Virulence and Isozyme Differences for Establishing Racial Identity in Rusts of Maize. R. R. Bergquist, Plant Pathologist, Pfister Hybrid Corn Company, El Paso, IL 61738. A. J. Pryor, Research Geneticist, Department of Genetics, University of Wisconsin, Madison 53706. Plant Dis. 68:281-283. Accepted for publication 21 September 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-281.

A new race of Puccinia sorghi virulent to maize possessing resistant genes Rp^d, Rp^f, and Rp^Td was found in central Illinois in 1982. This race is designated race 2/Rp^(d-f-Td) to distinguish it from race 1, already known throughout the Corn Belt, that is avirulent on maize with these resistance genes. Resistance gene Rp⁸ conditioned a chlorotic fleck in seedlings to both races. Illinois races 1 and 2 were only distinguished on differential hosts and were indistinguishable in morphology, spore color, or reproductive growth rates on the plant. Illinois strains of races 1 and 2 were identical for two isozyme patterns, whereas a Wisconsin strain of race 1 was differentiated from these by both acid phosphatase and glucose-6-phosphate dehydrogenase banding patterns. P. polysora isozymes were readily distinguished from all P. sorghi biotypes.