Univ. of Calif.-Berkeley plant pathologists say genetic analysis of Phytophthora ramorum isolates indicate that the nursery industry may be responsible for unknowingly spreading the pathogen to California forests. Since the 1990s, the funguslike pathogen has killed hundreds of thousands of oaks and tanoaks along the Pacific Coast. It appears that a single strain of P. ramorum was initially introduced in U.S. forests, said Kelly Ivors, former U.C.-Berkeley post-doctoral student now with N.C. State Univ. Different strains exist in the European nursery trade, and at least 3 strains can be found in U.S. nurseries, Ivors said. It's unknown how U.S. and European nurseries were originally infected, but the leading theory is imported host plant material, Ivors said. Experts' best guess is the pathogen originated in the Indo-Malaysian region of Asia, but this has not been confirmed.