|Title||Novel insights into the emergence of pathogens: the case of chestnut blight|
|Publication Type||Journal Article|
|chytridiomycosis, cryphonectria-parasitica, diversity, ecology, evolution, exotic pathogen, fungus, genetics, host, invasion biology, keystone species, phytophthora-ramorum, plant pathogen, sudden oak death|
Exotic, invasive pathogens have emerged repeatedly and continue to emerge to threaten the worlds forests. Ecosystem structure and function can be permanently changed when keystone tree species such as the American chestnut (Castanea dentata) are eliminated from a whole range by disease. The fungal ascomycete pathogen Cryphonectria parasitica is responsible for causing chestnut blight. Once the pathogen was introduced into the Eastern US, where chestnuts were predominant, chestnuts were all but eliminated. This pathogen is currently causing extensive damage in Europe. A study in this issue of Molecular Ecology sheds new light on the pattern and process of emergence of this devastating plant pathogen (Dutech 2012). The authors used microsatellite markers to investigate the evolutionary history of C.similar to parasitica populations introduced into North America and Europe. To infer sources of migrants and the migration events, the authors included putative source populations endemic to China and Japan, inferred potentially unsampled populations and conducted a multivariate population genetic and complex ABC analysis. Cryphonectria parasitica emerges as an example of an introduced pathogen with limited genotypic diversity and some admixture in the invaded ranges, yet repeated invasions into different areas of Europe and the United States. This work sheds new light on the emergence of C.similar to parasitica providing compelling evidence that this pathogen emerged by repeated migration and occasional admixture.