Relative Virulence of Melampsora euphorbiae from Central Europe Toward North American and European Spurges. W. L. Bruckart, Research Plant Pathologist, USDA Foreign Disease-Weed Science Research Unit, Ft. Detrick, Bldg. 1301, Frederick, MD 21701. S. K. Turner, Research Associate, and E. M. Sutker, Research Associate, USDA Foreign Disease-Weed Science Research Unit, Ft. Detrick, Bldg. 1301, Frederick, MD 21701; and R. Vonmoos, Graduate Student, L. Sedlar, Research Associate, and G. Defago, Professor, Institute für Phytomedizin, ETH-Zentrum, CH-2800, Zürich, Switzerland. Plant Dis. 70:847-850. Accepted for publication 3 April 1986. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1986. DOI: 10.1094/PD-70-847.

Isolates of Melampsora euphorbiae collected in Austria, Hungary, Italy, and Switzerland were evaluated for virulence and specificity toward leafy and cypress spurges. Host specificity studies conducted for five of these isolates revealed that each isolate was most virulent on the collection of leafy or cypress spurge from which it came, and one isolate was restricted to its original collection of leafy spurge. Two of the isolates infected both leafy and cypress spurge, and though each was highly virulent toward the species of origin, it was only weakly virulent on the other. Three of the five isolates also infected a few North American collections of leafy or cypress spurge, but disease severity was very low in each instance. Reasons for desirability to collect M. euphorbiae from other geographical locations are given.

Keyword(s): biological weed control, Euphorbia sp.