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Predominance in New York of Isolates of Exserohilum turcicum Virulent on Maize with Gene Ht1. N. P. Keller, Department of Plant Pathology, Cornell University, Ithaca, NY 14853-5908. G. C. Bergstrom, Department of Plant Pathology, Cornell University, Ithaca, NY 14853-5908. Plant Dis. 74:530. Accepted for publication 23 March 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0530A.

>Exserohilum turcicum (Pass.) Leonard & Suggs, causal fungus of northern maize leaf blight, has been characterized by several physiologic races and two mating Iypes (1,2). Twenty-eight isolates of E. turcicum were collected from blighted maize (Zea mays L.) leaves in New York (representing 12 counties, predominantly in the southern tier of counties) during 1985-1987. All 28 isolates were virulent on differential maize inbreds Oh43 and Oh43 Ht1 and avirulent on Oh43 Ht2, a virulence pattern recently designated as race 1 (1). This is consistent with the widespread deployment in New York of hybrids containing gene Htl. The mating type of the isolates was determined by making sexual crosses with lester isolates of known mating type. Of seven isolates that produced fertile crosses (i.e., formation of mature perithecia containing ascospores), one was identified as mating type A and six as mating type a. The presence of both mating types within the New York population of E. turcicum suggests an increased potential for sexual recombination and evolution of new variants of the pathogen in this region.

References: (1) K. J. Leonard ct a1. Plant Dis. 73:776, 1989. (2) R. P. Thakur et al. Plant Dis. 7:151, 1989.