CBN-V Video Archives - S7-24
Genetic Transformation of Friable Embryogenic Callus in Cassava: Different Strategies, Problems and Prospects

Raemakers C.J.J.M, M.M. Schreuder, I. Pereira, E..Jacobsen and R.G.F. Visser

The Graduate School of Experimental Plant Sciences, laboratory of Plant Breeding, Wageningen University, P.O.B. 386, 6700 AJ Wageningen Krit.Raemakers@PV.DPW.WAU.NL

        In principle a successful genetic modification method is composed of 3 elements: gene transfer, selection for transgenic tissues and plant regeneration. All regeneration methods employed for genetic modification in cassava use somatic embryogenesis. One method makes use of a direct system of somatic embryogenesis, another an indirect form of somatic embryogenesis and in the third somatic embryos are cultured for adventitious shoot formation. The indirect form of somatic embryogenesis, described in literature as friable embryogenic callus (FEC), is the most commonly used method at this time. FEC is initiated at low frequencies from direct embryogenic tissues when these are switched from a Murashige and Skoog based mediumn to one consisting of Greshoff and Doy basal salts. FEC has been genetically modified using particle bombardment, Agrobacterium and electroporation of protoplasts. Selection of genetically modified plants has been accomplished using the luc, pat, hgp, and nptII genes and cassava has been successfully modified with the anti-sense agp-ase, gbss, and dad genes. Agronomic improvement of a specific cassava genotype via genetic modification is only possible if that genotype is amenable for FEC induction, gene transfer, regeneration and yields high quality plants. In our laboratory only 3 of the 10 tested genotypes met these criteria. This suggests that the current protocols for genetic modification should be combined with classical breeding techniques, or the current protocols should be optimized further and that and alternative protocols should be developed.

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