VIEW ARTICLE

Resistance

Resistance of Hybrid Elm Progenies to Ceratocystis ulmi. A. M. Townsend, Research Geneticist, Nursery Crops Research Laboratory, Agricultural Research Service, U. S. Department of Agriculture, Delaware, OH 43015; L. R. Schreiber, Research Plant Pathologist, Nursery Crops Research Laboratory, Agricultural Research Service, U. S. Department of Agriculture, Delaware, OH 43015. Phytopathology 66:1107-1110. Accepted for publication 22 March 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1107.

Five clones of Ulmus from the Netherlands, and with resistance to Ceratocystis ulmi, when hybridized as male parents with Ulmus pumila varied in their ability to transmit genes for Dutch elm disease resistance and growth rate. Significant differences in disease symptoms among the progenies occurred 15 and 56 weeks but not 4 weeks after inoculation. The progeny from one Dutch clone, N248 (U. wallichiana × U. carpinifolia), was more susceptible than were progenies from other clones. Ulmus rubra × U. pumila as a female parent transmitted a slower growth rate and less disease resistance to its progeny than did U. pumila. Date of inoculation, interaction between inoculation date and progeny, and site factors rarely influenced symptom expression. One Ceratocystis ulmi isolate from Tennessee and labeled earlier as “nonaggressive” similarly caused less disease than did six other “aggressive” isolates when tested on U. pumila × N260 (U. pumila × U. hollandica).