Improvement of expansion volume, defined as the volume of popped corn per gram of unpopped corn, generally is considered the most important objective of popcorn (Zea mays L.) breeding programs. Popcorn, however, generally is inferior to dent corn with respect to yield and other agronomic characteristics. Detailed information on the inheritance of expansion volume and grain yield in popcorn ✕ dent corn crosses was not available in the literature. The objective of this study was to determine the inheritance of expansion volume and grain yield, including yield components, in two popcorn ✕ dent corn crosses. Generation means analysis was used to quantify genetic effects in the popcorn ✕ dent crosses Ia53 ✕ B73 and Ia28 ✕ Mo17. Significant additive genetic effects were detected for ail traits in both crosses. Significant dominance genetic effects were detected for expansion volume in the cross Ia28 ✕ Mo17, and for grain yield, ear length, ear diameter, and 5O‐kernel weight in both crosses. Dominance effects resulted in reduced expansion volume, and increased grain yield, ear length, ear diameter, and 5O‐kernel weight. Significant epistatic effects for grain yield were detected in the crosses Ia53 ✕ B73. Expansion volume was negatively correlated with all yield components except for number of kernel rows. Thus, relative to other yield components studied, selection for high kernel row number would appear to result in the least reduction of expansion volume. Results from this study indicate that breeding methodologies which exploit additive genetic variation assoicated with expansion volume and dominance variation associated with grain yield are most likely to result in concurrent improvement of these two traits.

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Dryland maize (Zea mays L.) production in the U.S. western High Plains is hampered by variable yields because of substantial environmental variation in this region. This study was conducted to determine the degree to which the ranking of superior maize hybrids for dryland production in the western High Plains was predictable from performance of the same hybrids in highly productive, irrigated environments in the same region. Forty‐five maize hybrids were evaluated for grain yield performance under different water regimes in western Nebraska, eastern Wyoming, and northeastern Colorado in 1998 and 1999. The value of genotypic variance was by far larger in fully irrigated test environments (0.70) than in nonirrigated test environments (0.01–0.17). The genotypic mean repeatability in fully irrigated test environments (0.63) compared with that in nonirrigated test environments (0.18–0.69, respectively), and it showed correspondence with yield performance. The genetic correlation between fully and nonirrigated environments (0.72) was lower than that observed between all‐nonirrigated environments (0.78–1.02). Thus, the proportion of direct advance in the former case (0.63) was generally lower than in the latter (0.41–0.97). However, an environmental similarity ratio (ESR) derived from crossover interaction indicated that water‐contrasting environments were as similar (ESR = 0.53) as nonirrigated environments (ESR = 0.49) in ranking the maize hybrids. Selective identification of maize hybrids in irrigated environments for production under nonirrigated environments in the western High Plains might be a useful surrogate to direct selection in the latter environments.

Maize (Zea mays L.) production in the western High Plains of the USA occurs under dryland and irrigated conditions. Thus, an ideal maize hybrid for this region would have stable and high average performance across environments that are highly variable in productivity. Stability of a hybrid in this research was defined as its across‐environmental variance. Nine commercial single‐cross hybrids and 36 related double crosses were evaluated for grain yield in four irrigated and eight dryland environments in Nebraska, Colorado, and Wyoming. Environmental means ranged from 2.10 to 12.01 Mg ha−1 The average superiority of the single crosses over the double crosses in mean grain yield was 11.5%. However, the double crosses were generally more stable than the single crosses. This was true regardless whether stability was measured across all 12 environments or only across the eight dryland environments. The greater stability of the double‐cross hybrids in the dryland environments was the result of fewer extremely low or high yields compared with the single crosses. Hybrids were ranked considering both stability and mean performance with a safety‐first index. Values of this index depended on the value chosen for acceptable minimal yield. Across all 12 environments, a double‐cross hybrid ranked the best when the minimal acceptable yield was <2.68 Mg ha−1, and across the eight dryland environments this happened when the minimal acceptable yield was <1.88 Mg ha−1 Possible use of other types of heterogeneous maize hybrids in the Western High Plains are discussed.

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