Evidence that Race 1 of Setosphaeria turcica Caused the 1985 Northern Corn Leaf Blight Epidemic in North Carolina. K. J. Leonard, USDA-ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27695. S. Leath, USDA-ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27695. Plant Dis. 70:981. Accepted for publication 7 May 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-981d.
An epidemic of northern leaf blight (NLB) of corn (Zea mays L.) caused by Setosphaeria turcica (Luttrell) Leonard & Suggs (anamorph Exserohilum turcicum (Pass.) Leonard & Suggs) occurred in northwestern North Carolina in 1985. Damage was severe in hybrids without the Ht1 gene for resistance to NLB. In many fields, up to 75% of the leaf area was destroyed by 15 August. Isolates of S. turcica obtained from surface-sterilized corn leaves were tested for virulence on corn seedlings with and without the Ht1 gene. Nine of 60 symptomless corn leaves, collected in another study on 16 July in a field in Yadkin County before the epidemic was apparent, yielded S. turcica isolates; all nine isolates from these leaves were race 1 (avirulent on corn with the Ht1 gene). Five fields of severely diseased corn in Yadkin. Wilkes, and Surry counties were sampled from 8 to 19 August; all 15 isolates tested were race 1. Race 2 (virulent on plants with the Ht1 gene) was first found in late August on corn hybrids with Ht1 resistance. Three leaf samples from Iredell County on 28 August yielded one race 1 and two race 2 isolates. Race 2 was found in one sample from Burke County on 29 August. Disease was less severe and appeared later in the fields from which race 2 was isolated.