Winning the battle against cassava mosaic disease
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|Extending the control of cassava mosaic disease|
Millions of farmers in Uganda and Tanzania are fighting the cassava mosaic disease (CMD) pandemic using new, resistant cassava varieties and other control methods. Government organisations and NGOs are multiplying and distributing these CMD-resistant varieties on a huge scale. And, new options, such as selecting clean planting material and identifying varieties resistant to the whiteflies that spread the disease, are also proving useful. Leaflets and a guide that describe CMD control strategies, developed by Ugandan and Tanzanian partners and validated by farmers, are available in different languages including English, Swahili and Luganda. The solid, scientific knowledge gained about control strategies and how they work will be invaluable to other countries threatened by CMD, such as Rwanda, Burundi, DR Congo, Republic of Congo, Gabon and Nigeria.
Project Ref: CPP24:
Crop Protection Programme
Relevant Research Projects:
Closely associated projects
The Natural Resources Institute, University of Greenwich, Central Avenue, Chatham Maritime, Kent, ME4 4TB, UK. Lead person: Dr Richard Gibson [email: firstname.lastname@example.org]. Contact persons: Dr John Colvin [email: email@example.com].
Cassava mosaic disease (CMD), caused by whitefly-borne cassava mosaic begomoviruses [geminiviruses], is the most important disease affecting cassava in Africa. In particular, a natural recombinant of East African cassava mosaic virus (EACMV) with African cassava mosaic virus(ACMV), EACMV-Ug [also known as UgV for Uganda variant], identified in Uganda, has been linked with a pandemic first recognised in Uganda in the late 1980s, spreading to most of the country and to neighbouring Kenya in the 1990s, and since spreading to the Lake Zone of Tanzania, Rwanda, Burundi, DR Congo, Republic of Congo and Gabon. It even threatens Nigeria, the major producer of cassava in Africa. The pandemic is associated withEACMV-Ug causing a particularly severe disease, especially in the presence of ACMV, and increased numbers of the whitefly, Bemisia tabaci, vector of cassava mosaic geminiviruses in Africa. The enhanced vector population and high virus titres of EACMV-Ug and ACMV allowing easy virus acquisition and therefore infection appear to be the main forces driving the spread of the pandemic. The increased whitefly numbers have been associated with populations with a particular DNA fingerprint, with cassava infected by EACMV-Ug being more suitable for whitefly multiplication and with increased use of some CMD-resistant cassava varieties which inadvertently are very good whitefly hosts.
The main strategy to control the pandemic has been the development of CMD-resistant cassava varieties by national and international programmes, particularly the Ugandan National Cassava Programme (UNCP) based at Namulonge Agricultural and Animal Production Research Institute (NAARI), the Tanzanian Root and Tuber Research Program (TRTRP) at Ukiriguru Agricultural Research Institute (ARI) and at Maruku ARI and the International Institute of Tropical Agriculture (IITA). Project outputs include validating these varieties as a control strategy, understanding and exploiting how these varieties resist CMD through resistance to getting infected, recovery from infection and a high likelihood that cuttings taken from infected plants, particularly from upper parts where recovery has occurred, will revert (reversion) to give disease-free plants, all factors combining to achieve disease-free crops. The project, working with farmer groups in Uganda and Tanzania over the last several years, has identified preferred CMD-resistant varieties, monitored and evaluated different ways of distributing planting material to farmers and proposed improvement. It has also researched selection of clean planting material of CMD-susceptible varieties, especially when protected by interplanting amongst CMD-resistant varieties. Recently, whitefly-resistant cassava clones have been identified within advanced CMD-resistant germplasm; combining these characters may achieve more durable resistance. Leaflets and a guide validated by farmers and describing control strategies for CMD have been developed by UNCP and TRTRP in different languages including English, Swahili and Luganda and distributed at farmer meetings.
Main commodity: Cassava.
