Mixed inheritance model for resistance to anthracnose leaf blight in maize

A separation of the effects of major genes from effects of polygenes is important to understand genetic inheritance of quantitative traits and predict the segregation of a crossing. The inheritance mode of resistance to anthracnose leaf bligh t (ALB) caused by C. graminicola was evaluated by a mixed model. P 1, P2, F1, F2, BC1, and BC2 generations derived from four crossings between tropical maize inbred lines were used. Maximum likelihood was used to choose the best fitting inheritance model and to estimate genetic parameters. The mixed model indicated that the resistance to ALB was controlled by a major gene in all crosses and trials, and by polygenes in at least one trial. Additive and dominance effects were important for both major gene and polygenes. Both effects of the major genes were negative, indicating their contribution to disease resistance, while both effects of the polygenes were positive or negative, reflecting differences in the genetic background among inbred li nes.