Published information is lacking on whether genomewide selection, based on a single tester and a single year of testing, can identify maize (Zea mays L.) lines that would perform well in multiple subsequent years and with multiple testers. Our objectives were to determine (i) if phenotypic selection or genomewide selection is more predictive of maize performance in future environments and with different testers, (ii) if combining both marker and phenotypic information is advantageous in selection, and (iii) the upward bias in correlations between marker‐predicted values and phenotypic values (rMP) when cross‐validation across individuals and across environments is not performed. We evaluated four elite populations, each with 150 or 250 doubled haploid (DH) lines, in 18 environments in the US Corn Belt. The DH lines were genotyped with 3072 single nucleotide polymorphism markers. The rMP values were 0.14 to 0.66 for grain yield and 0.49 to 0.66 for moisture. Phenotypic selection was always as effective as or more effective than genomewide selection. The rMP was lower when different testers were used for the training and test populations. Selection based on marker and phenotypic information was slightly more effective than genomewide selection or phenotypic selection alone. The correlation between predicted and observed performance was higher when cross‐validation across individuals and years was not performed than when cross‐validation across individuals and years was performed. For genomewide selection to be superior to phenotypic selection, the gains must not be measured in terms of the per‐generation response with equal population sizes and selection intensities.

Abbreviations: DH, doubled haploid; N sel , number of selected lines; RE, relative efficiency; RE Max , maximum relative efficiency; r MP , correlation between the marker-predicted performance of lines n + 1 to N in year i and the observed performance of lines n + 1 to N in years j and k; r MP(N), correlation between the marker-predicted performance of lines 1 to n in year i and the observed performance of lines 1 to n in years j and k; r P , correlation between observed performance of lines n + 1 to N in year i and the observed performance of lines n+1 to N in years j and k; SNP, single nucleotide polymorphism.

The European corn borer (ECB, Ostrinia nubilalis Hübner) is a major pest of maize (Zea mays L.) in North America and Europe. In this study, we mapped and characterized QTL affecting the resistance to the first (ECB1) and second generation (ECB2) of ECB and plant height with the aid of 164 SNP and 88 SSR markers. A total of 144 testcross (TC) progenies of double haploid (DH) lines developed from a cross of two parental lines from the Stiff Stalk germplasm pool were tested at six different locations in the USA under both natural and artificial infestation with ECB larvae. Resistance to ECB1 and ECB2 was assessed by measuring leaf feeding and stalk breakage, respectively, using a visual rating scale from 1 (severe damage) to 9 (no damage). Genotypic variance among the TC progenies was significant for all traits. Heritabilities were moderately high (0.69) for stalk breakage and plant height (0.75), but only moderate for leaf feeding (0.43). For stalk breakage, three QTL were detected that together explained 36% of the genetic variance, whereas for leaf feeding only one QTL was mapped, which explained 25% of the genotypic variance. For plant height, two QTL were identified, explaining 20% of the genotypic variance. The QTL for leaf feeding and stalk breakage mapped by us were located in chromosomal regions adjacent to those reported for other maize germplasm and therefore might be suitable candidates for marker-assisted selection (MAS) during line development.