Adaptive differences between Phytophthora ramorum isolates from Europe and North America: evidence for separate subspecies?

The comparative risk to trees posed by European (E.U.) versus North American (U.S.) isolates of Phytophthora ramorum, the possible risk posed by genetic recombination between them, and whether European versus North American isolates represented discrete sub-populations was investigated. Population samples of E.U. and U.S. isolates were compared for growth rate across different environments (gene x environment tests), phenotypic stability, host range, pathogenic aggressiveness and sexual behaviour.