Highland yellow single cross hybrid maize ears Credit, CIMMYT.

Highland yellow single cross hybrid maize ears
Credit, CIMMYT.

Some of the best advances in conventional plant breeding have been in the production of hybrid maize and rice. A cross-pollinating crop, maize seed is naturally a hybrid. Saved hybrid seed is usually highly variable and produces uncertain and often less favourable outcomes.  Significant improvements in maize seed breeding were not achieved until the discovery of ‘detasseling,’ by which the male flowers and their pollen are removed, preventing the plants from fertilising themselves. This paved the way for producing controlled crosses or hybrids that combined the best features of the breeding lines.[1] The process of hybridisation is now more sophisticated and costly to produce hybrid varieties for specific environments. Today, farmers have a choice between open-pollinated varieties (OPVs) (pollination that occurs without deliberate cross-breeding of two separate parent lines) and hybrid varieties, each with advantages and disadvantages. OPVs produced by farmers are usually genetically diverse and not very uniform, but over time the plants become well adapted to their environments. Their costs may be low, but they tend to yield 10% to 25% less than hybrids.[2] In comparison, hybrids are very uniform, but their seeds need to be repurchased each year because their vigour (desired characteristics such as yield, rate of growth and maturity) diminishes with each generation.[3]  
Hybrid rice. Credit, IRRI.

Hybrid rice. Credit, IRRI.

