The International Development Research Centre is a public corporation created by the Parliament of Canada in 1970 to support research designed to adapt science and technology to the needs of developing countries. The Centre's activity is con­ centrated in five sectors: agriculture, food and nutrition sciences; health sciences; information sciences; social sciences; and com­ munications. IDRC is financed solely by the Parliament of Canada; its policies, however, are set by an international Board of Governors. The Centre's headquarters are in Ottawa, Canada. Regional offices are located in Africa, Asia, Latin America, and the Middle East. © International Development Research Centre 1982 Postal Address: Box 8500, Ottawa, Canada KlG 3H9 Head Office: 60 Queen Street, Ottawa, Canada International Institute of Tropical Agriculture, Ibadan NG International Development Research Centre, Ottawa CA IDRC-177e Root crops in Eastern Africa : proceedings of a workshop held in Kigali, Rwanda, 23-27 Nov. 1980. Ottawa, Ont., IDRC, 1982. 128 p. : ill. /Root crops/, /plant breeding/, /genetic improvement/, /agricultural research/, /East Africa/-/plant protection/, /plant diseases/, /pests of plants/, /cassava/, /sweet potatoes/, /conference report/, nist of participants/. UDC: 633.4(67) ISBN: 0-88936-305-6 Microfiche edition available IDRC-177e Root Crops in Eastern Africa Proceedings of a workshop held in Kigali, Rwanda, 23-27 November 1980 Cosponsored by Gouvernement de la Republique rwandaise, the International Institute of Tropical Agriculture, and the International Development Research Centre. Resume Cette brochure traite principalement des deux tubercules alimentaires les plus importants en Afrique orientale, soit le manioc et la patate douce. Quelques communications. portent sur la pomme de terre, l'igname, le taro et l'" enset » dont la consommation est considerable dans plusieurs pays de la region. Le rendement de ces cultures est limite par de nombreux facteurs. Aussi, la recherche effectuee dans le c~dre de programmes agronomiques nationaux et internationaux est-elle orientee vers la correction de cette situation en Afrique. Les difficultes rencontrees en cours de travaux et les progres realises sont decrits par des representants et des consultants de l'Institut international d'agriculture tropicale d'Ibadan (Nigeria) et d'autres pays tel que le Cameroun, le Kenya, l'Ouganda, le Malawi, le Zimbabwe, l'Ethiopie, le Burundi, le Zai:re et le Swaziland. Resumen Esta publicaci6n se enfoca en la mandioca y el camote - los cultivos de tuberosas mas importantes del Africa oriental. Los trabajos tratan tambien del Solanum tuberosum, Dioscorea spp., Colocasia sp., Xanthosoma sp., y Enset sp., que son todos cultivos importantes a los paises de esta region. La producci6n de cada uno es restringida por serios constrefiimientos, y el alivio de estos es el objetivo de varias investigaciones llevadas a cabo por los programas agrl'.colas nacionales e in­ ternacionales en el Africa. El progreso hacia y los problemas encontrados en llegar a este fin son delineados por especialistas representando al Instituto Internacional de Agricultura Tropical en Ibadan, Nigeria, y a los paises de Camerun, Kenia, Uganda, Malawi, Zimbabwe, Etiopia, Burundi, Zaire, y Swazilandia. Contents Foreword 5 Participants 7 Discussion summary 10 Breeding Historical perspectives of cassava breeding in Africa B.D.A. Beck 13 Research priorities, techniques, and accomplishments in cassava breeding at IITA S.K. Hahn 19 Research priorities, techniques, and accomplishments in sweet-potato breeding at UTA S.K. Hahn 23 Sweet-potato improvement in Rwanda M.J.J. Janssens 27 Sweet-potato improvement in Cameroon H.J. Pfeiffer 33 Strategy for developing a national potato program for Rwanda P. Vander Zaag 39 Plant protection Increasing and stabilizing cassava and sweet-potato productivity by dis­ ease resistance and crop hygiene E.R. Terry and S.K. Hahn 47 Effects of soil fertility on cassava bacterial blight in Rwanda I. Butare and F. Banyangabose 53 Distribution and importance of Xanthomonas manihotis and X. cassavae in East Africa D.M. Onyango and D.M. Mukunya 56 Cassava mosaic disease E.J. Guthrie 59 Pest control for cassava and sweet potato K. Leuschner 60 Cassava green mite: its distribution and possible control Z.M. Nyiira 65 Biological control of cassava mealybug and cassava green mite: front-line release strategy K.M. Lema and H.R. Herren 68 The mealybug problem and its control T.P. Singh 70 Agronomy Economics of research and development of root and tuber crops in Zanzi­ bar, Tanzania A.J. Carpenter 75 Agronomic research on cassava cultivation in Rwanda J. Mulindangabo 78 Agronomic effects and economic importance of fertilizers on yams m Cameroon S.N. Lyonga 81 3 4 ROOTCROPS Country reports Cameroon H.J. Pfeiffer and S.N. Lyonga 89 Kenya G.H. de Bruijn and E.J. Guthrie 95 Uganda Z.M. Nyiira 99 Malawi R.F. Nembozanga Sauti 104 Zimbabwe A.G. Rowe 107 Ethiopia Terefe Belehu 109 Burundi D. Cimpaye 111 Zaire T.P. Singh and N.B. Lutaladio 114 Swaziland