Breeding potential of intra- and interheterotic group, crosses in maize

New maize (Zea mays L.) inbreds are usually developed within a heterotic group. However, breeders sometimes use commercial hybrids as a nonconventional (i.e., interheterotic group) source of new inbreds. The effects of disrupting heterotic patterns in maize, by selfing from commercial hybrids, are not well understood. My objective was to compare intra- and interheterotic group crosses as sources of new inbreds. The inbreds B73 and H93 represented the Iowa Stiff Stalk Synthetic (BSSS) heterotic group, whereas Mo17 and B99 represented the non-BSSS heterotic group. I estimated testcross means and genetic variances in two intragroup F₂ populations: (B73 × H93)F₂ testcrossed to Mo17 × B99; and (Mo17 × B99)F₂ testcrossed to B73 × H93. Likewise, I estimated testcross means and genetic variances in two intergroup F₂ populations: (B73 × Mo17)F₂ testcrossed to H93 × B99; and (H93 × B99)F₂ testcrossed to B73 × Mo17. Testcrosses of 150 individual plants from each F₂ population were evaluated at three Indiana locations in 1999. Testcross means for grain yield were 1.0 Mg ha^-1 higher in the intra- than in the intergroup F₂ populations. Grain moisture and stalk lodging testcross means were lower in the intra- than in the intergroup F₂ populations. Testeross genetic variances (V_TC) for grain yield were similar among the four populations. Favorable epistatic combinations may have been broken up in the (B73 × Mo17)F₂ population. The results underscore that the success of developing new inbreds from an intergroup population largely depends on finding a suitable tester for the resulting intergroup inbreds.