A viral disease known as Cassava Brown Streak Disease (CBSD) is posing a serious threat to cassava cultivation across Sub-Saharan Africa, raising concerns about food security for millions of people who depend on the crop for both nutrition and income.
Cassava is one of the most important staple crops in Africa because it can grow in drought-prone areas and poor soils, making it a vital food security buffer for vulnerable populations. However, the spread of CBSD could significantly reduce production and undermine this resilience.
The disease causes necrosis (rot) in cassava roots, often leading to complete crop loss. In many cases, symptoms appear only when the crop is harvested, meaning farmers may not detect the infection until it is too late.
Importance of Cassava in Africa
Cassava is widely cultivated in Africa because it is highly adaptable to harsh environmental conditions. It plays a crucial role in ensuring food security, rural livelihoods, and economic stability across the continent.
Cassava serves as:
- a staple food for millions of households
- a source of income for smallholder farmers
- a drought-resilient crop during periods of food shortage.
Because of these characteristics, cassava is often considered a “food security crop” in many African countries.
Study Findings: Vast Areas at Risk
A study published in the East African Journal of Science Technology and Innovation highlights the potential scale of the problem.
The research estimates that:
| Indicator | Estimate |
| Land suitable for cassava cultivation in Africa | 54.6% of the continent |
| Area suitable for cassava cultivation | ~16.2 million sq km |
| Area at risk of CBSD spread | ~33.7% of Africa |
| Land threatened by the virus | ~10.2 million sq km |
Although the virus is currently restricted to Africa, scientists warn that it could expand into West Africa, which includes some of the largest cassava-producing countries such as Nigeria and Ghana.
Historical Spread of the Virus
CBSD was originally confined to coastal areas of Tanzania and Mozambique, where it remained largely endemic for more than 70 years.
However, in recent decades the disease has spread to other parts of East and Central Africa, including Uganda, raising concerns that the virus could continue spreading across the continent.
Role of Whiteflies in Disease Spread
The main vector responsible for transmitting CBSD is the Bemisia tabaci, commonly known as the whitefly.
Whiteflies exist as a complex group of genetically distinct populations. Certain populations in sub-Saharan Africa, particularly the Sub-Saharan Africa 1 and 2 groups, are especially effective at spreading the virus.
According to research led by Geofrey Sikazwe from Stellenbosch University, these whitefly populations are present in large densities across East and Central Africa.
Their populations have been increasing due to:
- climate change
- agricultural intensification
- favourable environmental conditions.
Agricultural Practices Contributing to the Spread
Farming practices also play a role in spreading the disease. Many smallholder farmers reuse cassava cuttings from previous harvests as planting material.
If the parent plant is infected, the virus can easily spread to the next generation of crops.
Another issue is the lack of formal clean seed systems in many African countries. In contrast, countries such as Thailand, the world’s largest cassava exporter, distribute certified disease-free planting material through structured agricultural systems.
Interaction with Other Cassava Diseases
Many cassava varieties were previously developed to resist Cassava Mosaic Disease (CMD).
However, several of these improved varieties turned out to be susceptible to CBSD, creating a large reservoir of vulnerable crops and allowing the virus to spread more easily.
Climate Change and Disease Expansion
Climate change is also influencing the spread of CBSD.
Changes in temperature and rainfall patterns can affect both:
- cassava cultivation suitability
- whitefly population dynamics.
Warmer conditions may increase the distribution of whiteflies, allowing the virus to spread into new regions.
However, scientists note that the movement of infected planting material through informal trade and farmer exchanges remains the most immediate driver of outbreaks.
Research and Breeding for Resistance
Scientists have identified natural resistance to CBSD in cassava varieties from South America, where cassava originally evolved.
These genetic resources are being shared with breeding programmes across Africa and other regions.
Dual-resistant cassava varieties—capable of resisting both CBSD and CMD—are currently being tested in several countries including:
- Democratic Republic of Congo
- Tanzania
- Uganda
- Mozambique
- Malawi
- Cameroon
- Zambia
Testing is also underway in countries outside Africa, including Brazil and Vietnam.
Ethiopia: A Rare Exception
Interestingly, Ethiopia remains one of the few countries in East Africa where CBSD has not yet been reported.
Although whiteflies are present in Ethiopia, they mainly affect other crops, and field studies indicate that virus transmission through whiteflies spreads only about 17 metres per season, limiting rapid spread under certain conditions.
Climate Adaptation Potential of Cassava
Despite the disease threat, cassava may still play an important role as a climate-resilient crop.
Climate models suggest that rising temperatures could expand areas suitable for cassava cultivation in drought-prone regions, making it a possible alternative to crops such as:
- maize
- sorghum.
Strategies to Protect Cassava Production
Experts emphasize that safeguarding cassava will require coordinated action.
Recommended measures include:
- improved phytosanitation practices
- use of virus-free planting materials through tissue culture
- development and distribution of disease-resistant varieties
- strengthening clean seed systems
- establishing farmer surveillance networks for early detection
- managing whitefly populations through integrated pest management techniques, including intercropping and the use of natural predators.