Cassava Brown Streak Disease

Leaf symptoms, when present, appear as a yellow chlorosis along the veins or in blotches between the veins, and brown streaks can develop on the stems. The most important and damaging symptom, however, is internal: a dry, brown, corky necrosis within the storage roots, sometimes with surface constrictions. Because roots can be badly affected while foliage looks relatively healthy, the disease is often underestimated until harvest.

The cassava brown streak viruses are transmitted by whiteflies and are carried over in infected cuttings used for propagation. As with other cassava virus diseases, planting cuttings from infected plants introduces the virus directly, while whiteflies spread it between plants in the field. The disease tends to intensify over successive cycles of propagation from infected material.

• Infected cuttings carry the viruses directly into new plantings
• Whiteflies transmit the viruses between plants in the field
• Repeated propagation from infected plants intensifies the disease
• Neighbouring infected cassava acts as a virus reservoir

Cassava is the primary host of concern. The disease is favoured by whitefly populations, use of cuttings from infected plants, and continuous cassava cultivation that maintains virus reservoirs. Its spread has been associated with the movement of infected planting material and with conditions that support high whitefly numbers.

• High whitefly populations and conditions that favour the vector
• Use of cuttings from infected or unselected plants
• Continuous cassava with nearby infected plants as reservoirs
• Movement of infected planting material into new areas

Management mirrors that of other cassava virus diseases: resistant or tolerant varieties, clean planting material, and removal of infected plants, combined with vigilance because root damage can be hidden. Coordinated clean-seed systems are particularly important given the hidden nature of the disease.

• Plant resistant or tolerant varieties recommended for the local area
• Use clean, virus-tested planting material from healthy mother plants
• Select cuttings only from plants confirmed free of the disease
• Remove and destroy infected plants to reduce virus sources
• Manage whitefly populations and reservoirs where feasible