Preta plants from shoot apices and immature leaves taken from plants cultivated in vitro were examined. To embryo induction the explants were cultivated in Murashige and Skoog (MS) medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) or 4-amino-3,5,6-trichloropicolinic acid (Picloram) at concentrations of 8.0 and 12 mg L-1. To development of embryos two media cultures with different concentration of BAP (D1 or D2) were evaluated. Embryos in the cotyledonary stage were incubated in germination medium containing MS salts and vitamins, 2.0 mu M copper sulfate, 2.4 g L-1 of Phytagel (R) and 1.77 mu M BAP. The highest frequency of calluses and the greatest number of embryos per explant were obtained using the auxin picloram at a concentration of 8.0 mg L-1. The plants regenerated in the picloram treatment exhibited normal development and were transferred to a multiplication medium after a minimum of four weeks. The histological sections of the malformed embryos from foliar explants cultured in the presence of 2,4-D demonstrated that the origin of the cotyledonary structures was independent of the formation of the shoot apical meristem, which was not formed in the embryos, and the majority of the embryos were classified as cornet-shaped. This study demonstrates that in cassava, the use of different auxins provides different conditions for the formation of somatic embryos, and the low rate of conversion into plants results from abnormalities in the embryos.