Ecology and Epidemiology of Virus and Viroid Diseases of Tropical Crops

Abstract

Epidemiology deals with the occurrence of diseases in plant populations over time and space. A plant virus epidemic results from interactions between virus, host plant, vectors and environmental conditions. Every epidemic can be considered to be a unique pathosystem in which each of the components contributes to the epidemics or outbreak of the disease. Epidemiology is not a static process but a dynamic course that varies with a change in the ecology, host, vector and virus systems. Primarily the effect of environmental conditions on virus disease development becomes apparent when influence of disease development is considered in relation to temperature, rainfall, humidity, vector population and so on. The infected sources like weeds and wild hosts, infected seeds and/or adjacent infected crops can also play a major role for high virus incidence. Similarly, crop growing seasons, cropping practices and host genetic vulnerability are also important factors for epidemics to occur. The progress of disease varies with respect to virus, vector, location, and weather conditions. The movement of the vector within a crop field is related to prevailing meteorological conditions. Genetic RNA or DNA recombination is a major factor responsible for the emergence of new viral strains of species. The epidemiology of plant virus diseases is concerned to the cyclical development of diseases within the plant populations in time and space. Aspects like disease gradients, progress curves, spatial dynamics and meta-populations, systems analysis and simulation models are also discussed in detail. The factors that deal with how and why a virus spreads by vectors in an ecosystem are fundamental to the choice and improvement of control measures in agriculture. The authors herein have focused on the latest information pertaining to ecology and epidemiology of major virus and virus-like diseases in the tropics.