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    玉米遗传育种合辑Maize Genetics · Breeding · Germplasm Resources

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    Genetic dissection of ear-related traits using immortalized F2 population in maize

    GAO Ri-xin, HU Ming-jian, ZHAO Hai-ming, LAI Jin-sheng, SONG Wei-bin
    2022, 21 (9): 2492-2507.   DOI: 10.1016/j.jia.2022.07.007
    Abstract199)      PDF in ScienceDirect      

    Ear-related traits are often selection targets for maize improvement.  This study used an immortalized F2 (IF2) population to elucidate the genetic basis of ear-related traits.  Twelve ear-related traits (namely, row number (RN), kernel number per row (KNPR), ear length (EL), ear diameter (ED), ten-kernel thickness (TKT), ear weight (EW), cob diameter (CD), kernel length (KL), kernel width (KW), grain weight per ear (GW), 100-kernel weight (HKW), and grain yield per plot (GY)), were collected from the IF2 population.  The ear-related traits were comprised of 265 crosses derived from 516 individuals of the recombinant inbred lines (RILs) under two separated environments in 2017 and 2018, respectively.  Quantitative trait loci (QTLs) analyses identified 165 ear traits related QTLs, which explained phenotypic variation ranging from 0.1 to 12.66%.  Among the 165 QTLs, 19 underlying nine ear-related traits (CD, ED, GY, RN, TKT, HKW, KL, GW, and KNPR) were identified across multiple environments and recognized as reliable QTLs.  Furthermore, 44.85% of the total QTLs showed an overdominance effect, and 12.72% showed a dominance effect. Additionally, we found 35 genomic regions exhibiting pleiotropic effects across the whole maize genome, and 17 heterotic loci (HLs) for RN, EL, ED and EW were identified.  The results provide insights into genetic components of ear-related traits and enhance the understanding of the genetic basis of heterosis in maize. 

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    Heterosis and heterotic patterns of maize germplasm revealed by a multiple-hybrid population under well-watered and drought-stressed conditions
    SANG Zhi-qin, ZHANG Zhan-qin, YANG Yu-xin, LI Zhi-wei, LIU Xiao-gang, XU Yunbi, LI Wei-hua
    2022, 21 (9): 2477-2491.   DOI: 10.1016/j.jia.2022.07.006
    Abstract259)      PDF in ScienceDirect      
    Understanding the heterosis in multiple environments between different heterotic groups is of fundamental importance in successful maize breeding.  A total of 737 hybrids derived from 41 maize inbreds were evaluated over two years, with the aim of assessing the genetic diversity and their performance between heterotic groups under drought-stressed (DS) and well-watered (WW) treatments.  A total of 38 737 SNPs were employed to assess the genetic diversity.  The genetic distance (GD) between the parents ranged from 0.05 to 0.74, and the 41 inbreds were classified into five heterotic groups.  According to the hybrid performance (high yield and early maturity between heterotic groups), the heterosis and heterotic patterns of Iowa Stiff Stalk Synthetic (BSSS)×Non-Stiff Stalk (NSS), NSS×Sipingtou (SPT) and BSSS×SPT were identified to be useful options in China’s maize breeding.  The relative importance of general and specific combining abilities (GCA and SCA) suggests the importance of the additive genetic effects for grain yield traits under the WW treatment, but the non-additive effects under the DS treatment.  At least one of the parental lines with drought tolerance and a high GCA effect would be required to achieve the ideal hybrid performance under drought conditions.  GD showed a positive correlation with yield and yield heterosis in within-group hybrids over a certain range of GD.  The present investigation suggests that the heterosis is due to the combined accumulation of superior genes/alleles in parents and the optimal genetic distance between parents, and that yield heterosis under DS treatment was mainly determined by the non-additive effects.
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    Creation of two hyperactive variants of phytochrome B1 for attenuating shade avoidance syndrome in maize
    ZHAO Yong-ping, ZHAO Bin-bin, WU Guang-xia, MA Xiao-jing, WANG Bao-bao, KONG De-xin, WEI Hong-bin, WANG Hai-yang
    2022, 21 (5): 1253-1265.   DOI: 10.1016/S2095-3119(20)63466-9
    Abstract177)      PDF in ScienceDirect      
    Increasing the planting density of maize is an effective measure to improve its yield.  However, plants under high planting density tend to trigger shade avoidance syndrome (SAS), reducing lodging resistance and ultimately yield drop.  Phytochrome B
    (phyB) plays a dominant role in mediating shade avoidance response.  This study constructed two hyperactive mutated alleles of maize PHYB1: ZmPHYB1Y98F (mimicking Y104F of AtPHYB) and ZmPHYB1Y359F (mimicking Y361F of AtPHYB).  Ectopic expression of ZmPHYB1Y98F and ZmPHYB1Y359F under the control of the ZmPHYB1 promoter in the Arabidopsis phyB-9 background rendered enhanced activity on complementing the phyB-9 related phenotypes compared with ZmPHYB1WT.  Moreover, similar to the behavior of ZmPHYB1WT, ZmPHYB1Y98F and ZmPHYB1Y359F proteins are localized to the nucleus after red light exposure, and could interact with PIF proteins of maize.  In addition, expression of ZmPHYB1Y98F and ZmPHYB1Y359F variants under the control of the native ZmPHYB1 promoter attenuated SAS of maize seedlings subjected to simulated shade treatment.  It effectively reduced mature maize’s plant height and ear height in field conditions.  The results combined demonstrate the utility of ZmPHYB1Y98F and ZmPHYB1Y359F for attenuating SAS and breeding high density-tolerant varieties of maize.

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    Dissecting the genetic basis of maize deep-sowing tolerance by combining association mapping and gene expression analysis
    YANG Yue, MA Yu-ting, LIU Yang-yang, Demar LYLE, LI Dong-dong, WANG Ping-xi, XU Jia-liang, ZHEN Si-han, LU Jia-wen, PENG Yun-ling, CUI Yu, FU Jun-jie, DU Wan-li, ZHANG Hong-wei, WANG Jian-hua
    2022, 21 (5): 1266-1277.   DOI: 10.1016/S2095-3119(21)63649-3
    Abstract125)      PDF in ScienceDirect      
    Deep-sowing is an important method for avoiding drought stress in crop species, including maize.  Identifying candidate genes is the groundwork for investigating the molecular mechanism underlying maize deep-sowing tolerance.  This study evaluated four traits (mesocotyl length at 10 and 20 cm planting depths and seedling emergence rate on days 6 and 12) related to deep-sowing tolerance using a large maize population containing 386 inbred lines genotyped with 0.5 million high-quality single nucleotide polymorphisms (SNPs).  The genome-wide association study detected that 273 SNPs were in linkage disequilibrium (LD) with the genetic basis of maize deep-sowing tolerance.  The RNA-sequencing analysis identified 1 944 and 2 098 differentially expressed genes (DEGs) in two comparisons, which shared 281 DEGs.  By comparing the genomic locations of the 273 SNPs with those of the 281 DEGs, we identified seven candidate genes, of which GRMZM2G119769 encoded a sucrose non-fermenting 1 kinase interactor-like protein.  GRMZM2G119769 was selected as the candidate gene because its homologs in other plants were related to organ length, auxin, or light response.  Candidate gene association mapping revealed that natural variations in GRMZM2G119769 were related to phenotypic variations in maize mesocotyl length.  Gene expression of GRMZM2G119769 was higher in deep-sowing tolerant inbred lines.  These results suggest that GRMZM2G119769 is the most likely candidate gene.  This study provides information on the deep-sowing tolerance of maize germplasms and identifies candidate genes, which would be useful for further research on maize deep-sowing tolerance.
