Date: 10 Nov 2009

Globalisation and the Threat to Biosecurity

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Abstract

Globalisation has led to a dramatic increase in trade and travel and exotic species are now being exchanged, either accidentally or deliberately, at unprecedented rates between geographically isolated regions, countries and continents. Thus, the natural barriers that once separated the world’s floras and faunas are no longer effective and invasive alien species pose potent and burgeoning threats to both natural and agricultural ecosystems. Due to a combination of luck, in the early days, and judicious selection or quarantine, in later times, man successfully separated many of the coevolved natural enemies (pests and pathogens) from his crop plants, increasing their fitness to such an extent that most of the major crops were concentrated outside their centres of origin, free from natural–enemy pressures. However, progressively accelerating globalisation over the past 150 years has meant that coevolved natural enemies have been catching up with their plant hosts, often with disastrous socio-economic consequences. We review the problem of emerging infectious diseases (EIDs) of crop plants, using past and present examples, and the main factors driving them. Principal amongst these drivers is pathogen pollution involving the anthropogenic movement of disease-causing organisms across evolutionary and geophysical boundaries. In addition, case studies of EIDs of staple food and commodity crops are presented, with particular reference to witches’ broom disease of cocoa as this host-pathogen association embraces all aspects of globalisation and biosecurity. Finally, we identify weaknesses in global phytosanitary protocols, especially for the exchange of germplasm, and discuss measures which could be taken to improve them.