Xylem characteristics in Ulmus americana cultivars and their potential use as a preliminary screening method for Dutch elm disease resistance.

Traditional screening of American elm (Ulmus americana) for resistance to Dutch elm disease (DED) often requires many years between initial propagation of trees and inoculation of older trees in the field. Previously published studies have found an association between smaller vessel diameters and increased resistance to DED, but further validation was needed to determine whether it could provide a rapid screening method to identify candidate trees for further testing. This investigation examined xylem characteristics in main stems of three‐year‐old trees for five cultivars and two wild‐type seedling populations of U. americana with varying levels of resistance to DED. Cultivars with low disease severity ratings tended to have smaller vessel diameters and higher vessel densities than cultivars with high disease severity ratings. Xylem characteristics were also assessed in branches and main stems of larger plant material. Data suggest that the use of main stems is preferential to branches when evaluating large trees, as main stems provided more resolution in differentiating between the genotypes. Results from this study indicate that there is potential for the use of xylem characteristics, such as vessel diameter and vessel density, for selecting trees with putative resistance. However, caution should be used due to the potential effects of the environment, such as the effect of water availability and its impacts on xylem development. [ABSTRACT FROM AUTHOR]