Human-mediated migration of plants, their pathogens and parasites

The adoption of agriculture in several parts of the world during the early Neolithic period led to a fundamental change in human migration. By introducing newly domesticated crops into new environments, pathogens and parasites were also inadvertently transferred from their regions of origin and underwent a considerable population growth. In the newly settled regions, some pests of indigenous plants adapted to new crops by host switching. This review is limited to three basic migration events and mainly to agricultural crops of the temperate zone: (1) the migration of the first farmers from SE Asia to Europe, (2) European expansion from the 16th century onward, (3) modern globalization since the 20th century. Molecular analyses offer the opportunity to study the evolutionary history of pest populations, their origin and dynamics and their spread around the world. Cereals’ rusts and powdery mildew, storage insects were the first to spread with wheat species, barley, and pulses from the Levant across Eurasia. The Columbian exchange of crops to and from the Americas brought entirely new pests to Europe while old world pathogens spread to the Americas and subsequently to all other regions colonized by Europeans. Modern globalization further facilitated the spread of pathogens and insects worldwide, as previously inconceivable amounts of agricultural products, business travelers, and maybe tourists have elevated global accessibility. This is illustrated by case studies based on fungi and insects. In the near future, pests will have colonized all crops in all countries where they can exist according to their agro-climatic requirements.