Table of Content

12 October 2020, Volume 46 Issue 10

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REVIEW

Genome dominance and the breeding significance in Triticeae

LIU Deng-Cai, ZHANG Lian-Quan, HAO Ming, HUANG Lin, NING Shun-Zong, YUAN Zhong-Wei, JIANG Bo, YAN Ze-Hong, WU Bi-Hua, ZHENG You-Liang

Acta Agronomica Sinica. 2020, 46(10):  1465-1473.  doi:10.3724/SP.J.1006.2020.01022

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Triticeae tribe houses a number of allopolyploid species that harbor combinations of various genomes. The different genomes of an allopolyploid may have asymmetric contributions to morphological traits. For instance, the taxon traits of allopolyploids within genus Triticum is highly like those from the donor species of A-genome, termed this phenomenon as A-genome dominance. Because of genome dominance, the allopolyploids of Triticeae are grouped into different species clusters with A, D, U, or St as the pivotal (dominant) genome. Genome dominance may confer the advantages in evolution and adaptation. In breeding, it is an important factor to influence the development of novel allopolyploid crops and the design of wheat-alien chromosome translocations.

CROP GENETICS & BREEDING·GERMPLASM RESOURCES·MOLECULAR GENETICS

Mechanism research of Bna-novel-miR311-HSC70-1 module regulating heat stress response in Brassica napus L.

LU Hai-Qin, CHEN Li, CHEN Lei, ZHANG Ying-Chuan, WEN Jing, YI Bin, TU Jing-Xing, FU Ting-Dong, SHEN Jin-Xiong

Acta Agronomica Sinica. 2020, 46(10):  1474-1484.  doi:10.3724/SP.J.1006.2020.04014

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HSP70 (heat shock protein 70) participates in the response to heat stress, and can enhance plant heat tolerance, but there have been no reports of miRNA regulating HSP70 in rapeseed. In this study, a new miRNA, named novel-miR311, was identified in the shoot tip of Brassica napus by high-throughput technology. novel-miR311 was present in Brassica napus but not in Arabidopsis, and 5°-RACE technology confirmed that its two target genes, belonged to heat stress homologous protein gene HSC70-1 (HSP70 family), and could be cleavaged in Brassica napus. An overexpression vector of novel-miR311 was constructed and transformed into Arabidopsis and Brassica napus, and the expression of HSC70-1 in transgenic positive seedlings was decreased significantly. High temperature stress experiments showed that the growth potential and survival rates of Arabidopsis and Brassica napus positive seedlings were lower than those of their corresponding controls. The qPCR results showed that the expression of HSC70-1 gene in rapeseed increased after heat stress than before stress. In conclusion, the results suggest that Bna- novel-miR311 could reduce the heat resistance of Arabidopsis and Brassica napus by mediating cleavaged of HSC70-1.

Functional analysis of Lcye gene involved in the carotenoid synthesis in common wheat

ZHAI Sheng-Nan, GUO Jun, LIU Cheng, LI Hao-Sheng, SONG Jian-Min, LIU Ai-Feng, CAO Xin-You, CHENG Dun-Gong, LI Fa-Ji, HE Zhong-Hu, XIA Xian-Chun, LIU Jian-Jun

Acta Agronomica Sinica. 2020, 46(10):  1485-1495.  doi:10.3724/SP.J.1006.2020.01013

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Yellow pigment in wheat grains, mostly composed of carotenoids, is a main factor for the yellowness of flour and its end-used products. Lycopene epsilon cyclase (LCYE) is a key enzyme for the carotenoid biosynthesis pathway in wheat. Previous studies of Lcye gene mainly focused on QTL mapping, gene cloning, and molecular marker development, but its function and genetic regulatory mechanisms remained unclear. In the present study, in order to further understanding the molecular mechanism of yellow pigment formation in wheat grains, the function and genetic regulation of Lcye were studied by TILLING to screen the EMS-mutagenised population. A total of 21 Lcye mutations including six missense mutations, two synonymous mutations and 13 intron mutations were detected consisted from 2491 M₂ EMS-mutagenised population. The mutation frequency of Lcye in the population was 1/266.1 kb. Two missense mutations (M090815 and M091648) were predicted to have severe effects on LCYE protein function based on PARSENP software. MEME analysis showed that the mutation sites of M090815 and M092230 were located on the conserved domain of Lcye gene. In F₂ populations crossing by six missense mutants and the wild type, C2202T mutation in M090815 significantly reduced yellow pigment content in grains, indicating the mutation played an important effect on LCYE function. The quantitative real-time PCR (qRT-PCR) results also showed that the expression level of Lcye gene were significantly reduced, and the decrease trend of Lcye-B1 and Lcye-D1 expression level was similar during different seed developmental stages, while the expression level of Lcye-A1 exhibited a compensation effect at 14-28 days post anthesis. This study identified Lcye gene function, and provided germplasms and a theoretical basis for the improvement of flour color traits and end-used products.

