Progress in the Development of Disease-Resistant Elms

Abstract

An extensive program designed to genetically enhance elms is being carried out by the U. S. National Arboretum, USDA-ARS, Washington, DC. The emphasis is on breeding for greater resistance to the fungus, Ophiostoma ulmi (Buism.) C. Nannf., that causes Dutch elm disease. The cultivars released to date are diploid in chromosome number and are ‘Urban’, ‘Dynasty’, ‘Homestead’, ‘Pioneer’, ‘Frontier’, ‘Prospector’, ‘Pathfinder’, and ‘Ohio’. Advanced generation crosses have been made in order to combine tolerance to Dutch elm disease with resistance to the elm leaf beetle and have resulted in over 700 seedlings, three of which have been sent out for nursery evaluation because of their superior pest resistance. With American elm, more than 20 promising clones are being compared for superiority in disease resistance in replicated field trials. Future emphasis will be on the evaluation and release of exceptional American elms and advanced generation hybrid clones.