Oral: Pathogen Ecology
Model for the geographic origin and spread of the globally distributed pathogen Phytophthora palmivora
J. Wang (1), E. Goss (1), M. Coffey (1) (1) University of Florida, U.S.A.
The genetic structure and diversity of plant pathogens are shaped by their evolutionary history, including coevolutionary interactions with hosts, geographic spread, and long-distance migration events, often mediated by humans. In turn, diversity and dispersal of present populations impact the risk of disease epidemics and strategies for controlling disease. Phytophthora palmivora is a globally distributed oomycete that infects a broad range of cash crops and fruit trees in the tropics and subtropics, including cocoa and palms. The center of diversity of P. palmivora is in Southeast Asia, but it is an important and widespread pathogen in South America. Our multilocus sequence analysis showed that the centers of origin of the pathogen are located in the Philippines and Indonesia. We then tested alternative models for the regional and global movement of P. palmivora. We found genetic variation consistent with historical movement among Pacific Islands, likely associated with coconut. We also found evidence of a bridgehead effect in South America, in which the colonization of South America and host shift to cocoa led to further global dispersal, including gene flow back to Southeast Asia. We propose that the extensive genetic diversity in P. palmivora in Southeast Asia is the result of a complex history, including long-term co-evolution with native hosts, geographic isolation with migration, and re-introduction of genotypes from South America.