Whitefly-borne viruses, particularly geminiviruses belonging to the genus Begomovirus, are the causal pathogens of diseases of many warm temperate, semi-tropical and tropical climate crops. Whilst a few affect staple food crops such as cassava, beans and sweet potato, many also affect higher value horticultural food crops like tomato, peppers and cucurbits. The latter are also important to poor people because they provide cash and are an important source of vitamins and other essential dietary requirements. The control strategies for cassava mosaic diseases provided by project outputs may also be tailored to support control strategies for whitefly-borne viruses affecting these crops.
The primary aim of the project outputs are to restore and then sustainably increase productivity of cassava following the CMD pandemic. This achievement needs to be linked to postharvest outputs generated by CPHP projects on cassava [R6504; R7418, R8268, R6332, R6316 and R7495]. In this manner, increased productivity will be sustained by increased markets for fresh and processed cassava. In this manner, the pre- and postharvest outputs will gain positive feedbacks from each other.
Value could be added to project outputs by clustering them with those on the control of other whitefly-borne viruses. These include outputs on another whitefly-borne virus of cassava, Cassava brown streak virus [projects R8227, R7563], also Sweet potato chlorotic stunt virus affecting sweet potato [projects R8457, R8243] and Tomato leaf curl virus on tomato [projects R8425, R8247].
More limited value could also be obtained by clustering with outputs of other IPM projects and with one on the evolution of begomoviruses [R8222].
There are also numerous national and regional programmes involved in the dissemination of improved cassava production methods. These include the Cassava Mosaic Pandemic Mitigation in East and Central Africa Project, co-ordinated by IITA and financed by USAID-OFDA, the Crop Crisis Control Project (C3P) led by a Catholic Relief Services-IITA consortium (http://c3project.iita.org/), and the Pre-emptive Management of Cassava Mosaic Disease in Nigeria Project, and programmes for the multiplication and distribution of superior planting materials and evaluation of germplasm for cassava in Mozambique. Many of these programmes are building on achievements made through DFID-funded work falling under the CPP projects indicated above.
How the outputs were validated:
Outputs were validated by different groups of people in several ways:� By farmer groups conducting on-farm trials assessing different management strategies, group meetings assessing the usefulness of leaflets, guides etc. The trials were generally suggested by scientists to the farmers who then agreed they were keen to be involved and provided the practical elements of each trial. Individual trials generally included an element of demonstration and often had limited replication; adequate replication was achieved by combining the results of several trials. Farmer groups comprised smallholder farmers, e.g., few had machine-powered implements, growing most of their own food and having a small surplus for sale. Whilst farmer groups were generally gender balanced including women leaders, it should be appreciated that farmers involved in group activities were generally the richer, better educated and more active members of the community. Groups represented both Christian and Moslem religions.
� By national scientists conducting on-farm multilocational, on-station trials and screenhouse trials of different control practices for CMD including comparing different varieties and management practices. Trials were replicated, fully-randomised complete block designs generally repeated for at least two cropping cycles.
� By peer international scientists providing external reviews of project outputs when published as Final Technical Reports and peer reviews of project methods and analyses prior to publication of project results in international scientific journals. These have included Advances in Virus Research, Virology, Plant Pathology, and Biocontrol Science and Technology. Project outputs have also been subjected to peer scrutiny when disseminated through presentations at regional [e.g., 9th Triennial Symposium International Society of Tropical Root Crops – Africa Branch and 7th African Crop Science Society Conference] and international [e.g., 2nd European Whitefly Symposium, Cavtat, Croatia – 5-9 October 2004, 6th Intrtl. Sci. Meeting Cassava Biotechnology Network, and IX International Plant Virus Epidemiology Symposium, April 4 – 7, 2005. Lima, Peru].