Hybridisation of rice is more complicated because it is a self-pollinated crop and the male and female organs grow on the same floret and only flower for a short time. When the male and female organs do not occur in separate flowers, producing hybrids can be tedious and expensive as a series of delicate, exacting and properly timed operations that must be done by hand are often required. Recently, a built-in cellular system of pollination control known as cytoplasmic male sterility (CMS) has made hybrid varieties of rice and a wide range of other self-pollinating plants, fruits and vegetables possible.[4] Despite advances in hybrid seed technologies, seed systems and breeding programs in Africa remain underdeveloped, underfunded and fragmented, especially when it comes to reaching and meeting the needs of smallholder farmers. From 1966 to 1990, African public maize breeding programs released close to 300 varieties, of which 100 were hybrids.[5] The yield gains were estimated to be 30% in dry areas and 40% in favourable environments, but wide-scale adoption remains low in most countries, with a few notable exceptions: Kenya, Zambia, and Malawi.[6] Generally, the formal sector only accounts for a small portion of the seed used by farmers in Africa; most seed is produced by, saved by and exchanged with other farmers. More than 80% of the seed planted in sub-Saharan Africa originates from informal systems.[7] Contribution to Sustainable Intensification
The development of hybrid maize seed has had one of the greatest impacts on increasing the quantity of available food supply.[8] Hybrid rice – grown on more than 21 million hectares, or 13% of land devoted to rice globally – too has contributed substantially to global food production. Hybrid rice increases yields between 5% and 15% over inbred varieties and China’s “super” rice achieves yields of 12 tonnes per hectare or 8% to 15% more than other hybrid varieties.[9] Hybrid seeds are usually an improvement over non-hybrids in terms of qualities such as yield, resistance to pests and diseases, and time to maturity.[10] In addition to qualities like good vigour, trueness to type, heavy yields and high uniformity, other characteristics such as earliness, disease and insect resistance and good water holding ability have been incorporated into most hybrids varieties. Hybridisation can also be very useful in developing seed varieties that are drought and pest tolerant, enabling adaptation to climate change or mitigating other risks. As these cultivars have higher yield potential, under the right inclusive markets and climatic conditions, they can contribute to the improvement of farmers’ income and asset accumulation as well as the improvement of their standard of living.[11]
Benefits and limitations
Yield Benefits
The advantage of growing hybrid seed compared to inbred, open-pollinated lines comes from the ability to cross the genetic materials of two different, but related plants to produce new, desirable traits that cannot be produced through inbreeding or selection. Hybridisation can also be very useful in developing seed varieties that are drought and pest tolerant, enabling adaptation to climate change or mitigating other yield penalising risks. Hybrid seed also produces plants that are uniform, and usually higher in yield. Yield benefits vary by crop and environment, but some notable examples include maize hybrids developed by the International Institute for Tropical Agriculture (IITA) in West and Central Africa in the 1980’s that by the early 1990’s were available with resistance to maize streak virus and out-performed open-pollinated varieties (OPVs) by 33% to 45%.[12]
Costs to Smallholder Farmers
The main disadvantage of hybrid seed, especially for smallholder or resource-poor farmers, is that they do not perform to the same standards when their seed is saved for future plantings. Hybrid seed typically produces high yields the first year, but the yield drops if the seed is recycled for a second year. The percentage yield loss that occurs in recycling depends on the type of hybrid and the growing environment.[13] As a result, if farmers wish to achieve the same yields and or characteristics from season to season, they must continually repurchase the same seed. For farmers in developing countries, this can often be expensive or challenging if seed markets and credit are unreliable or inaccessible.
Sustainable Seed Systems
