Table of Content

12 December 2016, Volume 42 Issue 12

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CROP GENETICS & BREEDING·GERMPLASM RESOURCES·MOLECULAR GENETICS

Fine Mapping of Polycyetic Gene (Bjmc2) in Brassica juncea L.

WANG Gang,ZHANG Xiang-Xiang,XU Ping,LYU Ze-Wen,WEN Jing,YI Bin,MA Chao-Zhi,TU Jin-Xing, FU Ting-Dong,SHEN Jin-Xiong*

Acta Agron Sin. 2016, 42(12):  1735-1742.  doi:10.3724/SP.J.1006.2016.01735

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Multilocular plants have a higher seed yield than bilocular plants in B. juncea, mapping and cloning the multilocular gene(s) might be helpful for rapeseed genetic improvement and explanation of the multilocular trait development mechanism. This study verified backcross populations derived from JD11-2 family different at BjMc2 locus only can be used for BjMc2 mapping. Using AFLP assay and BSA method in BC₅ and BC₆ generations, one AFLP marker linked to the target gene was obtained and converted to SCAR marker (SC1). On the basic of homologous sequences of the AFLP maker in B. rapa, 11 SSR markers and one SCAR marker were identified. Through the screening in theZBjH BAC library of Brassica juncea, two BACs covered the target area were selected and one SSR marker was developed. All the developed SCAR and SSR markers were then used to detect the BC₇ population, and a linkage map for the bilocular gene BjMc2 was built. ZX17 and BACsr96, the closest flanking markers, were mapped at 0.048 cM and 0.340 cM distant from the BjMc2 gene, respectively. Bjmc2 is positioned of 68 kb between 946 kb and 1014 kb in the scaffold000019 physical map of A7 in B. rapa. This result would lay a foundation for cloning polycyetic gene Bjmc2 and selectingpolycyetic lines by marker-assisted selection.

Editing Sites in Transcript of Four F₀-ATPase Subunit Genein Tobacco

TAO Yao, WANG Yu, ZHONG Si-Rong, WU Lin-Min, XIE Li-Juan, NIE Ya-Ping, ZHOU Wei, WANG Jian-Ge, LIU Qi-Yua

Acta Agron Sin. 2016, 42(12):  1743-1753.  doi:10.3724/SP.J.1006.2016.01743

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RNA editing exits extensively in mitochondria of higher plants and is one of the most important post-transcriptional regulation methods of gene expression in mitochondrial genomes of higher plants. At the same time, it is an essential process for forming function proteins. RNA editing can induce mutations in mitochondrial genes including nucleotide insertion, substitution, or deletion, which further affects the splicing and processing of primary transcripts, ultimately resulting in cytoplasmic male sterility (CMS). The results of research using multiple species showed that there is an obvious relationship between the four subunit genesof F₀-ATPase and CMS. To explore the relationship, we studied RNA editing status of four mitochondrial genes atp6, atp9, orf25,and orfB from three tobacco male sterility lines (MS Zhongyan 90, MS Yunyan 85, MS K326) and their corresponding fertile lines . The four mitochondrial genes atp6, atp9, orf25,and orfB and their cDNA were distinctively amplified by PCR from six tobacco lines. After that, by means of making a comparison between the DNA sequences and the cDNA sequences of target genes to find RNA editing sites. The orf25 and orfB gene transcripts had the same RNA editing sites between male sterile and fertile lines. For atp6 gene, RNA editing didn't occur in male sterile lines, while there were six RNA editing sites in fertile lines, which all caused changes in the type of amino acids and there were four editing sites enhancing hydrophobicity of the amino acids. It inferred that the difference of protein's hydrophobicity was most likely to cause CMS. The atp9 gene had ten RNA editing sites in fertile lines, eight of which were the same as those in male sterile lines, while two C→T unique editing sites were absent in male sterile lines, of which one caused changes in amino acid. The nucleotide variations at 223 site of atp9 gene resulted in producing a termination code, which might be the necessary RNA editing to produce normal functional protein. These results suggest that lacking of the unique RNA editing sites might contribute to CMS property in tobacco.