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    Cytological study on haploid male fertility in maize
    YANG Ji-wei, LIU Zong-hua, QU Yan-zhi, ZHANG Ya-zhou, LI Hao-chuan
    2022, 21 (11): 3158-3168.   DOI: 10.1016/j.jia.2022.07.055
    Abstract204)      PDF in ScienceDirect      
    Doubled haploid (DH) breeding technology, which relies on haploid genome doubling, is widely used in commercial maize breeding.  Spontaneous haploid genome doubling (SHGD), a more simplified and straightforward method, is gaining popularity among maize breeders.  However, the cytological mechanism of SHGD remains unclear.  This study crossed inbred lines RL36 and RL7, which have differing SHGD abilities, with inducer line YHI-1 to obtain haploid kernels.  The meiotic processes of pollen mother cells (PMCs) in the haploid plants were compared with diploid controls.  The results suggested that three main pathways, the early doubling of haploid PMCs, the first meiotic metaphase chromosomal segregation distortion, and anomaly of the second meiosis, are responsible for SHGD.  Furthermore, flow cytometry analysis of ploidy levels in leaves and PMCs from haploids and diploid controls revealed that somatic cell chromosome doubling and germ cell chromosome doubling are independent processes.  These findings provide a foundation for further studies on the underlying mechanism of SHGD, aiding the application of DH technology in maize breeding practices.  
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    Weakened carbon and nitrogen metabolisms under post-silking heat stress reduce the yield and dry matter accumulation in waxy maize
    YANG Huan, GU Xiao-tian, DING Meng-qiu, LU Wei-ping, LU Da-lei
    2020, 19 (1): 78-88.   DOI: 10.1016/S2095-3119(19)62622-5
    Abstract158)      PDF in ScienceDirect      
    Post-silking high temperature is one of the abiotic factors that affects waxy maize (Zea mays L. sinensis Kulesh) growth in southern China.  We conducted a pot trial in 2016–2017 to study the effects of post-silking daytime heat stress (35°C) on the activities of enzymes involved in leaf carbon and nitrogen metabolisms and leaf reactive oxygen species (ROS) and water contents.  This study could improve our understanding on dry matter accumulation and translocation and grain yield production.  Results indicated that decreased grain number and weight under heat stress led to yield loss, which decreased by 20.8 and 20.0% in 2016 and 2017, respectively.  High temperature reduced post-silking dry matter accumulation (16.1 and 29.5% in 2016 and 2017, respectively) and promoted translocation of pre-silking photoassimilates stored in vegetative organs, especially in leaf.  The lower leaf water content and chlorophyll SPAD value, and higher ROS (H2O2 and O2-·) content under heat stress conditions indicated accelerated senescent rate.  The weak activities of phosphoenolpyruvate carboxylase (PEPCase), Ribulose-1,5-bisphosphate carboxylase (RuBPCase), nitrate reductase (NR), and glutamine synthase (GS) indicated that leaf carbon and nitrogen metabolisms were suppressed when the plants suffered from a high temperature during grain filling.  Correlation analysis results indicated that the reduced grain yield was mainly caused by the decreased leaf water content, weakened NR activity, and increased H2O2 content.  The increased accumulation of grain weight and post-silking dry matter and the reduced translocation amount in leaf was mainly due to the increased chlorophyll SPAD value and NR activity.  Reduced PEPCase and RuBPCase activities did not affect dry matter accumulation and translocation and grain yield.  In conclusion, post-silking heat stress down-regulated the leaf NR and GS activities, increased the leaf water loss rate, increased ROS generation, and induced pre-silking carbohydrate translocation.  However, it reduced the post-silking direct photoassimilate deposition, ultimately, leading to grain yield loss.
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    Genome-wide identification and comparative analysis of drought related genes in roots of two maize inbred lines with contrasting drought tolerance by RNA sequencing
    HAO Lu-yang, LIU Xu-yang, ZHANG Xiao-jing, SUN Bao-cheng, LIU Cheng, ZHANG Deng-feng, TANG Huai-jun, LI Chun-hui, LI Yong-xiang, SHI Yun-su, XIE Xiao-qing, SONG Yan-chun, WANG Tian-yu, LI Yu
    2020, 19 (2): 449-464.   DOI: 10.1016/S2095-3119(19)62660-2
    Abstract141)      PDF in ScienceDirect      
    Drought is one of the most important abiotic stresses affecting maize growth and development and therefore resulting in yield loss.  Thus it is essential to understand molecular mechanisms of drought stress responses in maize for drought tolerance improvement.  The root plays a critical role in plants sensing water deficit.  In the present study, two maize inbred lines, H082183, a drought-tolerant line, and Lv28, a drought-sensitive line, were grown in the field and treated with different water conditions (moderate drought, severe drought, and well-watered conditions) during vegetative stage.  The transcriptomes of their roots were investigated by RNA sequencing.  There were 1 428 and 512 drought-responsive genes (DRGs) in Lv28, 688 and 3 363 DRGs in H082183 under moderate drought and severe drought, respectively.  A total of 31 Gene Ontology (GO) terms were significantly over-represented in the two lines, 13 of which were enriched only in the DRGs of H082183.  Based on results of Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis, “plant hormone signal transduction” and “starch and sucrose metabolism” were enriched in both of the two lines, while “phenylpropanoid biosynthesis” was only enriched in H082183.  Further analysis revealed the different expression patterns of genes related to abscisic acid (ABA) signal pathway, trehalose biosynthesis, reactive oxygen scavenging, and transcription factors might contribute to drought tolerance in maize.  Our results contribute to illustrating drought-responsive molecular mechanisms and providing gene resources for maize drought improvement.
