Virulence in Eastern North American Populations of Puccinia sorghi to Rp Resistance Genes in Corn. J. V. Groth, Department of Plant Pathology, University of Minnesota, St. Paul 55108. J. K. Pataky, and G. R. Gingera. Department of Plant Pathology, University of Illinois, Urbana 61801; and Department of Horticultural Science, University of Minnesota, St. Paul 55108. Plant Dis. 76:1140-1144. Accepted for publication 16 July 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1140.

The effectiveness of 24 alleles from four Rp loci that condition race-specific resistance to common rust (Puccinia sorghi) in corn (Zea mays) was evaluated in field trials from 1987 to 1991 at many locations in eastern United States and one in central Mexico. In natural and/or inoculated epidemics, near-isogenic lines containing each gene were scored for the presence of susceptible-type uredinia. Only two genes (Rp₁^d and Rp₃^c) were totally effective, with no large uredinia observed in any trial. Also, an unnamed gene from M165sel was totally effective during the 3 yr it was tested in St. Paul, Minnesota. Four other genes—Rp₁^e, Rp₁^f, Rp₁^g, and Rp₁^k—showed no more than a trace of rust in a few trials. Lines containing any of the other 17 genes had light to heavy rust levels in most trials in which they were tested.