Phenotypic Characterization and Gene Mapping of a Thermo-sensitive AlbinoLeaf Mutant tsa1 in Rice

LIU Yu-Long, LIU Feng, ZHOU Kun-Neng, SU Xiao-Mei, FANG Xian-Wen, ZHANG Yun-Hui, BAO Yi-Qun

Acta Agron Sin. 2016, 42(12):  1754-1763.  doi:10.3724/SP.J.1006.2016.01754

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A thermo-sensitive albino leaf mutant tsa1 was obtained from Ningjing36 induced by Ethyl methane sulfonate (EMS). The mutant developed albinotic leaves under low temperature(20-24°C), and the color of mutant leaves was comparable with the wild-type under high temperature (28-32°C). Compared with wild type, the chlorophyll a and carotene contents of mutant albinotic leaves obviously decreased under low temperature condition. With microscopeobservation, the quantity of normal chloroplast significantly decreased, besides, there were a large number of small abnormal chloroplasts in albinotic leaves. The abnormal chloroplast in albinotic tissue of mutant had no obvious thylakoid stack under transmission electron microscopy. These results indicate that tsa1 mutant has defect on chloroplast development under low temperature. Genetic analysis indicated that the mutant phenotype was controlled by a single recessive nuclear gene. Genetic mapping of the mutant gene was conducted using 368 recessive individuals from F₂ population of tsa1/Nanjing 11, the target gene was finally located in a 163 kb region on the chromosome 5. This study provides a basis for map-based cloning and functional analysis of the target gene.

Mapping QTLs for Wheat Seedling Traits in RILs Population of Yanda 1817 × Beinong 6 under Normal and Salt-Stress Conditions

ZHOU Sheng-Hui,WU Qiu-Hong,XIE Jing-Zhong,CHEN Jiao-Jiao,CHEN Yong-Xing,FU Lin,WANG Guo-Xin,YU Mei-Hua,WANG Zhen-Zhong,ZHANG De-Yun,WANG Ling,WANG Li-Li,ZHANG Yan,LIANG Rong-Qi,HAN Jun

Acta Agron Sin. 2016, 42(12):  1764-1778.  doi:10.3724/SP.J.1006.2016.01764

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Seedling traits are known to be important indicators of salt tolerance inwheat (Triticumaestivum L.). Quantitative trait loci (QTLs) mapping for wheat seedling traits under salt stress and normal hydroponics conditions were conducted at three times during 2013 using a set of 230 recombinant inbred lines (RILs) derived from across of Yanda 1817 × Beinong 6 and an available high-density integrated SSR and SNP genetic linkage map. A total of 69 putative QTLs associated with sevenseedling traits were detected on 20 chromosomes except for 1Aby inclusive composite interval mapping (ICIM) at LOD≥2.5. A single QTL explained 2.70–19.00% of the phenotypic variation. Of which, 46 QTLs showed additive effects originated from Yanda 1817, whereas 23 QTLs showed additive effects derived from Beinong 6, indicating that the founder parentYanda 1817 is an important genetic resource for salt tolerance in wheat. Twelve QTLsare considered to be stable QTLs because they were detected in at least three environments, including the major QTLQTn.cau-7BS.1for tiller numberandthe salt-induced QTL QRn.cau-2Afor root number, bothoriginating from Yanda 1817. These results may explain the genetic bases of luxuriant growing habit and stress tolerance of Yanda 1817.

