Experts declare war on cassava viruses in Africa

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©IFAD/Susan Beccio 
Wafaa El-Khoury, Senior Technical Advisor on Agronomy at International Fund for Agricultural Development (IFAD) just returned from the Strategic Meeting of The Global Cassava Partnership for the 21st Century. This year’s theme was “Declaring War on Cassava Viruses in Africa”, an important topic since cassava experts are reporting new outbreaks and an increased spread of Cassava Brown Streak Disease (CBSD). According to experts the rapidly multiplying plant virus could cause a 50 per cent drop in production of a crop that provides a substantial source of food and income for 300 million Africans. El-Khoury highlights that close cooperation between the research, development and donor communities is needed to keep the disease under control in the already affected areas of East Africa while ensuring the prevention of its entry into West Africa. Here are her takeaways from the meeting, and recommendations for the future.

Q: How is the topic you discussed at the conference relevant to IFAD and its operations?

Cassava is among the most important crop for the livelihoods of IFAD’s beneficiaries mainly in Africa, but also in Asia and in Latin America. IFAD loans and grants portfolio includes substantial investments in the development of the cassava value chains as well as in ensuring food security for the most vulnerable people, especially in regions with difficult environmental conditions and in areas at risk of effects to climate change. As you may know cassava has been seen as a stable and resilient crop in the face of effects of climate change. The occurrence of a virus disease would directly affect IFAD’s operations in these countries reducing the chances of success in value chain enhancement activities, and also impact food security and nutrition related activities. Cassava Brown Streak Disease (CBSD) is a virus disease (2 active viruses) severely infecting all cassava varieties that have been newly developed resistant to the Cassava mosaic disease (CMD), another disease that has been devastating East and Central Africa for over a decade. CBSD is transmitted through the whitefly vector and through cuttings used for vegetative propagation. The cassava experts are reporting new outbreaks, and an increased spread of the CBSD epidemic in East Africa is worrying and the concern would increase substantially if the virus spreads to West Africa and even other continents. IFAD should play an active role together with the international research and development community to resolve the problem as soon as possible, and I will give a more detailed perspective in the text below.

Q: What do you think has changed for the farmers who have been dealing with such threats over the years?

©IFAD/Gerard Planchenault
It is true that farmers have had to deal with biotic and abiotic threats throughout history, and farmers have dealt with them in various ways, mainly through the selection and multiplication of best landraces that could survive these threats. Traditionally farmers have selected crop populations with the most stable yield and not necessarily the crop with the highest yield. Today farmers are under pressure to increase productivity and production for food security and income generation. This is achieved mainly through crop intensification with changes in cultural practices and cropping patterns, often with a reduction of genetic diversity across landscapes, but also with the cultivation of new crops in areas previously considered not adapted to their growth. These developments have been accompanied by an increase in the movement of human beings and genetic material across countries and continents, and by a changing climate affecting the populations of pests, diseases and their interaction with host plants. All these factors are resulting in an increasing global incidence of emerging infectious diseases. Studies have shown that these are mainly the result of pathogen introductions into new areas (56% of cases), weather related (25% of cases), changes in farming techniques and systems (9% of cases), changes in vector populations (7% of cases ) or genetic recombination of the pathogen or habitat disturbances (Anderson et al 2004).

Around 50% of these emerging infectious diseases are viruses and they can quickly get established and spread to epidemic levels. Research has shown that emerging infectious viruses developing into disease epidemics are consistently linked to human-induced changes in agricultural production systems.

African farmers have in the past decades witnessed a series of epidemics that have devastated their staple crops. Cassava Brown Streak Disease (CBSD) is presently still restricted to East Africa but the research and development community have serious concerns that it will soon move to Central and West Africa devastating the main cassava-producing areas. The problem is further complicated through the emergence of new populations of the whitefly vector that are highly prolific with very high multiplication rates, resulting in high disease transmission rates and causing severe crop damage through their direct feeding on the plant. The increased vector populations are expected to be favoured through the effect of climate change in Africa. CBSD is a disease that produces limited leaf symptoms which makes it difficult to spot and eliminate infected plants early in the growing season, but at harvest time, severe root symptoms are observed (necrosis, browning of the roots such that they are not fit for processing or eating).


