Environmental Effects on the Development of Brown Stem Rot in Soybean. R. S. Waller, Former Graduate Research Assistant, Department of Agronomy, USDA-ARS, University of Illinois, Urbana 61801. C. D. Nickell, and L. E. Gray. Professor, Department of Agronomy, and Professor and Plant Pathologist, Department of Plant Pathology, USDA-ARS, University of Illinois, Urbana 61801. Plant Dis. 76:454-457. Accepted for publication 12 December 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0454.

Brown stem rot of soybean (Glycine max), caused by Phialophora gregata, can cause significant yield reductions under favorable environmental conditions. Leaf symptoms may not always be present in the field; therefore, field evaluation must rely on stem symptoms. Eleven genotypes from maturity groups I, II, and III were planted in hill plots (three plants per hill) in two environments with different fertility and crop rotations for two years, 1988 and 1989, with and without inoculation with P. gregata. All genotypes showed greater development of brown stem rot stem symptoms under low fertility and in inoculated plots. Significant increases in stem symptoms were observed for three of six susceptible genotypes in the two environments. Field evaluations can be highly variable from year to year and within years. Inoculation caused a significant increase in disease development for all susceptible genotypes. Field evaluation and selection for brown stem rot resistance may be more efficient in areas with low fertility and high levels of inoculum of P. gregata.