An integrated high-density SSR genetic linkage map from two F₂ population in Chinese pea

LIU Rong, WANG Fang, FANG Li, YANG Tao, ZHANG Hong-Yan, HUANG Yu-Ning, WANG Dong, JI Yi-Shan, XU Dong-Xu, LI Guan, GUO Rui-Jun, ZONG Xu-Xiao

Acta Agronomica Sinica. 2020, 46(10):  1496-1506.  doi:10.3724/SP.J.1006.2020.04028

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Pea (Pisum sativum L.) is an important food legume crop grown widely throughout the world for humans or livestock consumption. Genetic linkage map constructed with SSR markers have played a vital role in marker-assisted breeding of many crops including pea. Public available and transferable SSR markers and genetic linkage map with sufficient SSR markers based on genetically distinct Chinese pea germplasm are limited despite a long study history on genetic linkage mapping in pea. In this study, in order to obtain more transferable SSR markers and high resolution genetic linkage maps for Chinese pea, 617 polymorphic SSR markers were firstly screened from 12,491 genome-wide SSR markers and some related literatures by our laboratory, and these SSR markers were used to construct an enhanced genetic linkage map for the G0003973 × G0005527 F₂ population. The enhanced genetic linkage map covered 5330.6 cM in total length containing 603 SSR markers with an average inter-marker distance of 8.8 cM, which was significantly improved both in marker number and in density compared with the previous map. 119 polymorphic SSR markers were screened based on the above results to develop a new map for a large W6-22600 × W6-15174 F₂ population including 118 SSR markers with a cumulative length of 1127.1 cM assembled into seven genetic linkage groups. Furthermore, data from the above two genetic maps were combined to build an integrated map of 6592.6 cM, comprising 668 SSR markers, 509 genomic SSRs, 134 EST-SSRs and 25 anchor markers distributed in seven genetic linkage groups. These SSR markers and genetic linkage maps will provide a valuable tool for the genetic study and marker-assisted breeding in pea.

Differential proteomics analysis of fertility transformation of the winter rape thermo-sensitive sterile line PK3-12S (Brassica rapa L.)

MI Wen-Bo, FANG Yuan, LIU Zi-Gang, XU Chun-Mei, LIU Gao-Yang, ZOU Ya, XU Ming-Xia, ZHENG Guo-Qiang, CAO Xiao-Dong, FANG Xin-Ling

Acta Agronomica Sinica. 2020, 46(10):  1507-1516.  doi:10.3724/SP.J.1006.2020.04015

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To reveal the fertility switching mechanism of temperature-sensitive sterility line PK3-12S (Brassica rapa L.), the differentially expressed proteins were isolated and identified using anthers of PK3-12S in sterile/fertile conditions by 2-DE and LC-MS/MS mass spectrometry. The expression level variations of differentially expressed genes were examined by RT-PCR in PK3-12 flower buds during sterility/fertile development. The result showed that the sterile anther size of PK3-12 was small with a little abortive pollen in the anther room under high temperature. The trait of fertility transformation was controlled by a pair of recessive alleles. There were 31 differentially expressed proteins with more than two times of the expression level, including six protein spots with increasing expression, 11 protein spots with reduced expression, 12 protein spots with complete inhibition, and two protein spots with induced expressed. Fifteen differentially expressed proteins involved in the cellular processes such as signal transduction pathways, glyoxylate and dicarboxylate metabolism, glycolysis gluconeogenesis, biosynthesis of secondary metabolites, biontheses of amino acids, chorismate biosynthesis, and carbon metabolism pathways were identified by mass spectrometry. The BrrbcL gene, encoding a Rubisco subunit-binding accessory protein, had an open reading frame (ORF) in length of 1095 bp encoded 364 amino acids. Compared with fertile anthers, the expression level of BrrbcL gene, annexin gene (ANN) and BetVI allergen family gene (BetVI) was significantly down-regulated during sterile anthers development, which indicated that these genes maybe participate in the fertility transformation of the thermo-sensitive sterile line PK3-12S.