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    Quantitative design of yield components to simulate yield formation for maize in China
    HOU Hai-peng, MA Wei, Mehmood Ali NOOR, TANG Li-yuan, LI Cong-feng, DING Zai-song, ZHAO Ming
    2020, 19 (3): 668-679.   DOI: 10.1016/S2095-3119(19)62661-4
    Abstract100)      PDF in ScienceDirect      
    Maize (Zea mays L.) stands prominently as one of the major cereal crops in China as well as in the rest of the world.  Therefore, predicting the growth and yield of maize for large areas through yield components under high-yielding environments will help in understanding the process of yield formation and yield potential under different environmental conditions.  This accurate early assessment of yield requires accuracy in the formation process of yield components as well.  In order to formulate the quantitative design for high yields of maize in China, yield performance parameters of quantitative design for high grain yields were evaluated in this study, by utilizing the yield performance equation with normalization of planting density.  Planting density was evaluated by parameters including the maximum leaf area index and the maximum leaf area per plant.  Results showed that the variation of the maximum leaf area per plant with varying plant density conformed to the Reciprocal Model, which proved to have excellent prediction with root mean square error (RMSE) value of 5.95%.  Yield model estimation depicted that the best optimal maximum leaf area per plant was 0.63 times the potential maximum leaf area per plant of hybrids.  Yield performance parameters for different yield levels were quantitatively designed based on the yield performance equation.  Through validation of the yield performance model by simulating high yields of spring maize in the Inner Mongolia Autonomous Region and Jilin Province, China, and summer maize in Shandong Province, the yield performance equation showed excellent prediction with the satisfactory mean RMSE value (7.72%) of all the parameters.  The present study provides theoretical support for the formulation of quantitative design for sustainable high yield of maize in China, through consideration of planting density normalization in the yield prediction process, providing there is no water and nutrient limitation.
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    Interacting leaf dynamics and environment to optimize maize sowing date in North China Plain
    TIAN Bei-jing, ZHU Jin-cheng, LIU Xi-wei, HUANG Shou-bing, WANG Pu
    2020, 19 (5): 1227-1240.   DOI: 10.1016/S2095-3119(19)62831-5
    Abstract94)      PDF in ScienceDirect      
    Leaf growth and its interaction with the growing environment critically affect leaf area, distribution, and function, and ultimately affects grain yield of maize (Zea mays L.).  To detect the effects of leaf area dynamics, growth periods, and the environment on maize grain yield, a three-year field experiment was conducted using two maize varieties, medium plant-size variety Zhengdan 958 (ZD958) and large plant-size variety Zhongnongda 4 (ZND4), and three to five sowing dates.  The sowing date significantly affected maize yield as a result of changes in leaf area, growth stage, and growing environment.  Prior to the 12th leaf stage, significant correlations between leaf area dynamics, environment, and yield were seldom detected.  The expansion of leaf area from 12th leaf stage to silking stage was significantly positively correlated with growing degree days (GDD), solar radiation, and grain yield, indicating the importance of leaf area dynamics during this period.  After silking, solar radiation played a more important role in inducing leaf senescence than GDD, particularly in the 2nd half of the grain filling stage.  Accelerated leaf senescence in late growth period can increase maize yield.  The environment affected leaf area dynamics and yield of the large plant-size variety (ZND4) more easily than the medium plant-size variety (ZD958) at the optimum plant density, reflecting the difference in varietal capacity to adapt to the growing environment.  This study indicates that optimizing the interaction among leaf area dynamics, growth periods, and environment is a sound strategy to increase maize yield.  Favorable interactions are useful to determine the optimal sowing date of a given variety.
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    The effect of amylose on kernel phenotypic characteristics, starch-related gene expression and amylose inheritance in naturally mutated high-amylose maize
    ZHANG Xu-dong, GAO Xue-chun, LI Zhi-wei, XU Lu-chun, LI Yi-bo, ZHANG Ren-he, XUE Ji-quan, GUO Dong-wei
    2020, 19 (6): 1554-1564.   DOI: 10.1016/S2095-3119(19)62779-6
    Abstract108)      PDF in ScienceDirect      
    High-amylose maize starch has great potential for widespread industrial use due to its ability to form strong gels and film and in the food processing field, thus serving as a resistant starch source.  However, there is still a substantial shortage of high-amylose maize due to the limitation of natural germplasm resources, although the well-known amylose extender (ae) gene mutants have been found to produce high-amylose maize lines since 1948.  In this context, high-amylose maize lines (13 inbreds and 18 hybrids) originating from a natural amylose mutant in our testing field were utilized to study the correlation between amylose content (AC) and phenotypic traits (kernel morphology and endosperm glossiness), grain filling characteristics, gene expression, and amylose inheritance.  Our results showed that AC was negatively correlated with total starch content but was not correlated with grain phenotypes, such as kernel fullness, kernel morphology and endosperm glossiness.  Maize lines with higher amylose had a greater grain filling rate than that of the control (B73) during the first 20 days after pollination (DAP).  Both starch debranching enzyme (DBE) groups and starch branching enzyme IIb (SBEIIb) groups showed a greater abundance in the control (B73) than in the high-amylose maize lines.  Male parents directly predicted AC of F1, which was moderately positively correlated with the F2 generation.
     
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    Effects of urea mixed with nitrapyrin on leaf photosynthetic and senescence characteristics of summer maize (Zea mays L.) waterlogged in the field
    REN Bai-zhao, HU Juan, ZHANG Ji-wang, DONG Shu-ting, LIU Peng, ZHAO Bin
    2020, 19 (6): 1586-1595.   DOI: 10.1016/S2095-3119(19)62725-5
    Abstract91)      PDF in ScienceDirect      
    Waterlogging is one of the major abiotic stresses in agricultural crop production.  However, the application of 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) can effectually mitigate the losses of nitrogen efficiency and grain yield of summer maize induced by waterlogging.  In order to explore its role to alleviate waterlogging stress on leaf antioxidative system and photosynthetic characteristics of summer maize, a field experiment was executed to research effects of nitrapyrin application on leaf photosynthetic and senescent characteristics of waterlogged summer maize Denghai 605 (DH605) and Zhengdan 958 (ZD958).  Experimental treatments consisted of waterlogging treatment that was applying only urea (WL), waterlogging treatment that was applying urea mixing with nitrapyrin (WL-N), and no waterlogging treatment that was only applying urea (NWL).  Results showed that WL significantly decreased leaf area index (LAI), SPAD, photosynthetic rate (Pn), and protective enzyme activities, accelerated leaf aging, eventually led to a remarkable yield reduction by 38 and 42% for DH605 and ZD958, respectively, compared to NWL.  However, the application of nitrapyrin was useful for relieving waterlogging damages on leaf photosynthetic ability.  LAI, SPAD and Pn of WL-N for DH605 were 10, 19 and 12–24% higher, and for ZD958 were 12, 23 and 7–25% higher, compared to those of WL, respectively.  Moreover, application of nitrapyrin effectually relieved waterlogging losses on antioxidative enzyme activities.  Leaf superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities of WL-N were averagely increased by 24, 15 and 30%, respectively, while malondialdehyde (MDA) content was averagely decreased by 13%, compared to those of WL.  Visibly, nitrapyrin application could improve leaf photosynthetic characteristics and retard leaf aging induced by waterlogging, thereby leading to a yield increase of waterlogged maize.
     
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    Integrated agronomic practices management improved grain formation and regulated endogenous hormone balance in summer maize (Zea mays L.)