A sustainable seed system will ensure that high quality seeds of a wide range of varieties and crops are produced and fully available in time, acceptable and affordable to farmers. However, farmers are not always able to fully benefit from the advantages of using improved seed.[14] Part of these challenges will not be addressed without the development and improved access to finance and markets, but reforms and improvements are also needed within research and breeding programmes. Seed systems are usually divided into formal and informal; the former consisting of the development of new varieties by trained plant breeders and multiplied according to set standards and the latter informal seed selection, multiplication and exchange by farmers. Whilst the formal sector offers opportunities to create uniform, quality and reliable seed that offer greater yield or other desired benefits, these seeds can sometimes be cost-prohibitive. Informal systems are low cost and adaptable to farmer preferences and needs, and the use of multiple seed varieties on a farm can improve resilience to certain to shocks and stresses, but is limited in its ability to develop or widely disseminate new varieties.[15] As both approaches offer options for strengthening resilience against a variety of risks and uncertainties, and private seed companies have not demonstrated strong interest in producing seeds that are grown in small volumes, in remote areas or marginal areas, both systems should be strengthened.
Constrained research and development capacity
Developing sustainable seed systems includes the improvement of agricultural research and development for new seed varieties. The issues and progress in plant breeding vary widely across crops and countries but generally, there is a lack of national capacity in plant breeding, due to a low number of trained breeders, and limited capacity to develop robust delivery and extension systems. Through support from international agricultural research centres and donors to national agricultural research organisations (NAROs), improved germplasm has been adapted to local conditions for a variety of African staple crops. Only recently have universities and private sector companies become more involved in varietal development. Collaboration between all these actors has led to the development of several varieties of major food crops, especially maize, sorghum and rice in sub-Saharan Africa. In 7 West African countries, for example, more than 131 crop varieties were released between 2002 and 2012.[16] Notable advancements in public-private partnerships for improving drought-tolerant maize varieties is the Water Efficient Maize for Africa (WEMA), a collaboration between the African Agricultural Technology Foundation (AATF), the International Maize and Wheat Improvement Center (CIMMYT) and Monsanto to provide germplasm and seed varieties royalty-free.
A preference for maize
Maize is the most important cereal crop in sub-Saharan Africa. Africa produces 6.5% of maize globally, but accounts for 30% of worldwide consumption. Eastern and Southern Africa consumes 85% of its production for food, whilst Africa as a whole consumes 95%, compared to other regions of the world that use maize primarily as animal feed.[17] Although many other crops continue to be culturally important, offer more nutrients or strategies for diversification and resilience, maize receives the majority of attention from agricultural research and breeding programmes.[18] Recently, however, there has been growing attention to breeding other cereals such as millet and sorghum. Plant breeding has large fixed costs and long (5-20 years) and uncertain payoffs. Typically, only a large company or a subsidised public entity can afford to assume these risks.[19] In addition, many types of seed are easy to reproduce. Though, some seeds are difficult to harvest or store such as many vegetable seeds, others do not maintain their yield advantage if saved, as is the case with hybrid maize. Many self-pollinating crops including wheat, rice, groundnuts, and potatoes maintain their genetic characteristics over many generations. This explains why farmers generally will purchase vegetable and hybrid maize seed, but often use saved seed for other crops.[20] In addition to the difficulty for a company to recover its breeding costs when farmers save and re-use seed, limited consumer demand for other types of seed varieties from the formal sector also constrains investments in neglected crops and environments.
Adoption
In a number of countries, the use of hybrid cultivars in sorghum and maize production has been increasing, for example in Nigeria, Kenya and Zambia.[21] Rates of adoption, however, vary by country, region and farm typology and size. In Kenya, hybrid seed is more widely adopted by commercial rather than small-scale farmers.[22] The use of hybrid technology is also considerably higher in the South African commercial farming sector than in the smallholder sector.[23] In contrast, hybrid cultivars dominate agricultural food production systems of small-scale farming sectors in Zambia and Zimbabwe.[24] One study[25] noted that hybrid technology is likely to be adopted more extensively by farmers that have large farms. Farmers who have access to farming support services also tend to swiftly adopt new technology. In Kenya, for example, farmers’ access to credit, input supply and extension services enhanced the adoption of their new hybrid maize.