|Douglass, Larry - UNIVERSITY OF MARYLAND|
Submitted to: Journal Of Arboriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 19, 2003
Publication Date: May 4, 2004
Citation: Townsend, A.M., Douglass. 2004. Evaluation of elm clones for tolerance to dutch elm disease. Journal of Arboriculture. 30(3): 179-184. Interpretive Summary: Rooted cuttings of 14 different elm trees ("clones") were established in a replicated, experimental field plot, to determine their relative tolerance to Dutch elm disease. The 14 clones included ten non-American elm hybrids, including one named 'Patriot,' three disease-tolerant cultivars ('Frontier,' 'Homestead,' and 'Prospector') and one randomly selected American elm. When the rooted cuttings were three years old, they were inoculated with a mixture of the two fungi which cause Dutch elm disease. A statistical analysis showed significant differences among the clones in crown dieback, survival, and height growth over a 7-year period. Selections and cultivars showing the least crown dieback and highest survival were hybrids of 'Urban' x 'Prospector,' 'Homestead' x 'Prospector,' 'Homestead' x selection 970, and cultivars 'Patriot,' 'Homestead,' and 'Prospector.' Differences in degree of disease tolerance occurred among clones derived from the cross, 'Urban' x 'Prospector.' These results of relative disease tolerance indicate the importance of intensively testing specific clones from crosses of the same parentage.
Technical Abstract: Rooted cuttings of ten hybrid elm 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 clone and three disease-tolerant cultivars ('Frontier,' 'Homestead,' and 'Prospector') in a replicated field plot. When rooted cuttings were three years old, they were inoculated with a mixed spore suspension of Ophiostoma novo-ulmi and Ophiostoma ulmi, the fungi causing 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, seven years after inoculation. Selections and cultivars showing the least dieback and highest survival were many hybrids from parentages of 'Urban' x 'Prospector,' '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.