Evolution and Management of the Irish Potato Famine Pathogen Phytophthora Infestans in Canada and the United States

Late blight, caused by Phytophthora infestans (Mont.) de Bary, is the most historically significant and economically destructive disease of potatoes (Solanum tuberosum L.). In addition to potato, P. infestans can also infect tomato and some other members of the Solanaceae, and this has contributed to the recent late blight epidemic in Canada and the United States. Propagation of P. infestans in Canada and the United States has been mainly through asexual reproduction and this has led to the development of several dominant clonal lineages. Various P. infestans markers have been developed that are invaluable in monitoring the evolution and movement of these P. infestans genotypes. Population diversity and disease incidence has increased through the development of systemic fungicide insensitivity and the transcontinental shipment of the pathogen on late blight infected potato tubers and tomato plantlets. Introduction of the P. infestans A2 mating type to several regions of Canada and the United States has also increased the opportunity for sexual reproduction and recombination, potentially contributing to greater P. infestans genetic diversity and pathogenicity. Advances in P. infestans molecular analysis have revealed a complex pathogen with a genome capable of evolving relatively quickly. Management of late blight will therefore require new, multifaceted strategies which include monitoring pathogen evolution and implementing sustainable production practices.