ABSTRACT
Diseases affecting cassava James Legg, International Institute of Tropical Agriculture (IITA), Tanzania; and Elizabeth Alvarez, International Center for Tropical Agriculture (CIAT), Colombia
1 Introduction
2 Viral cassava diseases in Africa
3 Viral cassava diseases in Latin America and Asia
4 Bacterial blight, phytoplasmas and frogskin disease
5 Cassava fungal diseases: foliar
6 Cassava fungal diseases: root rots
7 Summary
8 Future trends in research
9 Where to look for further information
10 References
Cassava is primarily a vegetatively propagated crop, and consequently, it is vulnerable to infection by pathogens that pass from one cropping cycle to the next through the planting material, which is typically stem cuttings. Diseases have been some of the most important constraints to cassava production since the early days of published crop disease reports. Notably, the cassava mosaic-causing viruses that remain a major constraint today were first reported as far back as the end of the nineteenth century (Warburg, 1894). One of the earliest reports of bacterial disease from Latin America is also more than a century old (Berthet and Bondar, 1915). All the major plant disease-causing agents – bacteria, fungi, viruses and phytoplasmas – cause economically important damage to cassava through large parts of the regions, countries and continents within which the crop is grown. However, there are important differences in patterns of distribution. Although this point will be discussed in detail later in this chapter, it is important to highlight here that these differences mean that there continue to be significant risks of the spread of pathogens with a limited current distribution to parts of the world in which they do not currently occur. Although many of the diseases of cassava are most readily spread through vegetative propagules, several have important interactions with insect vectors. A key feature of this interaction is that changes in abundance levels or patterns of distribution of vectors can have significant consequences for the transmission and geographical spread of the
pathogens that they vector. Since insects can be particularly sensitive to abiotic factors, such as temperature, this also means that anticipated climate change will have a significant impact on transmitted pathogens.
