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Although there are many new types of environmentally friendly fertilizers that can improve maize yield, chemical fertilizers are the most widespread type of fertilizer used in the agricultural sector of China due to their low cost and ease of application. However, the misuse of chemical fertilizers could lead to environmental problems, such as the massive emission of greenhouse gases (GHG). Therefore, it is important to determine how fertilizer-use efficiency (FUE) could be improved to stabilize or increase maize yield while reducing GHG emissions. In this study, we collected 6618 date records which include three datasets (for N, P, and K) from five maize-growing regions in China from 2005 to 2018, and performed a meta-analysis on the effects of N, K, and P fertilization levels on maize yield, partial factor productivity (PFP), agronomic efficiency (AE), and the carbon footprint of maize production. Additionally, scenario analyses were performed to estimate optimal fertilizer application rates for stabilizing or increasing maize yield while reducing GHG emissions. It was shown that FUE and maize yield responses to fertilization level varied in different regions. Compared to the past, the maize production of China has improved significantly in terms of FUE and its carbon footprint in recent years. Because of improvements in maize cultivars and cultivation technologies, it is possible to decrease N, P, and K application rates and reduce per unit area carbon footprint of maize, without compromising yield. In the future, N fertilization should be reduced by 10% from current levels, and the application of P and K fertilizers should be increased or decreased depending on the conditions of each maize-growing region. Thus, it should be possible to stabilize or even increase yields and reduce GHG emissions of maize production, thereby achieving green and efficient development. [ABSTRACT FROM AUTHOR]

Background: C-type cytoplasmic male sterility (CMS-C) is one of the three major types of cytoplasmic male sterility (CMS) in maize. Rf4 is a dominant restorer gene for CMS-C and has great value in hybrid maize breeding, but little information concerning its functional mechanism is known. Results: To reveal the functional mechanism of Rf4, we developed a pair of maize near-isogenic lines (NILs) for the Rf4 locus, which included a NIL_rf4 male-sterile line and a NIL_Rf4 male fertility-restored line. Genetic analysis and molecular marker detection indicated that the male fertility of NIL_Rf4 was controlled by Rf4. Whole-genome sequencing demonstrated genomic differences between the two NILs was clustered in the Rf4 mapping region. Unmapped reads of NILs were further assembled to uncover Rf4 candidates. RNA-Seq was then performed for the developing anthers of the NILs to identify critical genes and pathways associated with fertility restoration. A total of 7125 differentially expressed genes (DEGs) were identified. These DEGs were significantly enriched in 242 Gene Ontology (GO) categories, wherein 100 DEGs were involved in pollen tube development, pollen tube growth, pollen development, and gametophyte development. Homology analysis revealed 198 male fertility-related DEGs, and pathway enrichment analysis revealed that 58 DEGs were enriched in cell energy metabolism processes involved in glycolysis, the pentose phosphate pathway, and pyruvate metabolism. By querying the Plant Reactome Pathway database, we found that 14 of the DEGs were involved in the mitochondrial tricarboxylic acid (TCA) cycle and that most of them belonged to the isocitrate dehydrogenase (IDH) and oxoglutarate dehydrogenase (OGDH) enzyme complexes. Transcriptome sequencing and real-time quantitative PCR (qPCR) showed that all the above TCA cycle-related genes were up-regulated in NIL_Rf4. The results of our subsequent enzyme-linked immunosorbent assay (ELISA) experiments pointed out that the contents of both the IDH and OGDH enzymes accumulated more in the spikelets of NIL_Rf4 than in those of NIL_rf4. Conclusion: The present research provides valuable genomic resources for deep insight into the molecular mechanism underlying CMS-C male fertility restoration. Importantly, our results indicated that genes involved in energy metabolism, especially some mitochondrial TCA cycle-related genes, were associated with maize CMS-C male fertility restoration. [ABSTRACT FROM AUTHOR]

Enhancing the basal internode mechanical strength by improving the canopy light distribution of dense planting maize to reduce the lodging rate is important for establishing a high-yielding and stable population. A three-year field experiment was carried out at three densities treatments (5.25 × 104, 6.75 × 104 and 8.25 × 104 plants hm−2) × four nitrogen fertilizer treatments (0, 120, 180 and 240 kg hm−2) to study canopy light distribution and stalk lodging resistance characteristics. Results showed that grain yield was increased 3.31–14.68% under 6.75 × 104 plants hm−2 treatment compared to 5.25 × 104 plants hm−2. Meanwhile, plant morphology was altered with the increasing of planting density, light interception rate at lower-middle canopy position (0–150 cm) was decreased 15.10%, thus the mechanical strength of the basal internodes was reduced, and the lodging rate was increased 4.66% points. The formation of maize stalk lodging resistance and grain yield was promoted by the nitrogen fertilizer application. The N 180 treatment improved mechanical strength by enhancing canopy light distribution and optimizing internode quality, lodging rate was decreased 6.31–17.22% compared to the N 240 treatment while only a 0.54–7.54% reduction in grain yield, finally. Analysis the relationship between characteristic factors and mechanical strength, we found that internode plumpness (explained the 85.6% percentage of variability) was the key factor affecting basal internode mechanical strength. Our results will assist breeders in breeding lodging-resistant hybrids and agronomists improving field management practices for low lodging rate and high yield, and will be equally illuminating for other maize-producing regions. • The lower-middle canopy position light interception rate affected internode mechanical strength. • Nitrogen fertilizer management optimized canopy light distribution affecting stalk lodging resistance. • Internode plumpness was the key factor affecting internode mechanical strength. [ABSTRACT FROM AUTHOR]