Virus Diseases of Tropical Crops

Abstract

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. Accurate pathogen diagnosis is the key to managing diseases. The main virus and viroid diseases of 18 different crops are listed and pathosystem descriptors provided for each based on the mode of spread, which in turn informs the different management strategies. The Tenth Report of the International Committee on Taxonomy of Viruses, which is available online at https://talk.ictvonline.org/ictv‐reports/ictv_online_report/ , 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 postulates 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 databases. Epidemics are driven by virus, vector, host, environment, time and human activity. The 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 downregulating one or more components of the relevant pathosystem.