Selection environments for maize in the US western High Plains
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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 non-irrigated environments in the western High Plains might be a useful surrogate to direct selection in the latter environments.
