Gray leaf spot disease, caused by Cercospora zeae-maydis Tehon and Daniels, has become a significant disease in Iowa corn (Zea mays L.) production. Incidence of gray leaf spot has increased with the increased use of conservation tillage practices. The inheritance of resistance to gray leaf spot was studied via use of generation mean analyses for five crosses and via use of 100 S1 progenies developed from an F2 population. Experiments were conducted at two locations that included either natural or artificial inoculation with C. zeae-maydis spores. Additive and dominance effects were significant in nearly all instances. Heritability for gray leaf spot resistance among S1 progenies was 0.78. Because resistance seemed to be determined by additive genetic variation, it seems selection for greater resistance to gray leaf spot can be effective. In all instances, the level of gray leaf spot resistance in single-cross hybrids was improved, whether the single-cross hybrid was produced with either one or both parents having resistance. It seems single-cross hybrids will have adequate levels of resistance to gray leaf spot if at least one of the parents has resistance