QTL detection and stability analysis of rice grain shape and thousand-grain weight based on chromosome segment substitution lines

WANG Xiao-Lei, LI Wei-Xing, ZENG Bo-Hong, SUN Xiao-Tang, OU-YANG Lin-Juan, CHEN Xiao-Rong, HE Hao-Hua, ZHU Chang-Lan

Acta Agronomica Sinica. 2020, 46(10):  1517-1525.  doi:10.3724/SP.J.1006.2020.02008

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Grain shape and 1000-grain weight are the important factors affecting rice yield. Discovering the excellent genes of these traits is of great significance for super high yield rice breeding. In this study, a set of chromosome segment substitute lines (CSSLs), derived from a cross between Koshihikari (a japonica cultivar, as donor patent) and Changhui 121 (an indica restorer line, as a background patent), were used to quantitative trait locus (QTLs) detection and stability analysis in three environments. The results showed that a total of 59 QTLs were identified on chromosomes 1, 2, 3, 4, 5, 6, 7, 10, 11, and 12, respectively, whose contribution rate was 0.77%-36.26%. Among them, 10 pleiotropic QTLs were found, and qGW2-1, qGW2-2, qGW3-1, qGW3-2, qGL3, and qGL12 could all be detected in three environments. Furthermore, qGW3-1 is a novel identified QTL locus. These results lay a foundation for further fine mapping, cloning and marker-assisted breeding of grain shape genes.

Expression profile analysis of low nitrogen stress in Brassica napus

XIAO Yan, YAO Jun-Yue, LIU Dong, SONG Hai-Xing, ZHANG Zhen-Hua

Acta Agronomica Sinica. 2020, 46(10):  1526-1538.  doi:10.3724/SP.J.1006.2020.94197

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The nitrogen fertilizer was overapplied with people’s increased demand for crop yield, but the nitrogen utilization efficiency (NUE) of crops was decreasing. In this study, the differentially expressed genes (DEGs) including the nitrogen absorption, transport, distribution and transcription factors were screened under low nitrogen treatment of 0, 3, and 72 h by the physiological changes and RNA-Seq in rapeseed. The results showed that nitrogen were preferentially allocated to the shoots with the increased glutamine?synthetase (GS) and NUE activities and the decreased nitrate reductase (NR) activity and the total nitrogen concentration under low nitrogen treatment. The analysis of Gene Ontology (GO) enrichment and the Kyoto encyclopedia of genes and genomes (KEGG) metabolic pathway showed that DEGs of the shoots were mainly involved in metabolic process, protein binding, ion binding, and anion binding, while DEGs of the roots were mainly involved in molecular function, primary metabolic process, ion binding, and anion binding. The gene expression profile analysis indicated that after low nitrogen treatment for 72 h, the expression of most genes in BnaGLNs increased; the expression of BnaWRKY33s and BnaWRKY70s showed significantly decreased in roots; the expression of most genes in BnaMYB4s, BnaMYB44s, and BnaMYB51s decreased in the roots; the expression of most genes in BnaNIAs family was up-regulated in roots; and in the subfamily of BnaNRT2.1s and BnaNRT3.1s, the expression of BnaA6NRT2.1 (BnaA06g04560D), BnaA6NRT2.1 (BnaA06g04570D), BnaA2NRT3.1 (BnaA02g11760D), and BnaC2NRT3.1 (BnaC02g16150D) increased significantly in roots. At the same time, skipped exon (SE) and mutually exclusive exons (MXE) type occurred in shoots and roots in order to have a better adaptation under low nitrogen stress. In conclusion, the NUE activity was increased by regulating BnaNRTs, BnaGLNs and BnaNIAs genes, and the BnaMYBs, BnaWRKYs genes and alternative splicing favored Brassica napus to adapt the low nitrogen stress.

Genetic diversity assessment of winter wheat landraces and cultivars in Xinjiang via SNP array analysis

MA Yan-Ming, LOU Hong-Yao, CHEN Zhao-Yan, XIAO Jing, XU Lin, NI Zhong-Fu, LIU Jie

Acta Agronomica Sinica. 2020, 46(10):  1539-1556.  doi:10.3724/SP.J.1006.2020.91077

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Xinjiang is a major wheat production and consumption area in northwest China. Assessment of genetic diversities of wheat landraces and cultivars in Xinjiang has great benefit for wheat cultivar breeding and improvement in this area. In this study, a wheat 55K SNP (single nucleotide polymorphism) chip was employed to perform genome-wide scanning for the genetic diversities of 188 winter wheat varieties from Xinjiang, including 134 landraces and 54 modern cultivars. Our results showed that the polymorphism ratio of the SNP loci was about 95.62% (50,743/53,063). Each chromosome contained 1068-2616 polymorphic loci, and the polymorphic SNP marker number in three genomes was A > B > D. The genetic distance among the 188 wheat varieties ranged from 0.002 to 0.723, with an average of 0.378. The genetic distance of 134 landraces was between 0.002 and 0.400, with an average of 0.070, whereas that of 54 modern cultivars was between 0.004 and 0.337, with an average of 0.114. The genetic distance between landraces and modern cultivars was between 0.605 and 0.723, with an average of 0.699. The clustering results showed that all tested wheat materials could be divided into ten different groups. According to the comprehensive analyses of SNP and pedigree, the genetic diversity was the largest between the cultivars and the landraces, medium between different landraces, and small between modern cultivars. Because the genetic diversity of Xinjiang winter wheat cultivars is not rich enough, the wheat landraces should be used as the breeding materials in the future. Our data provide novel scientific basis and guidance for breeding and improvement of wheat cultivars in Xinjiang.