Where the Outputs were Validated:
Outputs were validated for the following circumstances:
� By smallholder farmers in Central [Mpigi, Luwero and Iganga districts] and north-eastern [Apac and Lira districts] Uganda and in north-eastern Tanzania [Kagera Region] using manual tools for cultivation, clearing the land by slashing and burning. These are rain-fed farming systems in agro-ecological environments in which complete forest cover or incomplete forest cover plus tall grass would be the natural climax vegetation and the environment would be wet to semi-arid. Trials were done mainly during 2000 – 2004; validation of leaflets and guides were done mainly during 2003 – 2005.
� By on-station trials done during 2000 – 2004, building on earlier DFID and other donor funded trials since 1991 at Namulonge Agricultural and Animal Production Research Institute located some 30 kms north of Kampala in Uganda in rainfed systems where humid forest would be the climax vegetation. Trials were planted on research fields previously fallowed, generally treated with herbicide [Round-up] and ploughed by tractor; subsequent management involved manual hoeing to control weeds and manual harvest.
� By peer review of scientific papers mainly by journals published in Europe/ N. America and therefore probably mainly by scientists from those areas.
Who are the Users?
The outputs are currently being used by:
� Millions of smallholder farmers in Uganda and tens, perhaps hundreds of thousands of smallholder farmers in the Lake Zone of Tanzania. In particular, farmers are growing CMD-resistant varieties developed and distributed as part of project outputs widely promoted throughout these regions. To a more limited extent, farmers are also selecting clean planting material.
� By government organisations [training institutes, prison farms, district extension officers, research scientists] and NGOs [e.g., Actionaid, Concern, RUDDO, World Vision] involved in assisting smallholder farmers especially in the Lake Zone of Tanzania [see diagram below]. These organisations are multiplying and distributing CMD-resistant varieties developed as part of project outputs and also using training protocols and training materials (leaflets, guides) as part of their extension activities.
� By scientists elsewhere in the region and in Africa as a basis for control strategies for CMD
Figure: Some of the organisations in the Lake Zone of Tanzania using project outputs.
|Where the outputs have been used:
Project outputs are primarily being used by farmers throughout Uganda and in north-western Tanzania. The CMD pandemic affected almost all Uganda by 2000. Project-developed strategies are now widely used throughout the country although dissemination activities are reducing.
The pandemic has affected Tanzania only since about 1998. Entering through the Lake Zone, it is still spreading and many farmers still need training and to receive CMD-resistant varieties. Training is being provided in NW Tanzania only and to four different groups: i) district and Norwegian People’s Aid (NPA) extension personnel, ii) farmer groups in farmer field schools (FFS), iii) FFS group facilitators and field officers, and iv) districts and prison agricultural officers from selected districts and stations in Tanzania. The diagram above illustrates the partners in this exercise and their locations in the Lake Zone. In particular, RUDDO Caritas is funded by the NPA to train and provide planting material to farmers in refugee-affected areas of Biharamulo and Ngara districts of Kagera region; GTZ, Concern and ActionAid have begun to extend into neighbouring Kigoma Region.
Knowledge outputs disseminated regionally through publications in international and regional journals and at international and regional scientific meetings are also being tailored by national scientists in other countries e.g., Rwanda, DR Congo, and disseminated to their farmers.
Scale of Current Use:
Probably millions of farmers in Uganda are now using CMD-resistant varieties. Surveys of farmers’ fields in six districts [Iganga, Kamuli, Luwero, Masindi, Mpigi and Mukono] by the National Cassava Programme indicate plantings of CMD-resistant varieties increased from 0% in 1990 – 1994 to reach 35% in 2003 by which time most Ugandan farmers were growing some resistant varieties, though most also maintained crops of their traditional landraces.
In Tanzania, few CMD-resistant varieties had been distributed anywhere by 1998. Material is now being multiplied and distributed to farmers in the Lake Zone, especially to farmer groups within Ngara and Biharamulo districts using funds provided by Norwegian Peoples’ Aid to assist farmers in refugee-affected areas. The two tables below indicate the scale and achievements of the operation.