[26] Another study found that gender and literacy levels affect adoption of new seed technologies. Although women constitute the majority of the subsistence farming community, men are more likely to adopt hybrid sorghum. Farmers with some level of education adopt the hybrid cultivars more than those without years of schooling. However, in other studies this has not been found to be a strong predictor of use.[27]  Distance to roads, access to transport infrastructure and farm size are found to influence the scale of hybrid seed planted by smallholder maize growers most significantly.[28] Further, the majority of farmers with membership in cooperatives use hybrid sorghum. Therefore, access to agricultural organisations may also have an impact on the farmer adoption of technology. In Kenya, cost was cited as the strongest barrier to hybrid seed adoption.[29]
Plant breeder rights and farmer ownership of seeds
As genetic resources have assumed increasing scientific and (especially) commercial value, debates over access to and ownership of genetic resources have intensified. Seed is basic to crop production and thus food security and rural development.  The sustainable availability of good-quality seed is therefore an important development issue.[30] Trends emerging in the commercial seed industry which has become increasingly concentrated and now integrated into the pharmaceutical and chemical industries under the classification of ‘life-sciences’ companies generates concern among users. The concern is that corporate control over seed markets and genetic resources will disadvantage farmers no longer able to access, afford or save seed and lead to further consolidation of the farm sector in both developed and developing countries. Seeds have, therefore, also become an issue in debates on equity.[31]
Economic Impacts
The advantages of hybrids come at a price, because the performance of seeds diminishes in subsequent generations, requiring annual purchasing to maintain performance. Despite this reoccurring cost, the influence of hybrid seed on income and assets is favourable for smallholder maize growers in Kenya[32] and Zambia.[33] Although smallholders in Kenya, particularly in less favourable areas, have been reluctant to adopt hybrid maize varieties, well adapted varieties can be profitable in terms of yield and yield stability even in marginal areas under low input conditions.[34] Further, those that do not adopt the technology, can be considered disadvantaged.[35] In Zambia, the use of maize hybrids is associated with higher values of household income, assets, farm and processing equipment, livestock, and lower levels of deprivation compared to non-adopting farmers.[36] For every kilogram of hybrid maize seed planted, total household income increased by ZMK 32,230 (US$6,000) on average. Since this is considerably more than the price of hybrid seed in Lusaka ZMK 4,300 – 12,000 (US$0.59 – 1.65), hybrid maize proved profitable for Zambian smallholder farmers. If this profitability continues, returns will build productive assets and lessen the severity of poverty.[37]
References
  1. [1] Conway, G 2012, One Billion Hungry, Can We Feed The World? Cornell University Press, Ithaca and London.
  2. [2] Conway, G 2012, One Billion Hungry, Can We Feed The World? Cornell University Press, Ithaca and London.
  3. [3] Conway, G 2012, One Billion Hungry, Can We Feed The World? Cornell University Press, Ithaca and London.
  4. [4]  Eckardt, NA 2006, ‘Cytoplasmic Male Sterility and Fertility Restoration’ The Plant Cell, vol. 18, no. 3, pp. 515-517.
  5. [5] Maredia, MK, Byerlee, D & Pee, P 2000, ‘Impacts of food crop improvement research: evidence from sub-Saharan Africa’ Food Policy, vol. 25, pp. 531-559.
  6. [6] Mason, N & Smale, M 2014, ‘Hybrid Seed and the Economic Well-Being of Smallholder Maize Farmers in Zambia’ Journal of Development Studies, vol. 50, no. 5, pp. 680-695.
  7. [7] African Union 2008, African seed and biotechnology programme, African Union, Addis Ababa.
  8. [8] Encyclopedia Britannica (no date), Plant Breeding Available from: <http://www.britannica.com/science/plant-breeding/Hybrid-varieties> [2 July 2015].
  9. [9] GRiSP (Global Rice Science Partnership) 2013, Rice almanac, 4th edition International Rice Research Institute, Los Baños.
  10. [10] International Service for the Acquisition of Agri-Biotech Application (ISAAA) 2006, Conventional Plant Breeding, Pockets of Knowledge series, no. 13, International Service for the Acquisition of Agri-Biotech Application (ISAAA), Metro Manila.
  11. [11] Diale, NR 2011, ‘Socio-economic indicators influencing the adoption of hybrid Sorghum: The Sekhukhune District perspective’ South African Journal of Agricultural Extension, vol. 39, no. 1, pp.75-85.