    YU Ning-ning, ZHANG Ji-wang, LIU Peng, ZHAO Bin, REN Bai-zhao
    2020, 19 (7): 1768-1776.   DOI: 10.1016/S2095-3119(19)62757-7
    Abstract115)      PDF in ScienceDirect      
    Compared with single agronomic practices management during grain formation, knowledge about integrated agronomic practices management on grain-filling characteristics and physiological function of endogenous hormones was limited.  In order to clarify this issue, two field experiments, integrated agronomic practices management (IAPM), T1 (local conventional cultivation practices), T2 (an optimized combination of cropping systems and fertilizer treatment), T3 (treatment based on high-yield studies), and T4 (further optimized combination of cropping systems and fertilizer treatment), and nitrogen rate testing (NAT) (four nitrogen rates, 0, 129.0, 184.5, and 300.0 kg N ha–1) were performed with summer maize hybrid Zhengdan 958 (ZD958). Results showed that with increased nitrogen rate, the endogenous hormone balance was promoted and the grain-filling characteristics were improved sufficiently to resulting in a significant increase in grain yield.  However, the grain-filling characteristics deteriorated and yield was reduced with excessive nitrogen fertilization.  However, IAPM could promote hormone balance and improve grain filling characteristic.  The indole-3-acetic acid (IAA), zeatin riboside (ZR), and gibberellin (GA3) contents under T2 and T4 treatments were higher and the abscisic acid (ABA) content was lower, and the ZR and GA3 contents under T3 were higher than those under T1.  Those resulted in the maximum grain-filling rate (Wmax) and the active grain-filling period (P) under T2, T3 and T4 were significantly increased than those under T1, and hence promoted kernel weight and grain yield.  So IAPM promoted hormone balance by improving tillage model, optimizing fertilizer rate and fertilization period, appropriately increasing planting density and delaying harvest, which promoted grain filling rate and lengthened active grain-filling period, finally increased grain yield.
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    Characterization and map-based cloning of miniature2-m1, a gene controlling kernel size in maize
    GUAN Hai-ying, DONG Yong-bin, LU Shou-ping, LIU Tie-shan, HE Chun-mei, LIU Chun-xiao, LIU Qiang, DONG Rui, WANG Juan, LI Yu-ling, QI Shi-jun, WANG Li-ming
    2020, 19 (8): 1961-1973.   DOI: 10.1016/S2095-3119(19)62797-8
    Abstract140)      PDF in ScienceDirect      
    Kernel development plays an important role in determining kernel size in maize.  Here we present the cloning and characterization of a maize gene, nitrate transporter1.5 (NRT1.5), which controls small kernel phenotype by playing an important role in kernel development.  A novel recessive small kernel mutant miniature2-m1 (mn2-m1) was isolated from self-pollinated progenies of breeding materials.  The mutant spontaneously showed small kernel character arresting both embryo and endosperm development at an early stage after pollination.  Utilizing 21 polymorphic SSR markers, the mn2-m1 locus was limited to a 209.9-kb interval using 9 176 recessive individuals of a BC1 segregating population from mn2-m1/B73.  Only one annotated gene was located in this 209.9 kb region, Zm00001d019294, which was predicted to encode nitrate transporter1.5 (NRT1.5).  Allelism tests confirmed that mn2-m1 was allelic to miniature2-m2 (mn2-m2) and miniature2-710B (mn2-710B).  The mn2-m1 and mn2-m2 alleles both had nucleotide deletions in the coding region resulting in premature termination, and the mn2-710B allele had some missence mutations.  Subcellular localization showed that Miniature 2 (MN2) is localized in the plasma membrane.  Quantitative real-time PCR (qRT-PCR) analysis revealed that the expression of MN2 and some genes involved in the basal endosperm transfer layer (BETL) and embryo surrounding region (ESR) development were affected in mn2-m1 seeds.  These results suggested that MN2 plays an important role in maize seed development.
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    Functional polymorphism among members of abscisic acid receptor family (ZmPYL) in maize
    LU Feng-zhong, YU Hao-qiang, LI Si, LI Wan-chen, ZHANG Zhi-yong, FU Feng-ling
    2020, 19 (9): 2165-2176.   DOI: 10.1016/S2095-3119(19)62802-9
    Abstract124)      PDF in ScienceDirect      
    Pyrabactin resistance 1-like proteins (PYLs) are direct receptors of abscisic acid (ABA).  For the redundant and polymorphic functions, some members of the PYL family interact with components of other signaling pathways.  Here, 253 positive colonies from a maize cDNA library were screened as interacting proteins with the members of ZmPYL family.  After sequencing and function annotation, 17 of 28 interaction combinations were verified by yeast two-hybrid (Y2H).  The germination potential, taproot length and proline content of a quartet mutant of Arabidopsis PYL genes were significantly deceased comparing to the wild type (WT) under alkaline stress (pH 8.5) and 100 μmol L–1 methyl jasmonate (MeJA) induction.  The malondialdehyde (MDA) content was significantly increased.  After germinating in darkness, the characteristics of dark morphogenesis of the quartet mutant seedlings were more obvious than those of the WT.  The differential expression of the related genes of photomorphogenesis in the mutant was much more than that in the WT.  Three light and two JA responsive cis-affecting elements were identified during the promoter sequences of the AtPYL1 and AtPYL2 genes.  These results suggested that functional polymorphism has evolved among the members of ZmPYL family.  In response to developmental and environmental stimuli, they not only function as direct ABA receptors but also interact with components of other signaling pathways mediated JA, brassinosteroid (BR), auxin, etc., and even directly regulate downstream stress-related proteins.  These signaling pathways can interact at various crosstalk points and different levels of gene expression within a sophisticated network.
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    Evaluation of drought tolerance in ZmVPP1-overexpressing transgenic inbred maize lines and their hybrids
    JIA Teng-jiao, LI Jing-jing, WANG Li-feng, CAO Yan-yong, MA Juan, WANG Hao, ZHANG Deng-feng, LI Hui-yong
    2020, 19 (9): 2177-2187.   DOI: 10.1016/S2095-3119(19)62828-5
    Abstract99)      PDF in ScienceDirect      
    The vacuolar proton-pumping pyrophosphatase gene (VPP) is often used to enhance plant drought tolerance via genetic engineering.  In this study, the drought tolerance of four transgenic inbred maize lines overexpressing ZmVPP1 (PH4CV-T, PH6WC-T, Chang7-2-T, and Zheng58-T) and their transgenic hybrids was evaluated at various stages.  Under normal and drought conditions, the height and fresh weight were greater for the four transgenic inbred maize lines than for the wild-type (WT) controls at the germination and seedling stages.  Additionally, the transgenic plants exhibited enhanced photosynthetic efficiency at the seedling stage.  In irrigated and non-irrigated fields, the four transgenic lines grew normally, but with increased ear weight and yield compared with the WT plants.  Moreover, the ear weight and yield of the transgenic hybrids resulting from the PH4CV-T×PH6WC-W and Chang7-2-T×Zheng58-W crosses increased in the non-irrigated field.  Our results demonstrated that the growth and drought tolerance of four transgenic inbred maize lines with improved photosynthesis were enhanced by the overexpression of ZmVPP1.  Moreover, the Chang7-2 and PH4CV transgenic lines may be useful for future genetic improvements of maize hybrids to increase drought tolerance.
