Cassava Brown Streak Disease Threatens Africa’s Staple Crop

A viral disease causing rot in cassava roots is raising alarm across sub-Saharan Africa, threatening a staple crop relied upon by millions for food security and income. Cassava, prized for its tolerance to drought and poor soils, serves as a critical safety net for vulnerable households. However, scientists warn that the spread of Cassava Brown Streak Disease (CBSD) could severely undermine this resilience.

Impact of Cassava Brown Streak Disease

CBSD causes necrosis in cassava roots, often leading to total crop loss. The disease can remain hidden until harvest, when farmers discover discoloured, inedible roots. This delayed visibility worsens economic losses and food shortages.

Although confined to Africa, CBSD remained largely endemic for over 70 years along coastal regions of Tanzania and Mozambique. It has since spread to Uganda and parts of East and Central Africa. Researchers now caution that West Africa — home to major cassava producers such as Nigeria and Ghana — could face significant risk if preventive measures are not strengthened.

Extent of Risk Across the Continent

A recent study published in the East African Journal of Science, Technology and Innovation estimates that 54.6 per cent of Africa’s landmass — around 16.2 million sq km — is suitable for cassava cultivation. Simultaneously, approximately 33.7 per cent of the continent, or 10.2 million sq km, is at risk of CBSD spread.

Scientists note that environmental suitability, host availability, and informal trade in infected planting materials are key factors influencing disease expansion. Climate change, including rising temperatures and altered rainfall patterns, further increases vulnerability in some regions.

The Whitefly Vector and Farming Practices

CBSD is primarily transmitted by the whitefly Bemisia tabaci, particularly the Sub-Saharan Africa 1 and 2 genetic groups, which occur in high densities in East and Central Africa. Agricultural intensification and climatic shifts have amplified their populations.

Smallholder farming practices also contribute to transmission. Many farmers reuse cuttings from previous harvests, unknowingly perpetuating infection. Weak formal seed systems in much of Africa contrast with structured distribution models in countries such as Thailand, where certified disease-free planting material is standard. Additionally, some high-yield varieties bred to resist Cassava Mosaic Disease proved vulnerable to CBSD, expanding the pool of susceptible plants.

Important Facts for Exams

• Cassava Brown Streak Disease causes root necrosis and severe yield losses.
• Bemisia tabaci whiteflies act as the primary vector of CBSD.
• Cassava is a drought-tolerant staple crop across sub-Saharan Africa.
• Climate change can influence pest populations and crop disease spread.

Breeding Resistance and Future Outlook

Encouragingly, researchers have identified natural resistance to CBSD in South American cassava varieties. Germplasm is being incorporated into breeding programmes in several African countries, including the Democratic Republic of Congo, Tanzania, Uganda and Mozambique. Dual-resistant varieties capable of withstanding both CBSD and other viral threats are under evaluation. Scientists emphasise that strengthening clean seed systems and regional surveillance remains essential to safeguarding Africa’s vital cassava economy.