  12. [12] Smith, J, Weber, G, Manyong, MV & Fakorede, MAB 1997, ‘Fostering sustainable increases in maize productivity in Nigeria’ In: eds. D Byerlee & CK Eicher, Africa's emerging maize revolution. Lynne Rienner, Boulder, pp. 107-124.
  13. [13] Minot, N, Smale, M, Eicher, C, Jayne, T, Kling, J, Horna, D & Myers R 2007, Seed development programs in sub-Saharan Africa: a review of experiences, Rockefeller Foundation, Nairobi.
  14. [14] Food and Agriculture Organisation of the United Nations (FAO) 2015, Seed Systems, Available from: <http://www.fao.org/agriculture/crops/core-themes/theme/seeds-gr/seed_sys/en/> [1 June 2015].
  15. [15] Minot, N, Smale, M, Eicher, C, Jayne, T, Kling, J, Horna, D & Myers R 2007, Seed development programs in sub-Saharan Africa: a review of experiences, Rockefeller Foundation, Nairobi.
  16. [16] Alliance for a Green Revolution in Africa (AGRA) 2013, Africa Agriculture Status Report: Focus on Staple Crops, AGRA, Nairobi.
  17. [17] International Institute of Tropical Agriculture (IITA) 2009, Maize, Available from <http://www.iita.org/maize> [12 June 2015].
  18. [18] Minot, N, Smale, M, Eicher, C, Jayne, T, Kling, J, Horna, D & Myers R 2007, Seed development programs in sub-Saharan Africa: a review of experiences, Rockefeller Foundation, Nairobi.
  19. [19] Minot, N, Smale, M, Eicher, C, Jayne, T, Kling, J, Horna, D & Myers R 2007, Seed development programs in sub-Saharan Africa: a review of experiences, Rockefeller Foundation, Nairobi.
  20. [20] Minot, N, Smale, M, Eicher, C, Jayne, T, Kling, J, Horna, D & Myers R 2007, Seed development programs in sub-Saharan Africa: a review of experiences, Rockefeller Foundation, Nairobi.
  21. [21] Smith, J, Weber, G, Manyong, MV & Fakodere, MAB 1997, ‘Fostering Sustainable Increases in Maize Productivity in Nigeria’ in: eds. D Byerlee & CK Eicher, Africa's Emerging Maize Revolution, Lynne Rienner Publishers, London pp.107-124.
  22. [22] (Morris, ML 1998, ‘Overview of the World Maize Economy’ in: ed. ML Morris, Maize Seed Industries in Developing Countries, Boulder: Lynne Rienner Publishers, NEPAD pp.13-34
  23. [23] Rusike, J & Eicher, CK 1997, ‘Institutional Innovations in the Maize Seed Industry’ in: eds. D Byerlee & CK Eicher, Africa's Emerging Maize Revolution, Lynne Rienner Publishers, London pp.173-192.
  24. [24] Rubey, L, Ward RW & Tschirley, D 1997, ‘Maize Research Priorities: The Role of Consumer Preferences’ in: eds. D Byerlee & CK Eicher, Africa's Emerging Maize Revolution, Lynne Rienner Publishers, London. pp.145-156..
  25. [25] Heisey, PW, Morris, ML, Byerlee, D & Lopez-Pereira, MA 1998, ‘Economics of Hybrid Maize Adoption’ in: ed. ML Morris, Maize Seed Industries in Developing Countries, Boulder: Lynne Rienner Publishers, pp.143-158.
  26. [26] Hassan, RH & Karanja, DD 1997, ‘Increasing Maize production in Kenya: Technology, Institutions, and Policy’ in: eds. D Byerlee & CK Eicher, Africa's Emerging Maize Revolution, Lynne Rienner Publishers, London pp.81-93.
  27. [27] Mason, N & Smale, M 2014, ‘Hybrid Seed and the Economic Well-Being of Smallholder Maize Farmers in Zambia’ Journal of Development Studies, vol. 50, no. 5, pp. 680-695.
  28. [28] Mason, N & Smale, M 2014, ‘Hybrid Seed and the Economic Well-Being of Smallholder Maize Farmers in Zambia’ Journal of Development Studies, vol. 50, no. 5, pp. 680-695.
  29. [29] Hassan, RH & Karanja, DD 1997, ‘Increasing Maize production in Kenya: Technology, Institutions, and Policy’ in: eds. D Byerlee & CK Eicher, Africa's Emerging Maize Revolution, Lynne Rienner Publishers, London pp.81-93.
  30. [30] Louwaars, N 2007, Seeds of Confusion: The impact of policies on seed systems. PhD Thesis, Wageningen University.
  31. [31] Louwaars, N 2007, Seeds of Confusion: The impact of policies on seed systems. PhD Thesis, Wageningen University.
  32. [32] Mason, N & Smale, M 2014, ‘Hybrid Seed and the Economic Well-Being of Smallholder Maize Farmers in Zambia’ Journal of Development Studies, vol. 50, no. 5, pp. 680-695.
  33. [33] Mathenge, MK, Smale, M & Olwande, J 2014, ‘The impacts of hybrid maize seed on the welfare of farming households in KenyaFood Policy, vol. 44, pp. 262-271.
  34. [34] Schroeder, C, Onyango K’Oloo, T, Nar Bahadur, R, Jick, NA, Parzies, HK & Gemenet, DC 2013, ‘Potentials of  Hybrid Maize Varieties for Small-Holder Farmers in Kenya: a review based on SWOT analysis’ African Journal of Food, Agriculture, Nutrition and Development, vol. 13, no. 2, Available from: < http://www.ajfand.net/Volume13/No2/Heiko11360.pdf > [1 July 2015].
  35. [35] Mathenge, MK, Smale, M & Olwande, J 2014, ‘The impacts of hybrid maize seed on the welfare of farming households in KenyaFood Policy, vol. 44, pp. 262-271.
  36. [36] Mason, N & Smale, M 2014, ‘Hybrid Seed and the Economic Well-Being of Smallholder Maize Farmers in ZambiaJournal of Development Studies, vol. 50, no. 5, pp. 680-695.
  37. [37] Mathenge, MK, Smale, M & Olwande, J 2014, ‘The impacts of hybrid maize seed on the welfare of farming households in KenyaFood Policy, vol. 44, pp. 262-271.