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    Effects of post-silking water deficit on the leaf photosynthesis and senescence of waxy maize
    YE Yu-xiu, WEN Zhang-rong, YANG Huan, LU Wei-ping, LU Da-lei
    2020, 19 (9): 2216-2228.   DOI: 10.1016/S2095-3119(20)63158-6
    Abstract114)      PDF in ScienceDirect      
    Waxy maize is widely cultivated under rainfed conditions and frequently suffers water shortage during the late growth stage.  In this study, a pot trial was conducted to examine the effects of post-silking drought on leaf photosynthesis and senescence and its influence on grain yield.  Two waxy maize hybrids, Suyunuo 5 (SYN5) and Yunuo 7 (YN7), were grown under the control and drought (soil moisture content was 70–80% and 50–60%, respectively) conditions after silking in 2016 and 2017.  The decrease in yield was 11.1 and 15.4% for YN7 and SYN5, respectively, owing to the decreased grain weight and number.  Post-silking dry matter accumulation was reduced by 27.2% in YN7 and 26.3% in SYN5.  The contribution rate of pre-silking photoassimilates transferred to grain yield was increased by 15.6% in YN7 and 10.2% in SYN5, respectively.  Post-silking drought increased the malondialdehyde content, but decreased the contents of water, soluble protein, chlorophyll, and carotenoid in the leaves.  The weakened activities of enzymes involved in photosynthesis (ribulose-1,5-bisphosphate carboxylase and phosphoenolpyruvate carboxylase) and antioxidant system (catalase, superoxide dismutase and peroxidase) reduced the photosynthetic rate (Pn) and accelerated leaf senescence.  The correlation results indicated that reduced Pn and catalase activity and increased malondialdehyde content under drought conditions induced the decrease of post-silking photoassimilates deposition, ultimately resulted in the grain yield loss.
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    Key indicators affecting maize stalk lodging resistance of different growth periods under different sowing dates
    WANG Qun, XUE Jun, CHEN Jiang-lu, FAN Ying-hu, ZHANG Guo-qiang, XIE Rui-zhi, MING Bo, HOU Peng, WANG Ke-ru, LI Shao-kun
    2020, 19 (10): 2419-2428.   DOI: 10.1016/S2095-3119(20)63259-2
    Abstract144)      PDF in ScienceDirect      
    The accurate evaluation of maize stalk lodging resistance in different growth periods enables timely management of lodging risks and ensures stable and high maize yields.  Here, we established five different sowing dates to create different conditions for maize growth.  We evaluated the effects of the different growth conditions on lodging resistance by determining stalk morphology, moisture content, mechanical strength and dry matter, and the relationship between stalk breaking force and these indicators during the silking stage (R1), milk stage (R3), physiological maturity stage (R6), and 20 days after R6.  Plant height at R1 positively affected stalk breaking force.  At R3, the coefficient of ear height and the dry weight per unit length of basal internodes were key indicators of stalk lodging resistance.  At R6, the key indicators were the coefficient of the center of gravity height and plant fresh weight.  After R6, the key indicator was the coefficient of the center of gravity height.  The crushing strength of the fourth internode correlated significantly and positively with the stalk breaking force from R1 to R6, which indicates that crushing strength is a reliable indicator of stalk mechanical strength.  These results suggest that high stalk strength and low ear height benefit lodging resistance prior to R6.  During and after R6, the coefficient of the center of gravity height and the mechanical strength of basal internodes can be used to evaluate plant lodging resistance and the appropriate time for harvesting in fields with a high lodging risk.
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    Kernel crack characteristics for X-ray computed microtomography (μCT) and their relationship with the breakage rate of maize varieties
    DONG Peng-fei, XIE Rui-zhi, WANG Ke-ru, MING bo, HOU Peng, HOU Jun-feng, XUE Jun, LI Chao-hai, LI shao-kun
    2020, 19 (11): 2680-2689.   DOI: 10.1016/S2095-3119(20)63230-0
    Abstract100)      PDF in ScienceDirect      
    The most significant problem of maize grain mechanical harvesting quality in China at present is the high grain breakage rate (BR).  BR is often the key characteristic that is measured to select hybrids desirable for mechanical grain harvesting.  However, conventional BR evaluation and measurement methods have challenges and limitations.  Microstructural crack parameters evaluation of maize kernel is of great importance to BR.  In this connection, X-ray computed microtomography (μ-CT) has proven to be a quite useful method for the assessment of microstructure, as it provides important microstructural parameters, such as object volume, surface, surface/volume ratio, number of closed pores, and others.  X-ray computed microtomography is a non-destructive technique that enables the reuse of samples already measured and also yields bidimensional (2D) cross-sectional images of the sample as well as volume rendering.  In this paper, six different maize hybrid genotypes are used as materials, and the BR of the maize kernels of each variety is tested in the field mechanical grain harvesting, and the BR is used as an index for evaluating the breakage resistance of the variety.  The crack characteristic parameters of kernel were detected by X-ray micro-computed tomography, and the relationship between the BR and the kernel crack characteristics was analyzed by stepwise regression analysis.  Establishing a relationship between crack characteristic parameters and BR of maize is vital for judging breakage resistance.  The results of stepwise multiple linear regression (MLR) showed that the crack characteristics of the object surface, number of closed pores, surface of closed pores, and closed porosity percent were significantly correlated to the BR of field mechanical grain harvesting, with the standard partial regression coefficients of –0.998, –0.988, –0.999, and –0.998, respectively.  The R2 of this model was 0.999.  Results validation showed that the Stepwise MLR Model could well predict the BR of maize based on these four variables. 
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    Giving maize an excited start – Effects of dopamine on maize germination
    CHENG Hang-yuan, WANG Xing, FENG Tian-yu, PENG Chuan-xi, WANG Wei, YANG Mu-yu, ZHOU Yu-yi
    2020, 19 (11): 2690-2698.   DOI: 10.1016/S2095-3119(20)63252-X
    Abstract118)      PDF in ScienceDirect      
    Dopamine (DA) is a neurotransmitter which takes charge of brain activities about memory and self-stimulation behavior in animals.  Interestingly, our results suggest that DA could also give maize an “excited state”.  The results showed that 1  mmol L–1 DA promoted maize germination by 23.2% significantly, and accelerated the growth rate of roots and shoots by 21.4 and 24.7%, respectively.  As we all known, abscisic acid (ABA) is the key hormone involved in seed dormancy.  In our research, ABA levels in roots and shoots dramatically decreased by 16.45 and 57.57%, respectively.  To further investigate how DA reduces the ABA level in budding seed, we studied ABA synthesis and catabolism pathway.  Specific expression of key ABA-synthesis genes, such as ZmNCED1, ZmNCED3 and ZmZEP were down-regulated by DA.  Simultaneously, the expression levels of ABA8OX1a and ABA8OX1b which are major transcripts of ABA 8´-hydroxylase in ABA catabolism were up-regulated at least 1.5- and 4.6-fold, respectively.  Our results enriched the functions of animal hormones in plants.
