A new variant of a cassava disease is affecting large parts of East Africa, especially in the area's Great Lakes Region, putting a crucial source of food and income at risk, according to the UN Food and Agriculture Organization. FAO experts say Cassava Brown Streak Disease (CBSD) is on the verge of becoming an epidemic, and have called for an urgent increase in funding, research, training, surveillance and other measures to help farmers and breeders. The appearance of the disease in previously unaffected areas, and the lack of continued funding for research and development work to address CBSD in the region, have added to the threat already presented by Cassava Mosaic Disease (CMD). In Rwanda, a surveillance analysis conducted by the National Agricultural Research Institute in 2010 showed a 15.7 percent rate of infection on local varieties and 36.9 percent in improved varieties.
"None of the cassava varieties currently being distributed to farmers seem to be tolerant to the effects of CBSD. We urgently need to get information on the extent and severity of the outbreak, and to support investments to identify disease-tolerant varieties and coping strategies for farmers," said Jan Helsen, leader of FAO's European Union-funded Regional Cassava Initiative in Eastern and Central Africa.
One of the challenges facing those who are trying to stem the spread of CBSD is timely detection of the disease. "The disease manifests itself in different ways depending on local conditions. In some cases it shows symptoms only on the roots. An apparently healthy plant may be found to have spoiled roots only when harvested, with obvious consequences for food security," Helsen explained. Cassava can account for as much as a third of the total calorie intake for people in countries such as Burundi, Rwanda, Uganda or DRC. "Thanks to the foresight of, and the scientific support from, the International Institute of Tropical Agriculture (IITA), efforts are underway to understand the epidemiology of the disease, but more support will be needed for this work, and to select and bring on CBSD-tolerant varieties," Helsen added.
Short-term measures needed to tackle CBSD include stepping up disease surveillance and conducting regular inspections; increasing the sensitization of communities to the threat of CBSD; and using hands-on training for farmers, like FAO's farmer field schools, to introduce community-based practices to prevent the introduction or spread of the disease, such as the removal of infected plants. Recommended measures also include banning the distribution of infected plants between districts and zones, and, in the event of infection, using coping strategies such as the early harvest of cassava, before symptoms appear and significant damage can be done.
Since around 2006, FAO and the Catholic Relief Services (CRS) have implemented two regional cassava projects, funded respectively by the European Union and the Bill and Melinda Gates Foundation, to support vulnerable farmers affected first by CMD and now by CBSD. The projects have provided access to clean, or virus-free, planting material. The projects aim to develop capacity in disease preparedness and strengthen the resilience of farmers to outbreaks of both diseases. "Fortunately, there are now eight varieties under development by IITA and its national partners in the region which are resistant to Cassava Mosaic Disease and which show some level of tolerance to CBSD. Under existing program arrangements, these varieties could be made widely available in the next 18-24 months, assuming that resources can be identified to support multiplication and distribution activities," said Helsen. Helsen says National Cassava Steering Committees have been set up to manage the response to the disease, but they need more time and funds to ensure that some of the CBSD-tolerant varieties in the pipeline can be multiplied and made available across the region.
More extensive surveillance will be carried out in Rwanda again this year, along with Burundi and the DRC, which will give a more complete picture of the occurrence and spread of the disease. To help raise awareness of the impact of the disease, FAO and CRS are currently undertaking a rapid survey on the impact of CBSD on household food security across the region.