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Disease Note

Race 23N of Exserohilum turcicum in Florida. J. K. Pataky, Department of Plant Pathology, University of Illinois, Urbana 61801. M. L. Carson, and P. R. Mosely. USDA-ARS, North Carolina State University, Raleigh 27695; and Illinois Foundation Seeds, Inc., Champaign 61820. Plant Dis. 75:863. Accepted for publication 15 May 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0863E.

Race 0 (Htl,Ht2,Ht3,HtN/0) and race 1 (Ht2,Ht3,HtN/Htl) of Exserohilum turcicum (Pass.) K.J. Leonard & E.G. Suggs are prevalent and race 23 (Htl,HtN/Ht2,Ht3) is rare in North America (D. R. Smith. Proc. 20th Annu. Corn Breeders School, 1984). Race 23N (Htl/ Ht2, Ht3, HtN) was reported from Texas and Hawaii and race 2N (Htl,Ht3/ Ht2,HtN) was found in Hawaii in 1988 (1). In May 1990, we surveyed sweet corn (Zea mays L.) breeding nurseries and hybrid trials in central Florida where many supersweet (sh2) hybrids carry the gene Htl. Lesions were collected from four fields near Belle Glade and one field near Zellwood. Of 94 isolates of E. turcicum assayed, 76 were identified as race I, 15 as race 0, I as race 23, and 2 (from different fields near Belle Glade) as race 23N. Virulence of races 23 and 23N was confirmed in independent greenhouse trials in Urbana, Illinois, and Raleigh, North Carolina. This is the first report, of which we are aware, of virulence in Florida matching the genes Ht2, Ht3, and HtN and of the occurrence of race 23N in North America other than in Texas.

Reference: (1) J. M. Windes and W. L. Pedersen. Plant Dis. 75:430, 1991.