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Relationships Between Yield of Three Maize Hybrids and Severity of Southern Leaf Blight Caused by Race O of Bipolaris maydis. K. J. Byrnes, Former Graduate Research Assistant, Department of Plant Pathology, University of Illinois, Urbana 61801. J. K. Pataky, and D. G. White. Associate Professor, and Associate Professor, Department of Plant Pathology, University of Illinois, Urbana 61801. Plant Dis. 73:834-840. Accepted for publication 3 May 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0834.

Southern leaf blight (SLB), caused by race O of Bipolaris maydis, adversely affected yield of three maize hybrids, B73 Mo17, FR27 Pa91, and Pioneer 3183, evaluated at nine locations. Severity of SLB in mid- to late August ranged from 05% on FR27 Pa91 at Tolono, IL, to 1040% on Pioneer 3183 at Urbana, IL. Regressions of yield on area under the curve and on severity of SLB were significant for seven, six, and four of the nine locations for Pioneer 3183, B73 Mo17, and FR27 Pa91, respectively. Yield of FR27 Pa91 and B73 Mo17 was reduced about 0.70.8% for each 1% increase in severity of SLB between 0 and 25%. For Pioneer 3183, yield was reduced about 0.60.7% for each 1% increase in severity between 0 and 25%. Yield of Pioneer 3183 decreased an additional 23% when severity increased from 25 to 40%. The effects of SLB on yield of maize varied by location, as indicated by differences in slope coefficients from regression models. Unknown factors associated with location may have influenced this relationship.

Keyword(s): corn, Helminthosporium maydis, southern corn leaf blight, Zea mays L.