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Maize (Zea mays L.) is one of the most important cereal crops worldwide, and increasing the grain yield and biomass has been among the most important goals of maize production. The plant architecture can determine the grain yield and biomass to some extent; however, the genetic basis of the link between the plant architecture and grain yield/biomass is unclear. In this study, an immortal F9 recombinant inbred line population, derived from the cross Mo17 x Huangzao4, was used to detect quantitative trait loci (QTLs) for 3 traits associated with plant architecture under two nitrogen regimes: plant height, ear height, and leaf number. As a result, 8 and 10 QTLs were identified under the high nitrogen regime and low nitrogen regime, respectively. These QTLs mapped to chromosomes 1 (six QTLs), 2 (one QTL), 3 (one QTL), 7 (two QTLs), and 9 (eight QTLs), and had different genetic distances to their closest markers, ranging from 0 to 22.0 cM, explaining 4.7 to 20.5% of the phenotypic variance. Because of an additive effect, 9 and 9 could make the phenotypic values of traits increase and decrease to some extent, respectively. These results are beneficial for understanding the genetic basis of agronomic traits associated with plant architecture and for performing marker-assisted selection in maize breeding programs.

The ear leaf is one of the most important leaves in maize (Zea mays); it affects plant morphology and yield. To better understand its genetic basis, we examined ear leaf length, ear leaf width, and ear leaf area for quantitative trait locus (QTL) mapping in a recombinant inbred line population under two nitrogen regimes. Nine QTLs, on chromosomes 1 (one), 2 (one), 3 (one), 4 (three), 7 (one), and 8 (two), were mapped under the high nitrogen regime, which explained phenotypic variation ranging from 5.4 to 14.8%. Under the low nitrogen regime, 7 QTLs were located on chromosomes 1 (one), 4 (two), 7 (one), and 8 (three), which accounted for phenotypic variation ranging from 5.5 to 20.5%. These QTLs had different mapping intervals to their nearest markers, ranging from 0.3 to 21.0 cM. Due to additive effects, 3 and 13 QTLs can cause phenotypic values of these traits to increase or decrease to some extent, respectively. This information will help understand the genetic basis of ear leaf formation and will be useful for developing marker-assisted selection in maize-breeding projects.

Days to silking (DTS) is one of the most important traits in maize (Zea mays). To investigate its genetic basis, a recombinant inbred line population was subjected to high and low nitrogen (N) regimes to detect quantitative trait loci (QTLs) associated with DTS. Three QTLs were identified under the high N regime; these explained 25.4% of the phenotypic variance. Due to additive effects, the QTL on chromosome 6 increased DTS up to 0.66 days; while the other two QTLs mapped on chromosome 9 (one linked with Phi061 and the other linked with Nc134) decreased DTS 0.89 and 0.91 days, respectively. Under low N regime, two QTLs were mapped on chromosomes 6 and 9, which accounted for 25.9% of the phenotypic variance. Owing to additive effects, the QTL on chromosome 6 increased DTS 0.67 days, while the other QTL on chromosome 9 decreased it 1.48 days. The QTL on chromosome 6, flanked by microsatellite markers Bnlg1600 and Phi077, was detected under both N regimes. In conclusion, we identified four QTLs, one on chromosome 6 and three on chromosome 9. These results contribute to our understanding of the genetic basis of DTS and will be useful for developing marker-assisted selection in maize breeding programs.

Kernel number per ear (KNE) is one of the most important yield-related agronomic traits in maize (Zea mays). To clarify its genetic basis, we made a quantitative trait locus (QTL) analysis of KNE in a recombinant inbred line population derived from lines Mo17 and Huangzao4, under two nitrogen (N) regimes. Seven QTLs, on chromosomes 4, 6 and 9, were mapped under the high N regime, which explained phenotypic variation ranging from 5.03 to 15.49%. Under the low N regime, three QTLs were located on chromosomes 6 and 9, which accounted for phenotypic variation ranging from 8.54 to 12.21%. These QTLs had different mapping intervals to their nearest markers, ranging from 0 to 16.5 cM. According to the chromosome positions and genetic effects of these QTLs, only seven QTLs for KNE were identified in our experiment, out of which three were found under both N regimes, on chromosomes 6 (one) and 9 (two); the other four were mapped only under the high N regime, on chromosomes 4 (three) and 6 (one). This information could be useful for developing marker-assisted selection in maize-breeding projects.

Ear weight is one of the most important agronomic traits considered necessary in maize (Zea mays L.) breeding projects. To determine its genetic basis, a population consisting of 239 recombinant inbred lines, derived from the cross Mo17 x Huangzao4, was used to detect quantitative trait loci (QTLs) for ear weight under two nitrogen regimes. Under a high nitrogen fertilization regime, one QTL was identified in chromosome bin 2.08-2.09, which explained 7.46% of phenotypic variance and an increase in ear weight of about 5.79 g, owing to an additive effect. Under a low nitrogen regime, another QTL was identified in chromosome bin 1.10-1.11; it accounted for 7.11% of phenotypic variance and a decrease of 5.24 g in ear weight, due to an additive effect. Based on comparisons with previous studies, these two QTLs are new loci associated with ear weight in maize. These findings contribute to our knowledge about the genetic basis of ear weight in maize.