Cloning and Expression Analysis of a Functional Gene GbVWR Induced by Verticillium dahliae in Gossypium barbadense

ZHANG Li-Jia,ZHANG Yan,RONG Wei,YANG Jun,ZHANG Gui-Yin,WU Li-Qiang,LI Zhi-Kun,WU Jin-Hua,MA Zhi-Ying,WANG Xing-Fen

Acta Agron Sin. 2016, 42(12):  1779-1786.  doi:10.3724/SP.J.1006.2016.01779

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Verticillium dahliae is a destructive, soil-borne fungal pathogen that causes severe losses in cotton yield and fiber quality. Mining functional genes related to resistance against V. dahliae will benefit efforts to genetically improve crop plants. In this study, we identified a gene that involved in cotton defense against V. dahliae based on screening the full-length cDNA library and suppression subtractive hybridization library (SSH) induced by V. dahliae in Gossypium barbadense and Gossypium. hirsutum, respectively. Sequence analysis indicated that there was no any annotation in NCBI database, and we named the sequence from G. barbadense as GbVWR. We characterized GbVWR gene and analyzed its expression. The full length cDNA of GbVWR was 520 bp including a 198 bp open reading frame (ORF), encoding 65 amino acid residues. Bioinformatic analyses suggested that GbVWR belonged to secretory protein and tis theoretical isoelectric point was 5.32. Using pET-32a(+) as a fused expression vector, a recombinant plasmid pET32a-GbVWR was constructed. The recombinant protein was induced in Escherichia coli BL21 (DE3) with 1.0 mmol L^–1 IPTG then GbVWR could express about 7 kD protein in E. coli BL21 (DE3). In addition, diverse cis-acting promoter elements involved in fungal elicitor response, hormone response, wound-response, and flavonoid biosynthetic gene regulation were discovered in the promoter region of GbVWR. qPCR analysis showed that expression level of GbVWR was the highest in roots, and was significantly induced by V. dahliae. Besides, GbVWR could also be induced by SA, ET and GA treatments, respectively. In conclusion, GbVWR is a new functional gene, which involved in multiple signal pathways in cotton defense response to Verticillium wilt.

Transcription Factor SiNF-YA5 from Foxtail Millet (Setaria italica) Conferred Tolerance to High-salt Stress through ABA-independent Pathway in Transgenic Arabidopsis

HUANGSuo,HULi-Qin,XUDong-Bei,LIWei-Wei,XUZhao-Shi,LILian-Cheng,ZHOUYong-Bin,DIAOXian-Min,JIAGuan-Qing,MAYou-Zhi,CHENMing

Acta Agron Sin. 2016, 42(12):  1787-1797.  doi:10.3724/SP.J.1006.2016.01787

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Nuclear transcription factor Y (NF-Y) consisting of three subunits, NF-YA, NF-YB, and NF-YC, plays an essential role in many biologic processes, including growth, development, and abiotic stress response. In this study, a NF-Y like transcription factor gene SiNF-YA5 was isolated from foxtail millet variety Longgu 25. The full-length sequence of SiNF-YA5 gene is 924 bp, encoding 307 amino acids. Molecular weight and isoelectric point of SiNF-YA5 protein are 33.76 kD and 9.19, respectively. There is a conserved CBF domain from the 149th to the 210th amino acids of SiNF-YA5. According to the subcellular localization analysis, SiNF-YA5 was mainly localized and expressed on the plasma membrane and nucleus in plant cell. Gene functional analysis showed that under different NaCl concentration treatments, the germination rate of SiNF-YA5 transgenic Arabidopsis was significantly higher than that of wild-type (WT) Arabidopsis during seed germination stage; root surface area and fresh weight of SiNF-YA5 transgenic Arabidopsis remarkably increased compared with WT during seedling stage. Those results indicated that the overexpression of SiNF-YA5 in transgenic plants could enhance tolerance to high salt. Gene expression analysis showed that the expressions of two salt stress related genes, namely NHX1 and LEA7, increased significantly in SiNF-YA5 transgenic plants. On the other hand, there was no obvious difference in sensitivity to ABA between SiNF-YA5 transgenic Arabidopsis and WT showed during seed germination and seedling stages indicating that SiNF-YA5 could enhance salt tolerance through ABA-independent pathway in transgenic plants.

Codon Optimization and Expression of phyA Gene in Soybean (Glycine max Merr.)

