Early Screening of Elms for Resistance to Ceratocystis ulmi. Carrie E. Green, Department of Forestry, University of Wisconsin, Madison 53706. Raymond P. Guries, Department of Forestry, and Eugene B. Smalley, Department of Plant Pathology, University of Wisconsin, Madison 53706. Plant Dis. 69:60-63. Accepted for publication 25 June 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-60.

The repeatability of an early screening technique to evaluate resistance to Ceratocystis ulmi, the cause of Dutch elm disease, was tested with selected elm clones in their first year of growth. In controlled-environment chambers, significant differences among elm clones, incubation temperatures, and fungus strains were detected. American and English elms and the cultivar Belgica showed low levels of resistance; the cultivars Groeneveld, Dodoens, Lobel, and Plantyn showed moderate resistance; and the cultivars Regal, Christine Buisman, and Sapporo Autumn Gold showed high resistance. Aggressive and nonaggressive strains of C. ulmi were clearly differentiated by the range of clones and incubation temperatures employed.