Genetic Effects Estimated from Generation Means in Four Diallel Sets of Maize Inbreds1

Abstract

Genetic parameters were estimated from generation means in four types of maize (Zea mays L.) inbred lines: first cycle lines, isolated from open‐pollinated varieties; second cycle lines, isolated from either planned pedigree crosses or synthetic varieties; good lines per se; and poor line per se. Nine generations were available for each cross: parents, F1, F2, F3, backcrosses, and backcrosses selfed. Parameters estimated were additive, dominance, and digenic epistatic effects.Second‐cycle inbreds demonstrated significantly more epistasis for yield than did first‐cycle inbreds. Good and poor inbreds were similar and intermediate to first‐ and second‐cycle inbreds in the occurence of epistasis, which occurred in 30% of the crosses. Interactions of environments ✕ additive and dominance effects were significant in more than two‐thirds of the crosses. The environments ✕ epistasis interactions were significant in 25% of the cases for the poor inbreds.Dominance effects were several times larger than additive effects for all crosses. Pooling of effects over loci is discussed as the reason for disagreement with results of variance analyses. Additive ✕ additive and dominance ✕ dominance interactions were present in half the crosses of the poor inbreds. Significance of epistatic effects and additive effects was found in about the same frequency in the other types of inbreds.Correlation analyses indicated the nonepistatic model sufficient to describe the gene action, since all r values exceeded 0.9**. The full model including epistatic terms was of value in describing a particular environment, but the epistatic terms were of no value when predicting yield in one environment from trials in a different environment.