KOU Ying-Ying,SONG Ying-Jin,YANG Shao-Hui*,WANG Jie-Hua

Acta Agron Sin. 2016, 42(12):  1798-1804.  doi:10.3724/SP.J.1006.2016.01798

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Phytic acid is the main anti-nutritional components in the plant origin food. Reducing the phytic acid content of transgenic plants is an effective way to improve the nutrient utilization rate of soybean. In this research, the codons of Aspergillus ficuum phyA were optimized according to the codon usage bias in soybean. The phyA(b) gene with scheming DNA sequence was synthesized chemically, which was suitable for expression in soybean. The plant expression vector pCBPS-phyA(b) was constructed. In the vector, phyA(b) gene was driven by promoter of soybean lectin gene and signal peptide sequence, and transformed into Jilin 35 via Agrobacterium-mediated method. PCR detection indicated that the target gene was successfully integrated into soybean genome. The protein product of bar gene could be detected in all positive plants by LibertyLink strip analysis. Herbicide leaf painting showed that leaves of wild-type plants were lesioned, while there of transgenic plants remained green. In total, 13 phyA transgenic plants and 19 phyA(b) transgenic plants were verified by semi quantitative RT-PCR. The detection results of phytase activity, inorganic phosphorus content and phytic acid content in T3 transgenic soybean seeds, showed that the artificial phyA(b) gene was successfully expressed in soybean, and the phytase activity in phyA(b) gene transforming plants was significantly higher than that in phyA gene transforming plants. It is suggested that codon optimization can significantly improve the expression of foreign genes.

TILLAGE & CULTIVATION·PHYSIOLOGY & BIOCHEMISTRY

Effect of Cutting Roots Vertically at a Place with Different Horizontal Distance from Plant on Yield and Grain Storage Capacity of Summer Maize

XU Zhen-He,LIANG Ming-Lei,LU Du-Xu,LIU Mei,LIU Peng,DONG Shu-Ting, ZHANG Ji-Wang,ZHAO Bin,LI Geng

Acta Agron Sin. 2016, 42(12):  1805-1816.  doi: 10.3724/SP.J.1006.2016.01805

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A field experiment was conducted using two summer maize cultivars, Zhengdan 958 (ZD, shallow root type) and Denghai 661 (DH, deep root type). At the V12 stage, we cut roots vertically at different horizontal distance of 10 cm, 20 cm and 30 cm from maize plant in 60 cm soil depth, with no roots cutting as contrast check, which were referred to as ZDCK, ZD10, ZD20, ZD30 and DHCK, DH10, DH20, DH30 respectively. Roots of ZD10 and ZD20 decreased 24.81%, 11.69% and those of DH10, DH20 decreased 16.82%, 7.52% after cutting roots, respectively. Grain yield of summer maize decreased significantly after cutting roots, with a decrease of 13.09%, 9.10% for ZD10 and ZD20, respectively, and 9.81%, 4.64% for DH10 and DH20. After cutting roots, grains per ear and 1000-grain weight of ZD20, ZD10, DH20, and DH10 declined 4.90%, 5.60%, 4.37%, 7.88%, and 3.38%, 5.15%, 1.15%, 4.97%, respectively, which is the important factors resulting in lower grain yield. Grain sink and setting rate were also decreased to a different extent after cutting roots. Cutting roots decreased days to the maximum grain filling rate (T_max), weight at the time up to the maximum grain filling rate (W_max), maximum grain filling rate (G_max), the phase of active grain filling, and average grain filling rate of two cultivars, with more decrease in Zhengdan 958 than in Denghai661.

