Disease Note

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.