Case Studies

Download These Case Studies (pdf)
Case study 1: Makonnen Farm Ltd. Selling Hybrid Maize in Ethiopia
Maize. Credit USAID

Maize. Credit USAID

Alemayehu Makonnen is a local seed entrepreneur in the Southern Nations, Nationalities, and Peoples’ Region (SNNPR) in southwest Ethiopia who specialises in producing hybrid seeds with support from the Alliance for a Green Revolution in Africa (AGRA) Programme for African Seed Systems (PASS).[1]  Compared to other countries where AGRA operates, uptake of hybrid maize has been slow in Ethiopia, with fewer than 10% of farmers adopting the technology. This low level of adoption is likely due to the lack of availability of the seed through established seed systems.[2]

Makonnen cites the major reason why people do not use quality seeds and input as a lack of access. In 2011, he was able to expand his production of hybrid seed with the support of a US$200,000 grant from AGRA. He also started working with a Zimbabwean maize breeding company – Seed Co. Ltd. – to acquire the supply of the parent material for hybrid seed production.[3]

Following the expansion of Makonnen Farm Ltd., he was able to sell seed to 1,000 farmers. When other farmers saw the success of their crop, they became interested in buying the seed, resulting in sales to 6,000 farmers in 2012. By 2013, Makonnen was selling seed to 16,000 farmers and cultivating 100ha of land for the production of hybrid maize seed. He expects 20,000 customers in 2015, showing that adoption is growing. Makonnen reports that 80% of smallholders who buy his seed and use reasonably good management practices realise an average of 4t/ha, whilst some farmers have reached up to 6t/ha. This is in comparison to the national average of 2t/ha.[4]

References
  1. [1] Alliance for a Green Revolution in Africa, (AGRA) (no date), Adopting hybrid seed and changing fortunes in Ethiopia, Available from: <http://www.agra.org/agra/en/what-we-do/adopting-hybrid-seed-and-changing-fortunes-in-ethiopia/> [1 July 2015].
  2. [2] Alemu, D & Tripp, R 2010, Seed system Potential in Ethiopia: Constraints and opportunities for enhancing the system, International Food Policy Research Institute (IFPRI), Washington, DC.
  3. [3] Alliance for a Green Revolution in Africa, (AGRA) (no date), Adopting hybrid seed and changing fortunes in Ethiopia, Available from: <http://www.agra.org/agra/en/what-we-do/adopting-hybrid-seed-and-changing-fortunes-in-ethiopia/> [1 July 2015].
  4. [4] Alliance for a Green Revolution in Africa, (AGRA) (no date), Adopting hybrid seed and changing fortunes in Ethiopia, Available from: http://www.agra.org/agra/en/what-we-do/adopting-hybrid-seed-and-changing-fortunes-in-ethiopia [1 July 2015].
Case study 2: Hybrid sorghum builds resistance to Striga in the Sudan
Sorghum. Credit AATF

Sorghum. Credit AATF

Sorghum is one of the most important crops in Africa, but it faces challenges from drought and the devastating parasite Striga or witchweed. Striga affects an estimated 40% of arable savannah land and the livelihoods of more than 100 million people in Africa.[1]

One of the first commercially released hybrid sorghum varieties, Hageen Durra 1, was developed and tested in Sudan by the International Crops Research Institute for the SemiArid Tropics (ICRISAT) in the early 1980’s. Hageen Durra 1 was both drought tolerant and high yielding producing 50%–100% higher yields than traditional varieties. Drought tolerant hybrid varieties were later developed in Niger that produced yields 4–5 times the national average. Some of the most significant advances were made in the 1990’s with the development of Striga tolerant hybrid sorghum varieties.

Sorghum breeder Gabisa Ejeta and team used several breeding approaches to identify genes for Striga resistance then used these in crosses with locally adapted and modern sorghum varieties.[2] The new Striga tolerant sorghum varieties were widely adapted to different African environments and are now grown from Sudan to Zimbabwe. Sorghum productivity was also enhanced through the introduction of an integrated Striga management system that included weed resistance, soil fertility improvement and water conservation.[3] In 2009, Gabisa Ejeta was awarded the World Food Prize for his seminal achievements in improving the livelihood opportunities of African sorghum growers.[4]

