| Environmental stability of resistance to anthracnose and virus diseases of water yam (Dioscorea alata), Egesi, C. N.*, Onyeka, T. J.* and Asiedu, R., in: African Journal of Agricultural Research, volume 4, number 2, pages 113-118, ISSN 1991-637X, 2009. |
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| Keywords: | Colletotrichum gloeosporioides; genotype x environment (G x E) interaction; stable resistance; water yam; yam anthracnose; yam mosaic virus
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| Cassava improvement in sub-Saharan Africa: contributions of IITA and its partners, Dixon, A., Okechukwu, R., Ssemakula, G., Hanna, R., Thresh, J. M., Hughes, J., Ingelbrecht, I., Fregene, M.*, Legg, J., Mahungu, N., Nweke, F., Ntawuruhunga, P., Fauquet, C., Manyong, V., Neuenschwander, P., Whyte, J., Wydra, K., Asiedu, R., Egesi, C. N.*, Bandyopadhyay, R., Winter, S., Tarawali, G., Bokanga, M., Ezedinma, C., Sanni, L., Ferguson, M., Ogbe, F., Akoroda, M., Maziya-Dixon, B., Ilona, P., Ekanayake, I. J., Ariyo, O., Onyeka, J.*, Otim-Nape, G.*, Dahniya, M. T., Ortiz, R., Hahn, S. K. and Hartmann, P., 2008. |
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Abstract:
Cassava improvement in sub-Saharan Africa: contributions of IITA and its partners
Dixon, A.G.O., R.U. Okechukwu, G. Ssemakula, R. Hanna, J.M. Thresh, J.d'A. Hughes, I. Ingelbrecht, M. Fregene, J. Legg, N. Mahungu, F. Nweke, J.P. Legg, P. Ntawuruhunga, C. Fauquet, V. Manyong, P. Neuenschwander, J. Whyte, K. Wydra, R. Asiedu, C.N. Egesi, R. Bandyopadhyay, S. Winter, G. Tarawali, M. Bokanga, C. Ezedinma, L. Sanni, M. Ferguson, F.O. Ogbe, M. Akoroda, B. Maziya-Dixon, P. Ilona, I.J. Ekanayake, O. Ariyo, J. Onyeka, G.W. Otim-Nape, M.T. Dahniya, R. Ortiz, S.K. Hahn and P. Hartmann
Cassava is well recognized for its capacity to address food needs of vulnerable communities in unstable environments in SSA. IITA and colleagues in African NARS, in collaboration with CIAT and ARIs have played leading roles in the development of improved cassava varieties which are disease and pest resistant, early maturing, and high yielding. Through a combination of conventional and new approaches, over 400 cassava genotypes have been developed. The characteristics of the new generation of cassava germplasm broke what had been an apparent yield barrier in cassava improvement increasing yields in many locations by at least 50-100% without the use of fertilizer. The improved germplasm is shared with NARS within the region as specific genotypes or improved seed populations for evaluation and selection under local conditions. Improvement programs in Africa that received these materials have tested them under local conditions, selected varieties that outperform local varieties, and released them to farmers in virtually every major cassava producing country. Today, about 30% of the area cropped with cassava in Africa is planted with improved varieties. Without the introduction of more productive cultivars with multiple diseases and pest resistance, the effective biological control of the cassava mealybug and, to a certain extent, of the green mite, cassava production in SSA would be 50% or less of what it is today. That translates to over 13 million tons of dry cassava/year, enough to meet the calorie requirements of 65 million people. The significant gains in the crop's output in farmers' fields are not only contributing to the African diet but also propelling commercialization of the crop. This paper highlights contributions to cassava improvement in SSA since 1970 by IITA and its partners, and suggests areas needing strengthening in the drive to produce better crop varieties for different regions and enduses in Africa.
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| Somatic embryogenesis and genetic transformation of African farmer-grown cassava genotypes that are susceptible to the Cassava Brown Streak Disease, Ingelbrecht, I., Raji, A., Oyelakin, O., Winter, S., Moller, B., Dixon, A. and Jorgensen, K., 2008. |
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Abstract:
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 {\^a}{\"i}¿½glucuronidase 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.
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