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    Innovation of the double-maize cropping system based on cultivar growing degree days for adapting to changing weather conditions in the North China Plain
    WANG Dan, LI Guo-rui, ZHOU Bao-yuan, ZHAN Ming, CAO Cou-gui, MENG Qing-feng, XIA Fei, MA Wei, ZHAO Ming
    2020, 19 (12): 2997-3012.   DOI: 10.1016/S2095-3119(20)63213-0
    Abstract83)      PDF in ScienceDirect      
    Double-maize cropping system is an effective option for coping with climate change in the North China Plain.  However, the effects of changes in climate on the growth and yield of maize in the two seasons are poorly understood.  Forty-six cultivars of maize with different requirements for growing degree days (GDD), categorized as high (H), medium (M) or low (L), and three cultivar combinations for two seasons as LH (using JD27 and DMY1 from category L in the first season; and YD629 and XD22 from category H in the second season), MM (using JX1 and LC3 from category M in the first season; and ZD958 and JX1 from category M in the second season) and HL (using CD30 and QY9 from category H in the first season; and XK10 and DMY3 from category L in the second season) were tested to examine the eco-physiological determinants of maize yield from 2015 to 2017.  The correlations between the combinations of cultivars and grain yield were examined.  The combination LH produced the highest annual grain yield and total biomass, regardless of the year.  It was followed, in decreasing order, by MM and HL.  Higher grain yield and biomass in LH were mainly due to the greater grain yield and biomass in the second season, which were influenced mainly by the lengths of the pre- and post-silking periods and the rate of plant growth (PGR).  Temperature was the primary factor that influenced dry matter accumulation.  In the first season, low temperatures during pre-silking decreased both the duration and PGR in LH, whereas high temperatures during post-silking decreased the PGR in MM and HL, resulting in no significant differences in biomass being observed among the three combinations.  In the second season, high temperatures decreased both the PGR and pre- and post-silking duration in MM and HL, and consequently, the biomass of those two combinations were lower than that in LH.  Moreover, because of lower GDD and radiation in the first season and higher grain yield in the second season, production efficiency of temperature and radiation (Ra) was the highest in LH.  More importantly, differences in temperature and radiation in the two seasons significantly affected the rate and duration of growth in maize, and thereby affecting both dry matter and grain yield.  Our study indicated that the combination of LH is the best for optimizing the double-maize system under changing climatic conditions in the North China Plain.
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    N, P and K use efficiency and maize yield responses to fertilization modes and densities
    LI Guang-hao, CHENG Qian, LI Long, LU Da-lei, LU Wei-ping
    2021, 20 (1): 78-86.   DOI: 10.1016/S2095-3119(20)63214-2
    Abstract125)      PDF in ScienceDirect      
    Optimal planting density and proper fertilization method are important factors to improve maize yield and nutrient utilization.  A two-year (2016 and 2017) field experiment was conducted with three plant densities (6.0, 7.5 and 9.0 plants m−2) and three fertilization modes (no fertilizer, 0F; one-off application of slow-released fertilizer, SF; twice application of conventional fertilizer, CF).  Results indicated that the grain yields and N, P and K use efficiencies under SF with the optimal planting density (7.5 plants m−2) were the highest among all the treatments in 2016 and 2017.  Compared with CF, SF could increase post-silking dry matter accumulation and promote N, P and K uptake at pre- and post-silking stages; this treatment increased grain N, P and K concentrations and resulted in high N, P and K use efficiencies.  Nutrient (N, P and K) absorption efficiencies and partial productivity, and nutrient (N and P) recovery efficiency in SF treatment were significantly higher than those in CF treatments under the planting density of 7.5 plants m−2.  Under both SF and CF conditions, the grain yield, total N accumulation and nutrient use efficiencies initially increased, peaked at planting density of 7.5 plants m−2, and then decreased with increasing plant density.  Based on the yield and nutrient use efficiency in two years, plant density of 7.5 plants m−2 with SF can improve both the grain yield and N, P and K use efficiency of spring maize in Jiangsu Province, China.
     
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    Metabolic responses to combined water deficit and salt stress in maize primary roots
    LI Peng-cheng, YANG Xiao-yi, WANG Hou-miao, PAN Ting, YANG Ji-yuan, WANG Yun-yun, XU Yang, YANG Ze-feng, XU Chen-wu
    2021, 20 (1): 109-119.   DOI: 10.1016/S2095-3119(20)63242-7
    Abstract104)      PDF in ScienceDirect      
    Soil water deficit and salt stress are major limiting factors of plant growth and agricultural productivity.  The primary root is the first organ to perceive the stress signals for drought and salt stress.  In this study, maize plant subjected to drought, salt and combined stresses displayed a significantly reduced primary root length relative to the control plants.  GC-MS was used to determine changes in the metabolites of the primary root of maize in response to salt, drought and combined stresses.  A total of 86 metabolites were measured, including 29 amino acids and amines, 21 organic acids, four fatty acids, six phosphoric acids, 10 sugars, 10 polyols, and six others.  Among these, 53 metabolites with a significant change under different stresses were identified in the primary root, and the content of most metabolites showed down-accumulation.  A total of four and 18 metabolites showed significant up- and down-accumulation to all three treatments, respectively.  The levels of several compatible solutes, including sugars and polyols, were increased to help maintain the osmotic balance.  The levels of metabolites involved in the TCA cycle, including citric acid, ketoglutaric acid, fumaric acid, and malic acid, were reduced in the primary root.  The contents of metabolites in the shikimate pathway, such as quinic acid and shikimic acid, were significantly decreased.  This study reveals the complex metabolic responses of the primary root to combined drought and salt stresses and extends our understanding of the mechanisms involved in root responses to abiotic tolerance in maize.
     
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    Difference in corn kernel moisture content between pre- and post-harvest
    LI Lu-lu, MING Bo, XUE Jun, GAO Shang, WANG Ke-ru, XIE Rui-zhi, HOU Peng, LI Shao-kun
    2021, 20 (7): 1775-1782.   DOI: 10.1016/S2095-3119(20)63245-2
    Abstract89)      PDF in ScienceDirect      
    The harvest method of shelling corn (Zea mays L.) kernels in the field decreases labor costs associated with transporting, drying and threshing the crop.  However,  it was previously found that the kernel moisture content increased after field harvest, which decreased the value of corn kernels.  To identify the reasons underlying the increase, we conducted a multi-year and -area trial in the Huang-Huai-Hai Plain, China and performed a staged-harvest test at several phases of kernel dry-down.  The test investigated a range of parameters such as the kernel moisture content pre- and post-harvest, the kernel breakage rate, the amount of impurities, and the moisture content of various other plant tissues.  An analysis of 411 pairs of pre- and post-harvest samples found that kernel moisture content after harvest was 2.2% higher than that before harvest.  In the staged-harvest test, however, a significant increase was only observed when the kernel moisture content before harvest was higher than 23.9%.  The increase in post-harvest kernel moisture content was positively associated with the pre-harvest kernel moisture content, breakage rate and impurity rate.  Typically, at harvest time in this region, there is a significant fraction of immature crops with a high moisture content, resulting in kernels that are prone to breakage or impurities that ultimately lead to increases in water content after harvest.  Therefore, we suggest using hybrids that quickly wither late in the growing stage.  Additionally, farmers should delay harvest in order to minimize the pre-harvest kernel moisture content and thus reduce breakages and impurities, thereby improving the quality of kernels after harvest and the efficiency of corn kernel farming in China.
