VARIABILITY IN AGGRESSIVENESS, RECOVERY, AND CULTURAL CHARACTERISTICS OF ISOLATES OF CERATOCYSTIS-ULMI

Seedlings of several elm species were inoculated with isolates of C. ulmi from various geographic areas in the USA. The isolates caused different amounts of foliar and vascular symptoms regardless of seedling species, age or environment. The more aggressive isolates were recovered from Ulmus pumila more frequently than the less aggressive ones, but all were recovered with about equal frequency from U. americana. With some exceptions, the more aggressive isolates grew more rapidly on agar media, were intermediate in mycelial habit between appressed and fluffy, and produced more coremia on wood of both U. americana and U. pumila.