Effects of Powdery Mildew Alleles Rmd-c, Rmd, and rmd on Yield and Other Characteristics in Soybean. D. G. LOHNES, Department of Agronomy, National Soybean Research Laboratory, University of Illinois, 1101 W. Peabody, Urbana 61801. C. D. NICKELL, Department of Agronomy, National Soybean Research Laboratory, University of Illinois, 1101 W. Peabody, Urbana 61801. Plant Dis. 78: 299-301. Accepted for publication 3 December 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0299.

This study was conducted to determine whether soybean (Glycine max) yield differs among soybeans nearly isogenic except for reaction to Microsphaera diffusa under a powdery mildew epidemic. Eleven isolines of cvs. Clark and Williams containing the powdery mildew reaction alleles Rmd-c (resistant), Rmd (adult-plant resistant), and rmd (susceptible) were evaluated for yield, lodging, height, seed quality, seed mottling, seed weight, and resistance to powdery mildew and brown stem rot. Isolines containing the resistance alleles Rmd-c and Rmd yielded 18% more than isolines containing rmd when stressed by a powdery mildew epidemic. The Rmd-c isolines yielded 7% more than the Rmd isolines. This difference suggests that it would be advantageous to use Rmd-c as a marker for Rps2 in a soybean breeding program. There also appears to be a potential linkage between the Rmd locus and a gene providing resistance to brown stem rot.