Q: What should we in IFAD be doing differently to equip our beneficiaries to better deal with the threats of cassava viruses? 

Through its loan and grants IFAD has been extremely active in the past decades in the promotion of cassava productivity in Africa. Not only did it promote the introduction of new highly productive varieties adapted to the needs of the farmer and markets, it has supported farmers and women in postharvest cassava transformation and value additions. Through its grants system, IFAD’s support was crucial to the pan-African control of the devastating cassava mealy bug pest through the environmentally and eco-system friendly method of biological control.

However, with the continuous changes in agricultural production systems, natural landscapes and global climate, the risk of pandemics is expected to increase. Development interventions, including IFAD’s interventions should accordingly ensure the resilience of farming systems ahead of the emergence of the problem. The response at the onset of the epidemic should be holistic, based on multiple interventions with considerations at landscape levels beyond the farm level. Considerations should also be given to awareness raising and policy interventions at the national level and beyond. The disease control should never rely on one single solution such as only the introduction of resistant varieties but should include various disease management options and major elements of capacity building to ensure sustainability of interventions and capacity of farmers and national institutions to respond to similar future shocks. Among possible IFAD interventions that go beyond research is through its rural finance activities and its linkage to the private sector to support farmers in accessing virus free clean planting material, often a limiting factor for farmers while it is one of the most critical disease management practices. Capacity building of farmers and farmer organization in identifying the disease and establishing community-based phyto-sanitation, which has proven effective in disease management could also be part of IFAD’s interventions. IFAD could also play a critical role in institutional capacity development and support in national coordination for contingency planning and response to similar emergencies. IFAD could also fund research on multiple management solutions to CBSD as well as on understanding the future risks and mitigation strategies for the emergence of pests and diseases of food security crucial crops as cassava.

Q: What are your three most important takeaways that you would like to share with colleagues/partners? 
  1. Emerging trans boundary epidemics affecting staple crops can only be managed through international cooperation involving the research, development and donor communities. They would require also political will for action and hence a lot of advocacy and awareness raising with the national, sub-regional and regional levels that would influence relevant policy and decision-making bodies.
  2. Pandemics –whether affecting humans, animals or crops, are becoming more frequent and more devastating. Learning from previous epidemics is critical to assess the potential risks, and enhance preparedness and effective response at the national, regional or global levels. Critical elements to achieve such response is the preparation of contingency plans for quick and effective interventions, vigilant surveillance systems, functional seed systems and proper support to farmers and their organizations for efficient field level response. Awareness and policy support are pre-requisites for the success of any intervention. There was a general agreement at the meeting that CBSD elimination is not possible, especially where it is now endemic in East Africa. In this case management is critical, especially through the control of the vector and through use of clean propagative material. It is however important to try to prevent the entry of CBSD into West Africa and the other continents through vigilant and systematic surveillance, which allows for early detection and eradication upon its entry to new areas and before it grows to epidemics.
  3. There is still a lot of missing scientific information about CBSD and other potentially devastating cassava virus diseases to be able to manage them properly in the field. More research is still needed on topics covering the resistance and tolerance of cassava improved varieties and landraces to CBSD, its distribution within the plant, transmission through whiteflies and through propagative material, and the effect of plant nutrition on disease expression and severity. In all cases, the disease management strategies should depend on combined interventions through the use of virus-free planting material, elimination of infected material from the field, sanitation and other cultural practices, host plant resistance (to virus or whitefly vector), and very importantly the integrated management of the whitefly vector (integrated pest management, IPM).



Watch video on CBSD from CIAT