VIEW ARTICLE

Ecology and Epidemiology

Epidemiology of Puccinia chondrillina, a Rust Pathogen for the Biological Control of Rush Skeleton Weed in the United States. R. G. Emge, Former research plant pathologist, Agricultural Research, Science and Education Administration, USDA, Plant Disease Research Laboratory, Frederick, MD 21701; J. Stanley Melching(2), and C. H. Kingsolver(3). (2)Research plant pathologist, Agricultural Research, Science and Education Administration, USDA, Plant Disease Research Laboratory, Frederick, MD 21701; (3)Adjunct professor of plant pathology, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 71:839-843. Accepted for publication 13 January 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-839.

Populations of rush skeleton weed (Chondrilla juncea) from California, Oregon, Washington, and Idaho showed differential reactions to infection by the rust pathogen Puccinia chondrillina. Among seven collections of the pathogen, four different virulence patterns were expressed on the host populations. The optimal temperature range for germination of uredospores during a 4-hr incubation on water agar was 11–18 C. The optimal dew period for infection was 16 hr at 10–21 C. In a field plot in the second season following a single artificial inoculation, rusted plants produced 94% fewer seeds, produced seed with 30% less germinability, had a 24% lower 1,000-seed weight, and had 89% less biomass than rustfree plants. Virulent collections of P. chondrillina were increased and supplied to workers in the western United States for release in specific areas for biocontrol of C. juncea. Inoculations resulted in rust initiation, pathogen survival over winter and/or summer in each area, and natural spread of the pathogen to uninoculated areas. This is believed to be the first use of an exotic plant pathogen for weed control in the United States.