Bibliography

Cassava is one of the most important sources of carbohydrates for over 500 million people in the (sub)tropics. Cassava plays an important role in the food security of many developing nations, especially in sub-Saharan Africa (SSA). Cassava is highly heterozygous, genetically complex, and many varieties either do not flower or produce few seeds thus hampering conventional crop improvement. Several major constraints limit the production and utilization of cassava roots, including two viral diseases, the Cassava Brown Streak Disease (CBSD) and the Cassava Mosaic Disease (CMD), which are specific to SSA. Farmer-preferred landraces are often susceptible to CBSD and/or CMD. Genetic transformation of cassava could complement conventional breeding programs for CBSD and/or CMD resistance. Current protocols for genetic transformation of cassava are limited to model genotypes which are not used by farmers of breeders in SSA. Since transformation protocols are genotype-dependent, suitable procedures for genetic modification of the landraces need to be developed. We have established somatic embryogenesis and organogenesis for three farmer/breeder-preferred varieties, two from East Africa (cv Kibaha and cv Albert) and one from West Africa (TME12) which are susceptible to CBSD. Primary and cyclical somatic embryogenesis was established for the three varieties. Cotyledon tissues from somatic embryos were used as source explants for Agrobacterium-mediated genetic transformation. Using an intron-interrupted â�glucuronidase reporter gene construct under control of the Cassava vein mosaic virus promoter, stably transformed cassava tissues and plants were obtained. Molecular evidence for stable expression of the transgenes will be presented.