ABSTRACT Acid soils and associated aluminum toxicity could limit maize ( Zea mays L.) production on more than 3950 million hectares worldwide. Callose formation in root tips is a reliable indicator of Al‐induced cell damage. We studied the modes of gene action determining callose formation in root tips using two diallel mating experiments involving a total of 33 maize inbred lines grown in 25 μM Al nutrient solution. Highly significant differences were found among parents, crosses, general combining ability (GCA), specific combining ability (SCA) effects, and for the contrast of parents vs. crosses in both diallel experiments. These results indicate that additive and nonadditive gene effects were important in the expression of callose content.