References
  1. [1] Gressel, J, Hanafi, A, Head, G, Marasas, W, Obilanae, AB, Ochandaf, J, Souissig, T & Tzotzos, G 2004, ‘Major heretofore intractable biotic constraints to African food security that may be amenable to novel biotechnological solutions’ Crop Protection, vol. 23, no. 8, pp. 661–689.
  2. [2] Ejeta, G 2007 ‘Breeding for Striga resistance in sorghum: Exploitation of an intricate host–parasite biology’ Crop Science vol. 47, no. S3, pp. S216–S227.
  3. [3] Ejeta, G & Gressel, J (eds.) 2007, Integrating new technologies for Striga control. Towards ending the witchhunt, World Scientific Publishing, Singapore.
  4. [4] Food and Agriculture Organisation of the United Nations (FAO) 2011, ‘Biotechnologies for Agricultural DevelopmentProceedings of the FAO International Technical Conference on “Agricultural Biotechnologies in Developing Countries: Options and Opportunities in Crops, Forestry, Livestock, Fisheries and Agro-industry to Face the Challenges of Food Insecurity and Climate Change (ABCD-10), FAO, Rome
Case study 3: Hybrid Cassava and Cassava Mosaic Disease in Uganda
A local variety of cassava showing signs of African Cassava Mosaic Virus. Credit IITA

A local variety of cassava showing signs of African Cassava Mosaic Virus. Credit IITA

Cassava is grown in more than 40 countries in sub-Saharan Africa and Nigeria is now the largest producer of cassava in the world. Cassava production in Africa, however, is severely threatened by cassava mosaic disease (CMD). In the 1970’s the International Institute of Tropical Agriculture (IITA) developed high yielding mosaic disease resistant cassava varieties by a process known as ‘Tropical Manjioc Selection’ (TMS) that draws on earlier approaches crossing the disease resistant Ceara rubber x cassava hybrid with high-yielding West African selections.[1] These TMS varieties increased cassava yields by 40% without the use of fertiliser.[2]

In the mid-1990’s CMD appeared in a new, more virulent form in Uganda known as East African cassava mosaic virus. The epidemic spread south along a broad “front” at a rate of approximately 20 km per year subsequently reaching neighbouring countries and beyond. CMD is not only highly contagious, but the symptoms are severe. Infected crops in Uganda suffered a 55%-87% yield loss and in just 6 years, 80% of Uganda’s cassava crop was destroyed. Cassava was all-but abandoned in Uganda, contributing to food insecurity in the late 1990s.[3]

IITA, the National Root Crops Research Institute and the Root and Tuber Expansion Program have undertaken a project to conduct both demonstrations and on-farm trials in Uganda and Nigeria. From more than 2,500 trials, 12 disease resistant TMS varieties have been released. These have multiple resistance and tolerance to CMD along with other yield-damaging pests such as bacterial blight disease, anthracnose disease, green mite and mealybug. They are high-yielding and suitable for the food industry and livestock feed. Yields of these TMS hybrids range from 20 tonnes to 50 tonnes per hectare or 40% to 100% higher than local varieties.[4]

References
  1. [1] Nweke, F 2009, ‘Controlling cassava mosaic virus and cassava mealybug in Sub-Saharan AfricaInternational Food and Policy Research Institute (IFPRI) Discussion Paper 00912, IFPRI, Washington, DC.
  2. [2] Nweke, F 2009, ‘Controlling cassava mosaic virus and cassava mealybug in Sub-Saharan AfricaInternational Food and Policy Research Institute (IFPRI) Discussion Paper 00912, IFPRI, Washington, DC.
  3. [3] Faquet, C & Fargetter, D 1990, ‘African Cassava Mosaic Virus: Etiology, Epidemiology, and ControlPlant Disease, vol. 74, no. 6, pp. 404-411.
  4. [4] Dixon, AGO, Okechukwu, RU, Akoroda, MO. Ilona, P, Ogbe, F, Egesi, CN, Kulakow, P, Ssemakula, G, Maziya-Dixon, B, Iluebbey, P, Yomeni, MO, Geteloma, C, James, B, Eke-Okoro, ON, Sanni, L, Ntawuruhunga, P, Tarawali, G, Mahungu, N, Lemchi, J, Ezedinma, CI, Okoro, E, Kanju, E, Adeniji, AA & Nwosu, K (no date), IITA Improved Cassava Variety Handbook, International Institute of Tropical Agriculture (IITA), available online: <http://www.iita.org/c/document_library/get_file?uuid=8e05fd78-7344-4a97-aa2a-e99af14bd3ac&groupId=25357> [6 July 2015].