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    The effect of elevating temperature on the growth and development of reproductive organs and yield of summer maize
    SHAO Rui-xin, YU Kang-ke, LI Hong-wei, JIA Shuang-jie, YANG Qing-hua, ZHAO Xia, ZHAO Ya-li, LIU Tian-xu
    2021, 20 (7): 1783-1795.   DOI: 10.1016/S2095-3119(20)63304-4
    Abstract92)      PDF in ScienceDirect      
    Compared to other crops, maize production demands relatively high temperatures. However, temperatures exceeding 35°C lead to adverse effects on maize yield.  High temperatures (≥35°C) are consistently experienced by summer maize during its reproductive growth stage in the North China Plain, which is likely to cause irreversible crop damage.  This study investigated the effects of elevating temperature (ET) treatment on the yield component of summer maize, beginning at the 9th unfolding leaf stage and ending at the tasseling stage.  Results demonstrated that continuous ET led to a decrease in the elongation rate and activity of silks and an elongated interval between anthesis and silking stages, and eventually decreased grain number at ear tip and reduced yield.  Although continuous ET before tasseling damaged the anther structure, reduced pollen activity, delayed the start of the pollen shedding stage, and shortened the pollen shedding time, it was inferred, based on phenotypical and physiological traits, that continuous ET after the 9th unfolding leaf stage influenced ears and therefore may have more significant impacts.  Overall, when maize plants were exposed to ET treatment in the ear reproductive development stage, the growth of ears and tassels was blocked, which increased the occurrence of barren ear tips and led to large yield losses.
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    Comparative transcriptome analysis of different nitrogen responses in low-nitrogen sensitive and tolerant maize genotypes
    DU Qing-guo, YANG Juan, Shah SYED MUHAMMAD SADIQ, YANG Rong-xin, YU Jing-juan, LI Wen-xue
    2021, 20 (8): 2043-2055.   DOI: 10.1016/S2095-3119(20)63220-8
    Abstract171)      PDF in ScienceDirect      
    Although previous researches have greatly increased our general knowledge on plant responses to nitrogen (N) stress, a comprehensive understanding of the different responses in crop genotypes is still needed.  This study evaluated 304 maize accessions for low-N tolerance under field conditions, and selected the low-N sensitive Ye478 and low-N tolerant Qi319 for further investigations.  After a 5-day low-N treatment, the typical N-deficient phenotype with yellowing older leaves was observed in Ye478 but not in Qi319.  After the 5-day low-N stress, 16 RNA libraries from leaf and root of Ye478 and Qi319 were generated.  The differentially expressed genes (DEGs) in the root of Qi319 up-regulated by special N deficiency were mainly enriched in energy-related metabolic pathways, including tricarboxylic acid metabolic process and nicotinamide metabolic process.  Consistent with yellowing older leaves only observed in Ye478, the special N deficiency-responsive DEGs related to thylakoid, chloroplast, photosynthetic membrane, and chloroplast stroma pathways were repressed by low-N stress in Ye478.  A total of 216 transcription factors (TFs), including ZmNLP5, were identified as special N deficiency-responsive TFs between Qi319 and Ye478, indicating the importance of transcriptional regulation of N stress-responsive pathway in different tolerance to low-N stress between crop genotypes.  In addition, 15 miRNAs were identified as DEGs between Qi319 and Ye478.  Taken together, this study contributes to the understanding of the genetic variations and molecular basis of low-N tolerance in maize.
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    Lignin metabolism regulates lodging resistance of maize hybrids under varying planting density
    LI Bin, GAO Fei, REN Bai-zhao, DONG Shu-ting, LIU Peng, ZHAO Bin, ZHANG Ji-wang
    2021, 20 (8): 2077-2089.   DOI: 10.1016/S2095-3119(20)63346-9
    Abstract168)      PDF in ScienceDirect      
    Hybrids and planting density are the main factors affecting maize lodging resistance.  Here, we aimed to elucidate the mechanism of the regulation of maize lodging resistance by comparing two hybrids at various planting densities from the perspective of lignin metabolism.  Our results showed that compared to lodging-susceptible hybrid Xundan 20 (XD20), lodging-resistant hybrid Denghai 605 (DH605) showed a lower center of gravity and culm morphological characteristics that contributed to the higher lodging resistance of this hybrid.  Lignin content, activities of key lignin synthesis-related enzymes and G-, S- and H-type monomer contents were significantly higher in hybrid DH605 than in hybrid XD20.  Stalk mechanical strength, lignin accumulation and enzyme activity decreased significantly with increasing planting density in the two hybrids.  While G-type monomers first decreased with increasing planting density but then remained stable, S-type monomers showed a decreasing trend, and H-type monomers showed an increasing trend.  Correlation analysis showed that lodging rate was significantly correlated with plant traits and lignin metabolism.  Therefore, maize hybrids characterized by high lignin accumulation, high lignin synthesis-related activities, high S-type monomer content, low center of gravity, high stem puncture strength, high cortical thickness, and small vascular bundle area are more resistant to lodging.  High planting densities reduce stalk lignin accumulation, relevant enzyme activities and mechanical strength, thereby, ultimately increasing the lodging rate significantly.
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    Variation of carbon partitioning in newly expanded maize leaves and plant adaptive growth under extended darkness
    LIANG Xiao-gui, SHEN Si, GAO Zhen, ZHANG Li, ZHAO Xue, ZHOU Shun-li
    2021, 20 (9): 2360-2371.   DOI: 10.1016/S2095-3119(20)63351-2
    Abstract117)      PDF in ScienceDirect      
    Plants must maintain a balance between their carbon (C) supply and utilization during the day–night cycle for continuous growth since C starvation often causes irreversible damage to crop production.  It is not well known how C fixation and allocation in the leaves of crops such as maize adapt to sudden environmental changes.  Here, to quantify primary C fixation and partitioning in photosynthetic maize leaves under extended darkness and to relate these factors to plant growth, maize seedlings were subjected to extended darkness (ED) for three successive days at the 6th leaf fully expanded stage (V6).  ED reduced plant growth and leaf chlorophyll levels but not the rate of net CO2 exchange.  As a result of the reduction in photoassimilates, the accumulation of starch and total soluble carbohydrates (TSC) in mature leaves also decreased under ED.  However, the percentage of the daily C fixation reserved in mature leaves increased.  These transient C pools were largely composed of TSC and were mainly used for consumption by increased nocturnal respiration rather than for transport.  As the days went on, both the amount of C accumulated and the percentage of the daily fixed C that was reserved in leaves decreased, which could be largely accounted for by the attenuated starch synthesis in all treatments.  The activities of ADP-glucose pyrophosphorylase and soluble starch synthase decreased significantly over time.  Therefore, this study concluded that both starch and TSC are involved in the coordination of the C supply and plant growth under a sudden C shortage but that they may be involved in different ways.  While the ratio of reserved C to daily fixed C increased to maintain blade function under acute C starvation, both the amount and the proportion of C reserved in mature leaves decreased as plant growth continued in order to meet the growth demands of the plant.