W. Godfrey-Sam-Aggrey 119 References 122 Foreword The Eastern Africa root-crop workshop was concerned with cassava, sweet potato, yams, and cocoyams, with particular emphasis on the first two crops because of their relative importance in Eastern Africa. None of these crops is indigenous to the area. Cassava was probably introduced from Latin America to the lowland coastal region of Eastern Africa by sea during the 18th century and to the highland regions oflakes Edward, Kwu, Victoria, Tanganyika, Malawi, and Bangwudu through western Zaire at about the same time or a little earlier. The similarity in the use of the crop within coastal and highland regions and the presence of bacterial blight only in the highland region suggest that it was introduced into Eastern Africa from two directions. When and how sweet potato was introduced into Eastern Africa are uncertain. It may, however, have been grown in the region before the arrival of Europeans. Although white yam (Dioscorea rotundata) and yellow yam CD. cayenensis) were domesticated in West Africa, they must have been introduced into Eastern Africa comparatively recently. The Asian water yam (D. alata) is more widely grown in Eastern Africa than is the African yam. The old cocoyam (Colocasia spp.), which was domesticated in Asia, was probably introduced into Eastern Africa during the 16th century through Egypt. The new cocoyam (Xanthosoma spp.), which was domesticated in Central America, was probably in­ troduced much later. Cassava and sweet potato were quickly and widely adapted; they became important staple-food crops in the traditional farming systems in different agroecological areas. They have the ability to adapt to diverse environmental conditions and farming systems. They can produce high yields in adverse conditions, can be grown with limited inputs, and are drought tolerant, surviving even 2-4 months of dry weather. When con­ ditions are favourable, they can recover from damage caused by insect pests and diseases. Since their introduction, they have played a vital role in alleviating famine conditions in the region by providing a sustained food supply when other crops fail. The leaves of both crops are used as a vegetable and are a major source of protein, vitamins, and minerals; the storage roots are used by the population as the major source of carbo­ hydrate. One often forgets the merits of these crops when conditions are favourable and other crops flourish. However, as the recent drought in the region showed, these crops are like lifeblood and deserve special attention. Active research and development are now taking place to use root crops for energy in countries that do not produce fuel, projects already being under way in Brazil, Japan, and Australia. Countries in Eastern Africa will also consider these projects in the future. 5 6 ROOT CROPS However, at present, yields of the root crops in the region are far too low to meet the demand and do not reflect the potential. Researchers have demonstrated that yields can be increased substantially through improved cultural practices and improved varieties. The importance of these root crops is, slowly but steadily, being real­ ized by government officials in many countries in Eastern Africa, although the opportunities to exchange research findings and views among re­ searchers and policymakers are few. This Eastern Africa root-crop work­ shop was, therefore, held so that researchers and policymakers could: • Discuss and identify the constraints to root-crop production in the region; • Establish means to work together internationally and nationally toward a solution of the production constraints; and • Consider future development and research in root crops in the re­ gion. The need for stock-taking and exchange among researchers so that they can move forward toward common goals has been recognized and increasingly supported by funding agencies. The International Develop­ ment Research Centre (Canada) and the Ford Foundation (USA), there­ fore, agreed to provide funds for the Eastern Africa root-crop workshop, the proceedings of which constitute this publication. S.K. Hahn International Institute of Tropical Agriculture and Andrew D.R. Ker Agriculture, Food and Nutrition Sciences Division IDRC Participants B.D.A. Beck Brian Beck (Pvt) Ltd, Box 86, Zomba, Malawi Moshi Bititaweho Universite nationale du Rwanda (UNR), B.P. 117, Butare, Rwanda Innocent Butare Institut des sciences agronomiques du Rwanda CISAR), B.P. 138, Buture, Rwanda A.J. Carpenter Food and Agriculture Organization of the United Nations (FAO), P.O. Box 159, Zanzibar, Tanzania D. Cimpaye Institut des sciences agronomiques du Burundi (ISABU), B.P. 795, Bujumbura, Burundi G.H. de Bruijn Department of Crop Science, University of Nairobi, P.O. Box 30197, Nairobi, Kenya Gilbert Delepierre Programme belge de recherches agronomiques au Rwanda (PBRA), B.P. 1051, Kigali, Rwanda A. Eid Food and Agriculture Organization of the United Nations (FAO), B.P. 445, Kigali, Rwanda Thaddee Gatarasi Institut des sciences agronomiques du Rwanda CISAR), B.P.