Tracing the role of human civilization in the globalization of plant pathogens

Co-evolution between plants and parasites, including herbivores and pathogens, has arguably generated much of Earth’s biological diversity. Within an ecosystem, coevolution of plants and pathogens is a stepwise reciprocal evolutionary interaction: epidemics result in intense selection pressures on both host and pathogen populations, ultimately allowing long-term persistence and ecosystem stability. Historically, plants, and pathogens evolved in unique regional assemblages, largely isolated from other assemblages by geographical barriers. When barriers are broken, non-indigenous pathogenic organisms are introduced into new environments, potentially finding suitable hosts lacking resistance genes and environments favouring pathogenic behavior; this process may result in epidemics of newly emerging diseases. Biological invasions are tightly linked to human activities and have been a constant feature throughout human history. Several pathways enable pathogens to enter new environments, the great majority being human mediated.