Indications from a Diallel Study for Interracial Maize Hybridization in the Corn Belt1

Yields and yield heterosis were investigated in a diallel study involving six six‐line maize ( Zea mays L.) synthetics consisting of three Corn Belt dents, a Cateto flint, and an adapted version each of Mexican dent (predominantly Tuxpeno) and Carribean flint/dent (Coastal Yellow Flint‐ETO‐Costeno). The three exotic synthetics yielded significantly less than the three Corn Belt dent synthetics (5.56 to 6.69 Mg ha −1 vs. 7.01 to 7.36 Mg ha −1 , respectively). Crosses among synthetics ranged in yield from 7.31 to 8.27 Mg ha −1 . Significant general combining ability effects indicated that additive effects were of major importance. Heterotic responses of these crosses (relative to midparent) were in the range of 112 to 115% within Corn Belt dent, 111 to 117% between the three Corn Belt synthetics and the Mexican and Caribbean synthetics, and 112% between the Mexican and Caribbean synthetics. Cateto differed from the other synthetics with a heterotic range of 123 to 128%. This pattern suggested a rather close affinity among Corn Belt, Mexican, and Carribean germplasms. The exotics lacked sufficient heterotic responses in their hybrid combinations to excel, and very seldom to equal, Corn Belt ✕ Corn Belt combinations. Little support was offered for maintaining Corn Belt dent and the other three major exotic racial complexes separately for use in interracial combinations. Rather, this evidence, plus considerations of Corn Belt dent origins, supported an incorporation approach where distinctly diverse races, such as Cateto, are combined separately with the more diverse elements of Corn Belt dent, whose derived forms can serve in recurrent selection programs.