Viruses were distinguished as a separate group of plant pathogens in the 1890s, as a consequence of pioneering studies in Russia and the Netherlands (Bos, 2000). They have since received much attention from plant pathologists and more recently from molecular biologists. Nevertheless, the information available on the distribution, prevalence, and importance of plant viruses and the diseases they cause is still incomplete and any attempt to present a global perspective is fraught with difficulties. The main problems arern1. The very wide range of crops and agro-ecologies that must be considered to provide a comprehensive overview of the global situation. Inevitably, the overall research effort has been inadequate in relation to the magnitude of the problems encountered.rn2. The patchy and irregular distribution of plant virologists and facilities in the different regions of the world. In some countries there is a long tradition of plant virology, utilizing well-equipped laboratories and trained personnel. Other countries are in a much less satisfactory situation and the information available is correspondingly limited or almost entirely lacking. Moreover, there are language and cultural barriers to the dissemination of research findings.
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