Abstract
Disease emergence is a growing threat to agricultural productivity worldwide, yet plant pathology is primarily focused on populations sampled from cultivated crops. There is increasing evidence environmental reservoirs contribute to disease emergence however. While the arms race model has considerable explanatory power for tightly coevolving hosts and pathogens in agricultural contexts, it may be unsuitable for describing the dynamics of pathogens infecting natural host populations. Greater spatial, environmental and genetic heterogeneity and variable disease prevalence and severity may result in the long-term maintenance of genetic variation in both host resistance and pathogen virulence genes. The maintenance of polymorphism in wild pathogen populations represents a disease reservoir from which virulent genotypes may emerge to cause epidemics in agricultural environments. The emergence of Pseudomonas syringae pv. actinidiae (Psa) over the last three decades - concomitant with the domestication of its kiwifruit (Actinidia spp.) host - offers a unique opportunity to understand the relationship between wild and cultivated populations of both plants and microbes and the ecological and evolutionary factors driving disease emergence and establishment in agricultural settings.