Table: CMD-resistant planting materials multiplied under NPA-funding and available for distribution as identified in a survey in November 2004
Table: Cassava multiplication at Nyakahura ward in Biharamulo 2003/2004 seasons
Policy and Institutional Structures, and Key Components for Success:
In both Uganda and Tanzania, cassava is one of the most important food crops, CMD was identified as having a major impact on livelihoods and had been identified by farmers, extensionists, researchers and policymakers in agricultural government ministries as high priority. Consequently, there was a strong national commitment to deal with the CMD pandemic.
There was also a strong, integrated and innovation systems approach to the pandemic involving partnerships linking national programme activities with regional and international efforts. Additionally, the project funded an NRI staff member based in Uganda co-employed by the International Institute of Tropical Agriculture. As well as conducting its own research and breeding programme to combat the CMD pandemic, IITA also manages more extensive regional and country-wide programmes on cassava rehabilitation, notably through the regional CMD Pandemic Mitigation Project, currently targeting Kenya, Tanzania, Rwanda and Burundi, and through its participation in the C3P project, which in addition to the above countries also works in Uganda and DR Congo. The close linkages achieved by sharing staff also assisted in ensuring that project outputs were jointly exploited in these large rehabilitation programmes.
Long-term funding provided by DFID, for Uganda since the early 1990s, was maintained in an almost continuous stream until 2005. Gatsby and other donors also contributed in a well-co-ordinated manner. This gave researchers opportunity to conduct the necessary research, yet maintain limited links with farmers so as to ensure relevance of research and quality of training and materials, particularly planting material.
A major success of the project in Tanzania was to establish a close linkage with Norwegian People’s Aid and its infrastructure already in place, its links with NGOs and its funds enabled an extensive and high quality rehabilitation of cassava production in Ngara and Biharamulo districts through extensionists of NPA and NGOs to be achieved speedily, researchers maintaining quality control of training whilst being sheltered from the day-to-day business of farmer training.
In a somewhat similar but also somewhat different manner, a new institutional arrangement, the National Network of Cassava Workers (NANEC) was developed in Uganda and funded by Gatsby Charitable Trust. This also achieved a similar flow of up-to-date information from researchers to extensionists whilst also shielding them from direct farmer training. As well as being created de novo, NANEC provided a national service; however, Tanzania has a more decentralised extension system with a strong zonal administrative structure.
Figure provided by Dr Anton Bua, Head of Ugandan National Cassava Programme
Direct and Indirect Environmental Benefits:
The technologies developed are largely neutral in their effects on the environment. No pesticides or genetically manipulated crops are involved in the outputs. No major changes in cropping practice are involved. Land cover may be increased by the more rapid growth of healthier crops and more vigorous varieties, reducing erosion. Adoption of the outputs may lead to increased land area cropped by cassava but this may indirectly be beneficial because cassava has a greater food output/unit land than most crops so this will lead to less land having to be cropped, allowing longer fallows.
Adverse Environmental Impacts:
No. None have been identified to date and no adverse environment impacts are to be expected from a shift from CMD-susceptible varieties to CMD-resistant varieties. Selecting clean planting material is also unlikely to have adverse effects as is the limited amount of roguing needed in a CMD-resistant variety.
Coping with the Effects of Climate Change, or Risk from Natural Disasters:
YES. Poor people turn to cassava when climate change or natural disasters occur because it is has the capacity to yield large amounts of food from a small amount of land and within a short time (3 mths; faster than most other staple food crops). Cassava is also very resilient in the face of erratic rainfall because of its indeterminate growth, unlike, e.g., maize. NGOs have begun to provide cassava planting material for refugees. Under such circumstances, it is vital that high-yielding, disease-resistant varieties are provided, the plant material is selected from disease-free parents and farmers are trained to rogue diseased cuttings.
Relevant Research Projects, with links to the