Migration from northern Mexico as the probable cause of recent genetic changes in populations of Phytophthora infestans in the United States and Canada.

Isolates of Phytophthora infestans from five U.S. states (California, Florida, New York, Washington, and Wisconsin) and one Canadian province (British Columbia) collected between October 1987 and October 1991 were analyzed for mating type and for genetic variation at two allozyme loci. A subset of these 155 isolates, which included all of the allozyme genotypes plus 26 isolates from our culture collection that had been collected in the United States and Canada during 1979-1987, were analyzed for DNA fingerprint variation. These analyses revealed 18 genotypes among the 120 isolates that were analyzed for all markers [...]