A Laboratory Assay to Determine Resistance in Butternut to Butternut Canker Disease

Determining disease resistance of large butternut trees in the field is very difficult. In order to assess such trees in the laboratory, four experiments were done with dormant stems of butternut trees (Juglans cinerea) cut in Pennsylvania, enclosed in plastic bags, and shipped by next-day air to Connecticut. Five stems from each tree sampled were inoculated with four strains of the butternut canker fungus (Ophiognomonia clavigignenti-juglandacearum). Inoculated stems were incubated in plastic boxes at 20C in four different experiments, for 12, 13, 14, or 23 days, to determine the best duration. Canker assessments were made by peeling the bark back, and measuring canker diameters. Differences in mean canker growth suggest that this method may be