Virus Diseases of Tropical Crops


Virus diseases are serious constraints to the productivity and profitability of a wide range of tropical crops. Identification of the causal viruses and understanding their epidemiology is the key to estimating the incidence and economic impact of the diseases they cause, and to devising virus management strategies. Epidemics result from interactions between virus, host plant, vector and environmental factors, and every epidemic can be considered to be a unique pathosystem in which each of the components contributes to the epidemic, and in which none are limiting. Pathogen diagnosis is the key to managing diseases, and we list 18 crops, their main virus/viroid diseases and pathosystem descriptors for each. Six types of pathosystem are described on the basis of the mode of spread, and the different management strategies applicable to each are discussed. The Ninth Report of the International Committee on Taxonomy of Viruses (2012) is an essential reference for virologists working with tropical crops.

Key Concepts:

  • Identification of viruses or viroids is the key to managing the diseases they cause.

  • Koch's rules are applied to establish causal associations between viruses/viroids and disease.

  • Viruses/viroids are identified by their biological, morphological and genetic properties using classical and molecular methods.

  • The universal database for viruses/viroids published by the International Committee on Taxonomy of Viruses is the resource for classification.

  • Rapid diagnostic methods rely on nucleotide sequence comparisons with publicly available data bases.

  • Epidemics are driven by virus, vector, host, environment, time and human activity.

  • Vector–virus interaction is the main determinant of the rate, range, timing and pattern of disease spread.

  • Viruses/viroids of tropical plants have unique pathosystems.

  • A full description of a pathosystem is required to sustainably manage virus epidemics.

  • Management of epidemics can be achieved by destabilising or down‐regulating one or more components of the relevant pathosystem.

Keywords: Geminiviridae; Potyviridae; Tospovirus; Caulimoviridae; Nanoviridae; Pospiviroidae; Sobemovirus; taxonomy; pathosystem; management

Figure 1.

Global distribution of the tropical wet, and tropical wet and dry zones. Reproduced from

Figure 2.

A general plan showing the infection cycle of plant viruses (Randles, ). Plant viruses follow one or more of the pathways shown when they spread between plants. A virus may be retained within a crop cultivar either by vegetative propagation (pathosystem 1; see Figure ) or by pollen or seed transmission (pathosystem 2); it may spread by mechanical transmission (pathosystem 3), or it may be spread by a vector. The association of the virus with the vector may be non or semi‐persistent (pathosystem 4); it may be persistent and circulative (pathosystem 5), or the virus may replicate in the vector, perhaps infecting its progeny transovarially or it may survive in resting spores of a fungal vector (pathosystem 6). Reproduced from Randles, . Copyright by Australasian Plant Pathology Society Inc.

Figure 3.

The definitions of pathosystems 1–6 showing their application as descriptors of the modes of spread of plant viruses between infector A and infectee B. The circle indicates that the virus remains either within ramets from a clone (pathosystem 1) or remains within a gene pool determined by the ability of the virus/viroid to invade gametophytes (pathosytem 2). Pathosystems 3–6 show various methods of transfer between susceptible plants.



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Further Reading

Fargette D, Konate G, Fauquet C et al. (2006) Molecular ecology and emergence of tropical plant viruses. Annual Review of Phytopathology 44: 235–260.

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Roossinck MJ (ed.) (2008) Plant Virus Evolution. 223 pp. Berlin: Springer.

Thresh JM (2006) Control of tropical plant virus diseases. Advances in Virus Research 67: 245–295.

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Geering, Andrew D W, and Randles, John W(Sep 2012) Virus Diseases of Tropical Crops. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000767.pub2]