Characterization of Populations with Different Yield Levels in Indica Hybrid Rice in Plateau Area of Guizhou Province

LUO De-Qiang,WANG Shao-Hua,JIANG Xue-Hai,LI Gang-Hua,ZHOU Wei-Jia,LI Min,JI Guang-Mei,DING Yan-Feng,LING Qi-Hong,LIU Zheng-Hui

Acta Agron Sin. 2016, 42(12):  1817-1826.  doi: 10.3724/SP.J.1006.2016.01817

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Rice is one of the most important staple food crops in Guizhou province, it is critical to ensure food safety through continually improving grain yield per unit area. In order to study the population quality characteristics of indica hybrid rice with different yield levels in Guizhou plateau mountain area, field experiments were conducted at six planting regions in 2011 and 2012. The populations with super-high-yielding (12.0-14.5 t ha^-1), high-yielding (10.5-12.0 t ha^-1), and medium-yielding levels (9-10.5 t ha^-1) were obtained from super hybrid rice Jinyou785. To study their yield, yield components, and population quality characteristics. Productive panicle number was the most important factor influencing the rice yield across planting regions and years, followed by spikelets per panicle and filled grain percentage. The correlation between yield and grain weight was not significant. Between productive panicle number and yield, the direct path coefficient was 0.5822 in 2011 and 0.7304 in 2012, the correlation coefficient was 0.7771 in 2011 and 0.8858 in 2012. There was little difference in dry matter accumulation at heading among different populations, however, a significant difference in dry matter accumulation at maturity. Compared with high-yielding rice and medium-yielding rice, the averaged dry matter accumulations of super-high-yielding rice were 7.7% and 15.9% higher, respectively. When values were averaged across years, compared with high-yielding rice and medium-yielding rice, the super-high-yielding rice had 9.7% and 21.5% higher ratio of spikelets per leaf area, 10.9% and 17.8% higher ratio of filled grains per leaf area, 4.3% and 8.4% higher grain weight per leaf area, respectively. As for the panicle size, compared with medium-yielding rice, both super-high-yielding and high-yielding rice had more percentage of large panicles with spikelets above 250 and less percentage of panicles with spikelets below 100. As to top four leaves, the medium-yielding rice had the longest 1st leaf and lowest 4th leaf from top, meanwhile, the super-high-yielding and high-yielding rice had the longest 2nd leaf and lowest 4th leaf from top. Therefore, increasing productive panicle number and promoting large panicle formation will be helpful to improve rice yield, in addition, it is also very important to ensure optimum leaf area index at heading and increase the dry matter accumulations after heading stage.

Effects of SA, MeJA, and ACC on Leaf Cuticular Wax Constituents, Structure and Permeability in Brassica napus

LI Shuai,ZHAO Qiu-Ling,PENG Yang,XU Yi,LI Jia-Na,NI Yu*

Acta Agron Sin. 2016, 42(12):  1827-1833.  doi:10.3724/SP.J.1006.2016.01827

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Cuticular waxes are related to plant adaptation to environment stress. In the current study, Brassica napus cv. Zhongshuang 11 grown in the soil treated with adding solutions of SA (200 μmol L^–1), MeJA (100 μmol L^–1), and ACC (200 μmol L^–1) wax, were sampled at the five-leaf stage to clarify the effects of SA, MeJA and ETH on adjusting plant cuticular wax deposition. The leaves were used to analyze the amounts of total cuticular wax and wax constituents, wax crystal structure, and cuticular permeability. The amounts of n-alkanes, secondary alcohols, ketones, aldehydes and total cuticular waxes increased significantly when compared with the control at seven days after MeJA treatment, whereas the amounts of all wax constituents and total cuticular waxes significantly decreased at 14 days after MeJA treatment. The application of SA and ACC had no significant influence on cuticular wax deposition at 7 and 14 days after treatments, except for an amount reduction of primary alcohol, aldehyde and unknown constituents for SA treatment at 14 days after treatment. At 21 days after SA, MeJA, and ACC application, the amounts of total cuticular wax, n-alkanes, ketones and aldehyde significantly increased. C29 n-alkane, C29 ketone, and C30 aldehyde were the main cuticular wax constituents induced by SA, MeJA, and ACC application, implying that n-alkane, ketone and aldehyde might be related to the resistance to stresses induced by these signal molecules. Scan electric microscope analysis indicted that the rod-shape structure of cuticular wax in leaf surface reduced and some rods melted under SA treatment. MeJA and ACC application increased the distribution density of wax crystalloids. The cuticular wax deposition and crystal structure alteration reduced the cuticular permeability and delayed the leaf water loss. The specific increase of C29 n-alkane might be the main reason for reducing leaf water loss in B. napus.

