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Evaluation of Iowa Stiff Stalk Synthetic for Resistance to Gray Leaf Spot. M. J. Graham, Department of Plant and Soil Sciences, University of Delaware, Newark 19717-1303. J. A. Hawk, R. B. Carroll, J. E. Ayers, K. R. Lamkey, and A. R. Hallauer. Department of Plant and Soil Sciences, University of Delaware, Newark 19717-1303; Department of Plant Pathology, The Pennsylvania State University, University Park 16802; Field Crops Research Unit, Agricultural Research Service, U.S. Department of Agriculture; and Department of Agronomy, Iowa State University, Ames 50011. Plant Dis. 77:382-385. Accepted for publication 1 December 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0382.

Gray leaf spot (GLS) of maize (Zea mays), caused by Cercospora zeae-maydis, has become an increasing disease problem in the United States. Resistance to this pathogen is generally higher in inbred lines of Lancaster origin compared to lines derived from Iowa Stiff Stalk Synthetic (BSSS). This study was conducted to determine whether recurrent selection for yield had altered the level of GLS resistance in BSSS and to identify BSSS(R)C11 S1 lines that combine GLS resistance with high yield. The distribution of GLS ratings for S1 lines derived from BSSSC0 and BSSS(R)C11 were very similar, indicating that selection for yield had not altered GLS resistance levels. Although the mean rating for both cycles was a susceptible 7 (1 = resistant, 9 = susceptible), S1 lines with intermediate levels of resistance (46) were identified. The 250 BSSS(R)C11 S1 lines were crossed to LH51, and the testcrosses were evaluated for yield and agronomic performance. S1 lines were identified which combine intermediate levels of GLS resistance with above-average standability and yield. These S1 lines will be recombined to develop an Iowa Stiff Stalk Synthetic population adapted to eastern maize growing conditions.

Keyword(s): maize breeding.