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Evaluating Soybean Germ Plasm for Brown Stem Rot Resistance. Randall L. Nelson, Research Geneticist, USDA-ARS, and Assistant Professor, Department of Agronomy, University of Illinois, Urbana 61801. C. D. Nickell, J. H. Orf, H. Tachibana, E. T. Gritton, C. R. Grau, and B. W. Kennedy. Professor of Plant Breeding, Department of Agronomy, University of Illinois, Urbana 61801; Associate Professor, Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul 55108; Research Plant Pathologist, USDA-ARS, Department of Plant Pathology, Seed, and Weed Sciences, Iowa State University, Ames 50011; Professor, Department of Agronomy, Associate Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706; and Professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Plant Dis. 73:110-114. Accepted for publication 23 August 1988. 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, 1989. DOI: 10.1094/PD-73-0110.

Over 3,400 accessions from the USDA Soybean Germplasm Collection in maturity groups 000 to IV were evaluated between 1981 and 1984 for resistance to brown stem rot (BSR) caused by Phialophora gregata. Lines were evaluated in naturally infested fields at latitudes to which they were adapted. In 1985 and 1986, 13 early maturity, and 25 late maturity, putatively resistant lines were evaluated in replicated tests. The early maturity material was tested at Rosemount, MN, Hancock, WI, and Ames, IA. The late maturity material was tested at Ames, IA, and Urbana, IL. Each line also was evaluated in the greenhouse at Urbana, IL. Ratings at Hancock, WI, and in the greenhouse were based on leaf symptoms. All other ratings were based on stem symptoms. No lines were immune to BSR. In the early maturity test, no lines were as resistant as the resistant standards at all locations, but several lines were highly resistant at two or more locations. In the late maturity test, three lines (PI 424.285A, PI 424.353, and PI 424.611A) were resistant in all tests, but were not superior to previously identified sources. Many lines had inconsistent responses across environments and reasons for those interactions are discussed.