American Liberty Elms and Beyond: Going from the Impossible to the Difficult

Abstract

‘American Liberty’ elms are a group of hardy elms from our breeding and selection program which possess an upright vase shape, disease resistance and a vigorous growth habit. These elms constitute a genotypically diverse multiclone variety with similar phenotypes for use in urban areas as a replacement for lost elms killed by Dutch elm disease. Five of the six individuals which comprise the ‘American Liberty’ elm multiclone were derived from controlled pollinations made in 1969 and 1970 between selected Ophiostoma ulmi-resistant parents. One of these (W510) has been patented and named the ‘Independence’ elm. These individuals were selected from more than 530 survivors of inoculated progeny from controlled pollinations (500 series) which involved more than 43 families and over 3,000 individuals. The sixth individual (M-8) was the single survivor of about 1000 inoculated seedlings obtained from Kansas in 1957. Parents of the ‘American Liberty’ elms included superior survivors from our American elm screening program, as well as resistant individuals from the New York and the USDA programs. In total, the parents of ‘American Liberty’ elms are survivors of over 60,000 inoculated American elm seedlings collected from many locations over the northern range of American elm. Selected flowering long-term survivors in the 500 series have been used as parents in further breeding to produce a new (F-2) generation of disease resistant American elms. Certain of these families have yielded nearly 80% resistant individuals following the first field inoculations. Exciting recent research in which the “tetraploid-barrier” of the American elm has been overcome to produce vigorous U. parvifolia x U. americana hybrids retaining paternal hardiness, leaf size and architecture while carrying maternal genes for disease and insect resistance will be reviewed.