In the cooler temperate regions of the world, maize (Zea mays L.) is primarily cultivated for forage usage. In this study, we mapped and characterized quantitative trait loci (QTL) affecting testcross performance of important forage maize traits and investigated their consistency across environments and testers. Two elite flint inbred lines were crossed to generate 380 F2 individuals, 345 of which were genotyped at 89 RFLP (restriction fragment length polymorphism) marker loci. The 380 F3 lines obtained by selfing the F2 individuals and the parent lines were crossed to two diverse dent inbred testers. Each series of testcrosses (TC) was evaluated in field trials with two replicates in five environments. Five traits were analyzed: dry matter yield (DMY), dry matter concentration (DMC), plant height (PHT), starch concentration (STC), and starch yield (STY). Genotypic ( trueσ^g2) and genotype × environment variances were highly significant for all traits in both TC series. Heritabilities ranged from 0.64 to 0.88 except for STY (0.46, 0.47). Genotypic correlations between testers were high (>0.80) for all traits. QTL analyses were performed by composite interval mapping. Between seven (STY) and 16 (PHT) QTL were detected in each testcross series, explaining between 52 and 71% of all in a simultaneous fit. Few QTL displayed significant interactions with environments. Results were highly consistent across testers for DMC and PHT, but not for DMY, STC, and STY. Although a comparison of TC generation means indicated significant epistasis for DMY and PHT, significant interactions between QTL were detected in two cases only. If a genomic region simultaneously affected two characters, the increasing alleles for the individual traits originated in most cases from the same parent for positively correlated traits and from different parents for negatively correlated traits.

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We mapped and characterized quantitative trait loci (QTL) affecting testcross performance of important forage maize (Zea mays L.) traits and investigated their consistency across different populations. Four independent populations comprising 380 F3 lines (A✕Bc), 113 F5 lines (A✕BV), 131 F4 lines (A✕CV), and 140 F4 lines (C✕DV) were produced from four elite flint inbreds (A, B, C, D) and genotyped at 89, 151, 104, and 122 RFLP marker loci, respectively. All lines were testcrossed to the same dent inbred tester and evaluated in field trials with two replications in five environments. Six traits were analyzed: dry matter yield (DMY), dry matter concentration (DMC), plant height (PHT), in vitro digestible organic matter (IVDOM), starch concentration (STC), and protein concentration (CPC) of forage. Genotypic variances (σ̂2g) were mostly significant for these traits in all populations and heritabilities generally exceeded 0.50. Between 2 and 14 QTL were detected in individual populations by composite interval mapping, which explained between 17.6 and 65.7% of the total phenotypic variance (σ̂2p). Few of the detected QTL displayed significant digenic epistatic or QTL ✕ environment interactions. Consistency of QTL positions across all four populations was greater for DMC, STC, and PHT than for DMY, IVDOM, and CPC. Across all traits' QTL, results were largely consistent among A✕BC and A✕Bv, but not among A✕Bc and A✕Cv or A✕Bc and C✕Dv. When QTL positions and substitution effects for DMY obtained in A✕BC, explaining 43% of σ̂2p, were employed for prediction of QTL positions and substitution effects in the other three populations they explained 24% of σ̂2p in A✕BV, 11% σ̂2p in A✕Cv, and 0% of σ̂2p in C✕DV. QTL results were poorly consistent among crosses within the flint heterotic pool, suggesting that prior to marker‐assisted selection, QTL mapping must be performed separately for each population.

Improving forage quality is a major goal in maize breeding for cooler climates. In this study, we mapped and characterized quantitative trait loci (QTL) affecting testcross (TC) performance of important forage maize quality traits and investigated their consistency across testers. Two elite flint inbred lines were crossed to generale 380 F2 individuals, 345 of which were genotyped at 89 RFLP marker loci. The 380 F3 lines produced by selfing the F2 individuals were testcrossed to two dent inbred testers. Each TC series was evaluated in field trials with two replications in five environments. The following six traits were analyzed: in vitro digestible organic matter (IVDOM), acid detergent fiber (ADF), metabolizable energy concentration (MEC), and protein concentration (CPC), all determined by near infra‐red reflectance spectroscopy (NIRS), as well as metabolizable energy yield (MEY) and protein yield (CPY). Genotypic variances (σ̂2g) mostly significant for these traits in both TC series. Heritabilities ranged from 0.24 to 0.69 and were low for IVDOM, ADF, and MEC. Genotypic correlations between testers exceeded 0.64 for each trait. Between four (CPY) and ten (CPC) QTL were detected in each TC experiment by composite interval mapping, explaining between 48.4% and 85.3% of σ̂2g in a simultaneous fit. QTL results were consistent across testers for CPC and CPY, but not for IVDOM, ADF, MEC, and MEY. Few of the detected QTL displayed significant digenic epistatic interactions. The digestibility traits IVDOM, ADF, and MEC were tightly correlated (|r̂g| > 0.88) with each other and displayed intermediate genotypic correlations (r̂g) with plant height and starch concentration, but low r̂g values with dry matter yield or dry matter concentration. In most cases, the magnitude of r̂g corresponded well with the number of common QTL regions affecting both traits.

The European corn borer (ECB), Ostrinia nubilalis Hb., is a major pest of maize in central Europe and promotes the infection of maize with Fusarium spp. In this study, transgenic Bt maize hybrids were compared with their isogenic counterparts, and with commercial hybrids from the recommended list with regard to their level of ECB resistance and their concentration of deoxynivalenol (DON), its 15‐acetyl (15‐A‐DON) and 3‐acetyl (3‐A‐DON) derivatives, nivalenol (NIV), fusarenon‐X (FUS‐X), fumonisins (FUM), and zearalenon (ZEN) in harvested grains. The field experiments were performed in Germany at four locations in 1999 and at five locations in 2000. Transgenic Bt hybrids showed significantly lower means than their corresponding isogenic counterparts and than commercial hybrids for all resistance traits: damage rating of stalks, number of larvae per plant, number of larvae per ear, and percentage of damaged plants or ears under infestation. Among all mycotoxins analysed, DON consistently showed the highest concentration across all year × location combinations. Mycotoxin concentrations varied significantly between locations, years and genotypes, whereas mycotoxin concentrations were not significantly different between infested and protected plots. Associations between ECB resistance traits and mycotoxin concentrations were not consistent across years. It is concluded that under central European conditions, the use of Bt maize hybrids will only slightly reduce the contamination of maize kernels with mycotoxins produced by Fusarium spp.