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Gene Action Conditioning Resistance to Northern Leaf Blight in Maize¹

The nature of gene action conditioning the quantitative type of resistance in maize (Zea mays L.) to Northern leaf blight caused by Helminthosporium turcicum Pass. was studied in crosses between four Australian resistant inbred lines (D21, HB, 21H, and 25) and three tester inbred lines (susceptibles H10 and 701, and moderately resistant Oh43). Populations composed of the P₁, P₂, F₁, F₂, BC₁P₁ and BC₁P₂ generations were studied for the 12 possible crosses in 1966 and with the addition of F₃, BC₁P₁S and BC₁P₂S families for four crosses in 1967.

Additive, dominance, and epistatic gene action were detected by analysis of generation means. Additive gene action was of major importance in all crosses in both years. The relative importance of non-additive effects was generally small and varied with the population involved and, to a lesser extent, with the year of study. Although biased by limitations in experimental and analytical design, estimates of components of genetic variance were in general agreement with the results of the generation mean analysis.

It was concluded that leaf blight resistance in these lines was conditioned by a relatively low number of genes, primarily additive in effect. Breeding for resistance to this disease should be effectively accomplished by such simple procedures as phenotypic recurrent selection or mass selection.

Key Words: Zea mays • Helminthosporium turcicum • Quantitative host resistance • Generation mean analysis

² Formerly Research Assistant (now Assistant Professor of Crop Science, University of Saskatchewan, Saskatoon) and Professor of Plant Pathology and Genetics, University of Illinois, Urbana. This study was conducted while the senior author held a Thomas Lawrence Pawlett Traveling Scholarship from the University of Sydney, Australia.

Received for publication May 6, 1970.