Emergence, spread and strategies for controlling the pandemic of cassava mosaic virus disease in east and central Africa

Abstract

During the 1990s, an epidemic of an unusually severe form of cassava mosaic virus disease (CMD) has expanded to cover virtually all of Uganda, and substantial areas in the neighbouring countries of Kenya, Tanzania, Sudan and the Democratic Republic of Congo. Losses in the generally sensitive local cassava cultivars have been so great that a common farmer response to the problem has been the temporary abandonment of cassava cultivation. As a consequence, the CMD `pandemic’ has had a significant destabilising effect on food security in East Africa. In attempting to combat the problem, vigorous efforts have been made to identify, multiply and disseminate resistant cassava germplasm. This has included cultivars obtained from the breeding programme of the International Institute of Tropical Agriculture (IITA), based in Nigeria, as well as local selections derived from IITA parent stock. Whilst considerable success has been realised in controlling the pandemic in Uganda, addressing the problem at the regional level remains a major challenge. This article reviews progress made in recent years, both in understanding the cause and mechanisms behind the pandemic's expansion, and in developing strategies to control it. Particular attention is drawn to the likely threat the pandemic poses to cassava production in the countries of central Africa, most notably the Democratic Republic of Congo, where insecurity currently impedes an assessment of the problem and the ready implementation of control measures. Scientists and other stakeholders with an interest in CMD management are therefore urged to explore innovative mechanisms that will allow them to develop a more comprehensive approach to CMD control in the region.