Effects of Supplemental Irrigation at Jointing on Flag Leaf Senescence Characteristics and Grain Yield of Winter Wheat Grown in Two Soil Textures

SONG Zhao-Yun,ZHAO Yang,WANG Dong*,GU Shu-Bo

Acta Agron Sin. 2016, 42(12):  1834-1843.  doi:10.3724/SP.J.1006.2016.01834

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The objective of this study was to understand supplemental irrigation on flag leaf senescence, photosynthetic rate, grain yield, and water use efficiency (WUE) of winter wheat in different soil-texture fields. The experiment was carried out in powder- and sandy-loam plots in the 2013–2014 and 2014–2015 growing seasons. Four irrigation treatments and the zero-irrigation control (D0) were designed to determine the optimal wetting soil depth at jointing stage. Variant amounts of water were supplied at jointing stage for 100% relative water content in 0–10 (D1), 0–20 (D2), 0–30 (D3), and 0–40 cm (D4) soil layers. All irrigation treatments were watered again at anthesis stage for 100% relative water content in the 0–20 cm soil layer. In both powder-loam and sandy-loam plots,the irrigation amount at jointing stage increased obviously with the planed depth of wetting layer, whereas the irrigation amount at anthesis stage varied slightly among treatments. After flowering, the soluble protein content, superoxide dismutase activity, catalase activity, and photosynthetic rate of flag leaves showed an increasing trend in response to the increased irrigation amount at jointing stage, in contrast, the malondialdehyde content in flag leaves had a declined trend. In the powder-loam plot, there was no significant difference between D3 and D4. In the sand-loam plot, there was no significant difference among D2, D3 and D4 treatment. In both soil-texture plots, the deeper soil moisturized at jointing resulted in increased water consumption and grain yield of wheat, and no significant difference was found between D3 and D4. However, WUE in D4 treatment was significantly lower than that in D2 or D3 treatment. Our results suggest that the quantity of supplementary irrigation at jointing stage is determined by soil water condition, and 0–30 cm soil layer with 100% field capacity at jointing stage is the optimal standard under the experimental condition. Besides, keeping 0–20 cm soil layer with 100% field capacity at anthesis by a small amount irrigation is also important. This irrigation regime has the advantages of late senescence, enhanced photosynthesis, and finally increased yield and WUE in both powder-loam and sand-loam fields.

Effects of Light, Nitrogen and Their Interaction on Nitrogen Absorption, Utilization and Matter Production of Maize

SONG Hang,ZHOU Wei-Xia,JIN Ying-Jie,LI Hong-Ping,YANG Yan,YOU Dong-Ling,LI Chao-Hai*

Acta Agron Sin. 2016, 42(12):  1844-1852.  doi:10.3724/SP.J.1006.2016.01844

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A field experiment was conducted using maize cultivar Yuyu 22 with three nitrogen levels (N1: 0 kg ha^-1, N2: 120 kg ha^-1, N3: 240 kg ha^-1) and two light conditions (L1: no shading, L2: shading 14 days from the third day before tasseling) to study the effects of light, nitrogen and their interaction on nitrogen absorption and utilization, matter production of maize in 2012 and 2013. Compared with L1 treatment, L2 not only reduced the activities of nitrate reductase (NR) and glutamine synthetase (GS) in ear leaf and nitrogen accumulation in plant and grain, but also significantly reduced dry matter accumulation and declined the length of ear, kernels per row and kernels per ear, resulting in the final grain yield reduced significantly. However under L2, with increasing nitrogen application level, the activities of NR and GS in ear leaf improved and ear length, kernels per row and kernels per ear increased significantly, the grain yield eventually improved significantly. This indicates that there are significant effects of light, nitrogen and their interaction on matter production , nitrogen absorption and utilization of maize, and that nitrogen fertilizer could partially offset the impact of low-light stress on the matter production and yield of maize.

