Reactions of Maize Lines Carrying Rp Resistance Genes to Isolates of the Common Rust Pathogen, Puccinia sorghi. S. H. Hulbert, Assistant Professor, Department of Plant Pathology, Kansas State University, Manhattan 66506-5502. P. C. Lyons, and J. L. Bennetzen. Postdoctoral Associate, and Professor, Department of Biological Sciences, Purdue University, West Lafayette, IN 47907. Plant Dis. 75:1130-1133. Accepted for publication 13 May 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1130.

Isolates of the common rust fungus, Puccinia sorghi, were collected from North America, Hawaii, and Africa, and their specific virulence phenotypes were tested using a collection of maize lines carrying different resistance genes. Although all of the isolates collected in 1988 had identical specific virulence phenotypes, the pathotypes collected in 1989 were phenotypically diverse. Maize lines, the resistances of which could not be differentiated by a previous collection of rust isolates of this fungus, usually could not be differentiated by these isolates. One exception was the cultivar Golden King, which was differentiated from other lines carrying Rp1^A by the presence of an additional, previously uncharacterized, resistance factor. This resistance segregated as a single dominant gene independent of the Rp1 locus.