A variety of methods have been used by different research groups to "challenge" inoculate American elms (Ulmus americana) with the purpose of determining whether some clones may be resistant to the Dutch elm disease fungus. The methods used by seven research groups are described, along with observations on complications and benefits associated with each. The response of test trees to challenge is affected by many factors, including the age of parent material, size/maturity of test material, vigor of the plant being inoculated, portion of the plant inoculated, season/time of year, source of inoculum, amount of inoculum, and method of delivery. The testing goal must be kept in mind when choosing methods, and the details of what methods were used must be described when reporting results. Inclusion of susceptible and resistant controls is critically important, as it allows calibration of response between different studies.
This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.