Progress made in FEC transformation of cassava

In cassava friable embryogenic callus (FEC) has been used to obtain transge nic plants using particle bombardment, electroporation, and Agrobacterium t umefaciens. FEC cultures have been obtained in 6 of the 10 tested genotypes . In all genotypes FEC could be regenerated into plants, however the effici ency differed between the genotypes. Almost all plants regenerated from 6 m onths old FEC cultures of TMS604444, Adira 4, Thai 5 and M7 were morphologi cal similar to control plants. However, in R60 and R90 a large number of pl ants were not identical to control plants. Older FEC lines of TMS60444 have a reduced ability to regenerate plants and the plants show somaclonal vari ation. Somaclonal variation is observed in the same extend in transgenic an d non-transgenic plants. The origin of this variation is both genetic and e pigenetic. Luciferase based selection is less efficient in producing transg enic lines than chemical selection. Furthermore Agrobacterium tumefaciens m ediated transformation is much more efficient than particle bombardment wit h respect to the production of transgenic lines. A tentative model is intro duced which best describes the effect of different selection regimes on the time period required to produce transgenic plants. Kanamycin and stringent luciferase selection required a shorter period of time than selection base d on hygromycin, phosphinothricin or non-stringent luciferase. However, a m ore significant reduction of time was obtained if young instead of old FEC lines of genotype TMS60444 were used for genetic modification. In accordanc e to the model these young FEC lines of TMS60444 produced transgenic plants within 4 months with both Agrobacterium tumefaciens combined with kanamyci n selection and particle bombardment combined with stringent luciferase sel ection.