Evaluation of Elm Clones for Tolerance to Dutch Elm Disease    (View PDF)

A.M. Townsend and L.W. Douglass

Abstract: Rooted cuttings of ten hybrid elm (Ulmus) clones, including one named 'Patriot', and all derived from various crosses of 'Homestead', 'Prospector', 'Urban', and Selection 970, were established along with a randomly selected American elm clones and three disease-tolerant cultivars ('Frontier', 'Homestead', and 'Prospector') in a replicated field plot. When the rooted cuttings were 3 years old, they were inoculated with a mixed spore suspension of Ophiostoma novo-ulmi and O. ulmi, the fungi that cause Dutch elm disease. Analyses of variance and regression showed significant variation among clones in crown dieback, survival, and height growth over a 7-year time period following inoculation. The American elm clone and selection 15-87 (an 'Urban' x 'Prospector' clone) showed the most crown dieback and lowest survival rate and were among the slowest in growth rate, 7 years after inoculation. Selections and cultivars showing the least dieback and highest survival were most hybrids from parentages of 'Urban' x 'Prospector', those from 'Homestead' x 'Prospector', and 'Homestead' x 970; and cultivars 'Patriot', 'Homestead', and 'Prospector'. Many of the same disease-tolerant clones and cultivars also showed the greatest height growth after inoculation. Significant variation in disease symptoms occurred among clones from the 'Urban' x 'Prospector' cross. Results of this study emphasize the importance of selection and testing of specific clones within full-sib families.

Keywords: Disease tolerance; tree breeding and selection; clonal evaluation; Ophiostoma novo-ulmi; Ophiostoma ulmi; Ulmus americana; Ulmus carpinifolia; Ulmus glabra; Ulmus hollandica; Ulmus parvifolia; Ulmus pumila; Ulmus wallichiana; Ulmus wilsoniana.

https://doi.org/10.48044/jauf.2004.022