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43

Characterizing resistance of soybean accessions to soybean rust (Phakopsora pachyrhizi Syd.)

Presenter: T. A. Pham

All authors and affiliations: T. A. PHAM (1), N. T. Binh (2), T. D. Vuong (3), M. R. Miles (5), G. L. Hartman (1,5), L. D. Tran (4), R. D. Frederick (6), H. Nguyen (3), and T. VanToai (7). (1) Department of Crop Sciences, University of Illinois, Urbana, IL 61801; (2) Plant Protection Research Institute, Hanoi, Vietnam; (3) NCSB, University of Missouri, Columbia, MO 65211; (4) Foods Crop Research Institute (FCRI), Hanoi, Vietnam; (5) USDA-ARS and Department of Crop Sciences, University of Illinois, Urbana, IL 61801; (6) USDA-ARS Foreign Disease-Weed Science Research Unit, Fort Detrick, MD 21702-5023; and (7) USDA-ARS-SDRU, Columbus, OH 43210

Soybean rust (Phakopsora pachyrhizi Sydow) was introduced into the continental United States in November 2004. The utilization of resistant cultivars may be the most sustainable means of disease control. Resistance has been identified but has not been durable. As part of the effort to identify new sources of resistance, experiments were conducted at the Plant Protection Research Institute (PPRI) and the USDA-ARS Foreign Disease-Weed Science Research Unit (FDWSRU) BSL-3 Plant Pathogen Containment Facility in Fort Detrick, MD. Fifty-seven soybean accessions, previously identified as resistant, were screened in the field at VASI during January through May 2005. Based upon the first evaluation, 39 of the accessions were subsequently evaluated in two consecutive seasons. Three accessions, PI 437323, PI 398998, and PI 459025B, with resistant reddish brown lesions and low sporulation levels were identified. A fourth accession, PI 549017, with a low number of tan lesions was also identified. Two accessions, PI 437323 and PI 398998, along with four accessions from Paraguay and nine cultivars from Vietnam that have been identified as containing rust resistance, accessions containing the known single rust resistance genes (Rpp1-Rpp4), and the susceptible cultivar Williams 82 were inoculated in seedling assays at the FDWSRU with each of 10 soybean rust isolates. All accessions, but one, had a race-specific response to one or more of the rust isolates. The exception was PI 459025B (Rpp4), which was resistant to all rust isolates. The reactions of the accessions selected for resistance in this study differed from that of the four accessions with known genes, indicating that they may be potential sources of new resistance genes.

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