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Disease Note.

Previously Undescribed Pathotype of Bipolaris zeicola on Corn. J. L. Dodd, President, Professional Seed Research, Inc., Sugar Grove, IL 60554. A. L. Hooker, Scientific Director, Plant Molecular Biology Center, Northern Illinois University, DeKalb, IL 60115. Plant Dis. 74:530. Accepted for publication 13 March 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0530D.

A previously undescribed pathotype of Bipolaris zeicola (Stout) Shoemaker (Helminthosporium carbonum Ullstrup) was associated with damage to corn inbreds in a breeding nursery and seed production fields io northern Illinois in August-September 1989. Susceptible inbreds had early and sudden leaf death, becoming reddish brown, as if killed by a toxin, lesions within the dead tissue were oval to circular and 5- 10 mm in diameter, often containing concentric circles. Most susceptibility was expressed in inbreds with B73 background. A few unrelated inbreds were also susceptible. Inbreds with predominantly B14, B37, 0h43, or Mo17 heritage generally had much less severe symptoms. The pathogen was also associated with scattered lesions in hybrid fields in five northern Illinois counties. Lesions on some hybrid geootypes were smaller, nearly cream colored, and without concentric circles. B. zeicola was consistently isolated from both types of lesions. Inoculation trials in the greenhouse showed that isolates from both lesion types resulted in lesions with concentric rings on some genotypes. Although the pathogen was morphologically indistinguishable from isolates of races I1, 2, and 3 of B. zeicola, lesion symptomatology, lack of seed infection, reactions of differential genotypes, and field reactions of corn inbred lines suggest it is genetically distinct from previously described races.