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An Isolate of Exserohilum turcicum Virulent on Maize Inbreds with Resistance Gene HtN. J. M. Windes, Department of Plant Pathology, University of Illinois, Urbana 61801. W. L. Pedersen, Department of Plant Pathology, University of Illinois, Urbana 61801. Plant Dis. 75:430. Accepted for publication 15 November 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0430E.

In 1988, J. J. Ooka at the University of Hawaii observed susceptible lesions of northern corn leaf blight caused by Exserohilum turcicum (Pass.) Leonard & Suggs on parental material of maize (Zea mays L.) containing HtN. Ten isolates of E. turcicum collected from these lesions were tested in the greenhouse on seedlings of a series of nearly isogenic inbred lines of maize (B37, B37 Ht1, B37 Ht2, B37 Ht3, and B37 HtN). Seven of the isolates were identified as race 23 (1) and two as race 23N. Isolate 24930-4, however, was virulent on B37, B37 Ht2, and B37 HtN but avirulent on B37 Ht1 and B37 Ht3. Isolate 24930-4 also was virulent on inbreds Oh45HtN, BI4AHtN, and B68HtN. Thakur et al (2) reported a new race of E. turcicum, race 4 or race 23N, collected from southern Texas that was virulent on Ht2, Ht3, and HtN. The Hawaii isolate (24930-4) differed from race 23N by inducing a resistant reaction on B37 Ht3. On the basis of these results, we propose that this isolate of E. lurcicum be designated as race 2N with the virulence formula Htl,Ht3/Ht2,HtN. The identification of this race lends support to the gene-for-gene relationship in pathosystems.

References: (1) K. J. Leonard et al. Plant Dis. 73:776, 1989. (2) R. P. Thakur et al. Plant Dis. 73: 151, 1989.