     
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    Does nitrogen application rate affect the moisture content of corn grains?
    ZHANG Yuan-meng, XUE Jun, ZHAI Juan, ZHANG Guo-qiang, ZHANG Wan-xu, WANG Ke-ru, MING Bo, HOU Peng, XIE Rui-zhi, LIU Chao-wei, LI Shao-kun
    2021, 20 (10): 2627-2638.   DOI: 10.1016/S2095-3119(20)63401-3
    Abstract71)      PDF in ScienceDirect      
    Nitrogen fertilizer application is an important measure to obtain high and stable corn yield, and the moisture content of corn grains is an important factor affecting the quality of mechanical grain harvesting.  In this study, four different nitrogen fertilizer treatments from 0 to 450 kg ha–1 pure nitrogen were set for a planting density of 12.0×104 plants ha–1 in 2017 and 2018, and 18 different nitrogen fertilizer treatments from 0 to 765 kg ha–1 pure nitrogen were set for planting densities of 7.5×104 and 12.0×104 plants ha–1 in 2019, to investigate the effect of nitrogen application rate on the moisture content of corn grains.  Under each treatment, the growth of corn, leaf area index (LAI) of green leaves, grain moisture content, and grain dehydration rate were measured.  The results showed that, as nitrogen application increased from 0 to 765 kg ha–1, the silking stage was delayed by about 1 day, the maturity stage was delayed by about 1–2 days, and the number of physiologically mature green leaves and LAI increased.  At and after physiological maturity, the extreme difference in grain moisture content between different nitrogen application rates was 1.9–4.0%.  As the amount of nitrogen application increased, the corn grain dehydration rate after physiological maturity decreased, but it did not reach statistical significance between nitrogen application rate and grain dehydration rate.  No significant correlation was observed between LAI at physiological maturity and grain dehydration rate after physiological maturity.  In short, nitrogen application affected the grain moisture content of corn at and after physiological maturity, however, the difference in grain moisture content among different nitrogen application rates was small.  These results suggest that the effect of nitrogen application on the moisture content of corn grains should not be considered in agricultural production.
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    Drip irrigation incorporating water conservation measures: Effects on soil water–nitrogen utilization, root traits and grain production of spring maize in semi-arid areas
    WU Yang, BIAN Shao-feng, LIU Zhi-ming, WANG Li-chun, WANG Yong-jun, XU Wen-hua, ZHOU Yu
    2021, 20 (12): 3127-3142.   DOI: 10.1016/S2095-3119(20)63314-7
    Abstract204)      PDF in ScienceDirect      
    The Northeast Plain is the largest maize production area in China, and drip irrigation has recently been proposed to cope with the effects of frequent droughts and to improve water use efficiency (WUE).  In order to develop an efficient and environmentally friendly irrigation system, drip irrigation experiments were conducted in 2016–2018 incorporating different soil water conservation measures as follows: (1) drip irrigation under plastic film mulch (PI), (2) drip irrigation under biodegradable film mulch (BI), (3) drip irrigation incorporating straw returning (SI), and (4) drip irrigation with the tape buried at a shallow soil depth (OI); with furrow irrigation (FI) used as the control.  The results showed that PI and BI gave the highest maize yield, as well as the highest WUE and nitrogen use efficiency (NUE) because of the higher root length density (RLD) and better heat conditions during the vegetative stage.  But compared with BI, PI consumed more soil water in the 20–60 and 60–100 cm soil layers, and accelerated the progress of root and leaf senescence due to a larger root system in the top 0–20 cm soil layer and a higher soil temperature during the reproductive stage.  SI was effective in improving soil water and nitrate contents, and promoted RLD in deeper soil layers, thereby maintaining higher physiological activity during the reproductive stage.  FI resulted in higher nitrate levels in the deep 60–100 cm soil layer, which increased the risk of nitrogen losses by leaching compared with the drip irrigation treatments.  RLD in the 0–20 cm soil layer was highly positively correlated with yield, WUE and NUE (P<0.001), but it was negatively correlated with root nitrogen use efficiency (NRE) (P<0.05), and the correlation was weaker in deeper soil layers.  We concluded that BI had advantages in water–nitrogen utilization and yield stability response to drought stress, and thus is recommended for environmentally friendly and sustainable maize production in Northeast China.
     
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    Maize grain yield and water use efficiency in relation to climatic factors and plant population in northern China
    LIU Yue-e, HOU Peng, HUANG Gui-rong, ZHONG Xiu-li, LI Hao-ru, ZHAO Jiu-ran, LI Shao-kun, MEI Xu-rong
    2021, 20 (12): 3156-3169.   DOI: 10.1016/S2095-3119(20)63428-1
    Abstract174)      PDF in ScienceDirect      
    Water scarcity has become a limiting factor for increasing crop production.  Finding ways to improve water use efficiency (WUE) has become an urgent task for Chinese agriculture.  To understand the response of different maize populations to changes in precipitation and the effects of changes in maize populations on WUE, this study conducted maize population experiments using maize hybrids with different plant types (compact and semi compact) and different planting densities at 25 locations across China.  It was found that, as precipitation increased across different locations, maize grain yield first increased and then decreased, while WUE decreased significantly.  Analyzing the relationship between WUE and the main climatic factors, this study found that WUE was significantly and negatively correlated with precipitation (R (daily mean precipitation) and R (accumulated precipitation)) and was positively correlated with temperature (TM (daily mean maximum temperature), TM–m (Tm, daily mean minimum temperature) and GDD (growing degree days)) and solar radiation (Ra (daily mean solar radiation) and Ra (accumulated solar radiation)) over different growth periods.  Significant differences in maize grain yield, WUE and precipitation were found at different planting densities.  The population densities were ranked as follows according to maize grain yield and WUE based on the multi-site experiment data: 60 000 plants ha–1 (P2)>90 000 plants ha–1 (P3)>30 000 plants ha–1 (P1).  Further analysis showed that, as maize population increased, water consumption increased significantly while soil evaporation decreased significantly.  Significant differences were found between the WUE of ZD958 (compact type) and that of LD981 (semi-compact type), as well as among the WUE values at different planting densities.  In addition, choosing the optimum hybrid and planting density increased WUE by 21.70 and 14.92%, respectively, which showed that the hybrid played a more significant role than the planting density in improving WUE.  Therefore, choosing drought-resistant hybrids could be more effective than increasing the planting density to increase maize grain yield and WUE in northern China.  Comprehensive consideration of climatic impacts, drought-resistant hybrids (e.g., ZD958) and planting density (e.g., 60 000 plants ha–1) is an effective way to increase maize grain yield and WUE across different regions of China.
     
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