Effect of Nitrogen on Yield Related Traits and Nitrogen Utilization Efficiency in Zhongmai 175 and Jingdong 17

LIFa-Ji,XUXue-Xin,XIAOYong-Gui,HEZhong-Hu,WANGZhi-Min

Acta Agron Sin. 2016, 42(12):  1853-1863.  doi:10.3724/SP.J.1006.2016.01853

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The objective of this study was to understand the effects of different nitrogen (N) application amounts and split ratios on high efficiency of N uptake and utilization, as well as the response to different N treatments of Zhongmai 175 and Jingdong 17 planted in Wuqiao, Hebei, and Shunyi, Beijing in 2013–2014 and 2014–2015 cropping seasons. Nitrogen fertilizer was applied in different total and split (basal + jointing stage) amounts, namely 0, 60+0, 120+0, 120+60, 120+120, and 120+180 kg ha?1. In the N range of 0–240 kg ha?1 in Wuqiao and 0–180 kg ha?1 in Shunyi, the canopy temperature depression (CTD), normalized difference vegetation index (NDVI), biomass of wheat population, and population spikelets increased with the increase of N application amount, as a result, higher yield at maturity was obtained; however, further more N application had a negative effect, showing decreased thousand-kernel weight (TKW), translocation amount (TA) and efficiency (TE) of dry matter accumulated before flowering to grain, contribution efficiency (CE), harvest index (HI), partial factor productivity from applied N (PFPN), N uptake efficiency (NUpE) and N utilization efficiency (NUtE). Zhongmai 175 had higher yield and yield stability than Jingdong 17 in different N application treatments, showing higher levels of spike number (SN), stability of kernel number per spike (KNS), kernel weight, population vitality, biomass, HI, dry matter accumulation before flowering, TA, and NUpE. These characters might be the physiological basis of high yield and high efficiency in Zhongmai 175. Considering the return from yield and economic benefits, we suggest that the recommended N application amounts for Zhongmai 175 and Jingdong 17 should be 180–240 kg ha?1 in the northern part of Huang–Huai Rivers Valley Wheat Zone and 120–180 kg ha?1 in the Northern Winter Wheat Zone. NDVI and CTD at middle to late grain filling stage can be used for rapid evaluation of varietal sensitivity to nitrogen because they are highly correlated with SN, yield, and biomass of wheat.

RESEARCH NOTES

Effects of Plant Density on Stem Traits and Lodging Resistance of Summer Maize Hybrids with Different Plant Heights

REN Bai-Zhao,LI Li-Li,DONG Shu-Ting,LIU Peng,ZHAO Bin,YANG Jin-Sheng,WANG Ding-Bo,ZHANG Ji-Wang

Acta Agron Sin. 2016, 42(12):  1864-1872.  doi:10.3724/SP.J.1006.2016.01864

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Lodging is an important factor limiting grain yield of summer maize at high plant density. Two summer maize hybrids with different plant heights, namely the short-plant height hybrid Denghai661 (DH661) and the high-plant height hybrid Ludan981 (LD981), were used to study the relationship between stem traits and lodging resistance of summer maize hybrids at 45 000 plants ha^-1, 67 500 plants ha^-1 and 90 000 plants ha^-1. With the increase of plant density, stem diameter and rind penetrometer resistance of summer maize were significantly decreased. Rind penetrometer of 3rd basal node of DH661 at 67 500 plants ha^-1 and 90 000 plants ha^-1 decreased by 8.5% and 22.6%, while those of LD981 decreased by 13.3% and 29.6%, respectively, compared with that at 45 000 plants ha^-1. In addition, with the increase of planting density, the cortex thickness, vascular bundle sheath thickness, and vascular bundle number were significantly decreased, resulting in the increase of lodging rate. However, the extent of variation in these parameters was less for short-plant height hybrid than for high-plant height hybrid, and the yield of short-plant height hybrid was greater than that of high-plant height hybrid, indicating that short-plant height hybrid has better resistance to lodging with high yield at high plant density.