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13

Alternative hosts to Phakopsora pachyrhizi, the causal agent of soybean rust

Presenter: T. N. Lynch

All authors and affiliations: T. N. LYNCH (1), M. R. Miles (2), R. D. Frederick (3), M. R. Bonde (3), and G. L. Hartman (1,2). (1) Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801; (2) USDA-ARS, National Soybean Research Center, Urbana, IL 61801; and (3) USDA-ARS, Foreign Disease-Weed Science Research Unit, Fort Detrick, MD 21702

Phakopsora pachyrhizi Syd. & P. Syd. is known to have a broad host range. Little is known about whether the legumes in the United States could be hosts of P. pachyrhizi. In this study, 176 species representing 57 genera of legumes, the majority of which are either native or naturalized to soybean-growing areas of the United States, were tested at the USDA-ARS Foreign Disease-Weed Science Research Unit (FDWSRU) Plant Pathogen Containment Facility in Fort Detrick, MD. A total of 264 accessions (between one and three accessions per species) was inoculated with a mixture of four P. pachyrhizi isolates collected in 2001 from Brazil, Paraguay, Thailand, and Zimbabwe. Plants were rated 14 days later, reinoculated, and rated again 14 days after reinoculation. Severity and sporulation data were taken on both dates using a 15 scale (1 = no visible symptoms; 5 = fully susceptible). There were 55 new host species among 25 genera that were observed to have symptoms. Fourteen of these genera have not been previously reported. These alternative hosts could serve as additional inoculum sources and provide additional overwintering sites for the pathogen.

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