Selection of candidate genes for chlorophyll content in leaves of Brassica napus using genome-wide association analysis

JIAN Hong-Ju, HUO Qiang, GAO Yu-Min, LI Yang-Yang, XIE Ling, WEI Li-Juan, LIU Lie-Zhao, LU Kun, LI Jia-Na

Acta Agronomica Sinica. 2020, 46(10):  1557-1565.  doi:10.3724/SP.J.1006.2020.04007

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Increasing rapeseed production is important to ensure the national food and oil security. According to the theory of crop source and sink, sufficient photosynthate (sources) is the premise of high yield, and chlorophyll is the important substance for photosynthesis. Therefore, breeding high chlorophyll content Brassica napus is an important way to ensure high yield. In our previous study, 588 excellent germplasm resources collected worldwide were re-sequenced with 5x and 385,692 high-quality SNP markers were obtained. SPAD-502 chlorophyll meter was used to measure the total chlorophyll content of mature leaves in 2018-2019. Genome wide association study (GWAS) was conducted to screen SNP sites significantly related to chlorophyll content. Five SNP loci were identified in 2018, with a contribution rate of 5.51%-7.89%, of which S6_3493805 had the largest contribution. 46 SNP loci were detected in 2019, with a contribution rate of 7.29%-10.34%, of which S13_11413088 had the largest contribution. In total, 2022 rapeseed genes were screened out by comparing the reference genome with genes in the regions of the 500 kb before and after the SNP. Based on the function of Arabidopsis homologous genes previously reported, screened 23 candidate genes, among which five were homologous genes in chlorophyll synthesis pathway. These results lay a foundation for the genetic improvement of chlorophyll content in leaves of B. napus in future.

TILLAGE & CULTIVATION·PHYSIOLOGY & BIOCHEMISTRY

Effects of different sowing dates on crop yield, quality, and annual light-temperature resources utilization for rice-wheat double cropping system in the lower reaches of the Yangtze-Huaihe Rivers valley

CHEN Tian-Ye, YUAN Jia-Qi, LIU Yan-Yang, XU Ke, GUO Bao-Wei, DAI Qi-Gen, HUO Zhong-Yang, ZHANG Hong-Cheng, LI Guo-Hui, WEI Hai-Yan

Acta Agronomica Sinica. 2020, 46(10):  1566-1578.  doi:10.3724/SP.J.1006.2020.02007

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Clarifying the characteristics of the annual light-temperature resources distribution and use efficiency for mechanical transplanted rice-winter wheat double cropping system with high yield and high quality is essential for increasing annual yield and climatic resources use efficiency in the lower reaches of Yangtze-Huaihe Rivers valley. Nanjing 9108 (late-ripen medium japonica rice, LRMJ), Lianjing 11 (medium-ripen medium japonica rice, MRMJ) and Ningmai 13 (winter wheat) were used in the annual field experiment with three different rice sowing date (May 22 (R-I), May 29 (R-II) and June 5 (R-III)) treatments and three different wheat sowing date (November 5 (W-I), November 15 (W-II) and November 25 (W-III)) treatments at Xinghua county of Taizhou city in Jiangsu province. The character of yield, quality formation, annual accumulated temperature, and solar radiation resources distribution were investigated. The results showed that, in rice season, the yield, the amount and production efficiency of the light-temperature resources decreased significantly in Nanjing 9108 with sowing date delayed, whereas the yield and the utilization efficiency of light-temperature resources first reached maximum in R-II treatment and then declined, and the amount of light-temperature resource decreased in Lianjing11. In all sowing date treatments, the yield of Nanjing 9108 (LRMJ) was higher than that of Lianjing 11 (MRMJ). In wheat season, with sowing date delayed, the yield, the amount and production efficiency of light-temperature resources of Ningmai 13 decreased to some extent with the delay of sowing dates. From the perspective of annual production, the annual yield of rice-wheat decreased significantly with the delay of rice-wheat sowing date, and was the highest with combination of R-I for Nanjing 9108 and W-I for Ningmai 13 among all the treatments. The highest ratio of rice yield to annual yield was 62.99%, and the lowest was 55.86%. The highest distribution rate of annual accumulated temperature was 68.38% in rice season and 34.14% in wheat season. The average distribution rate of annual radiation was 51.7% in rice season and 48.3% in wheat season. The downward trend was found in production efficiency of annual accumulated temperature and radiation with the delay of sowing date in rice-wheat season, and the later the sowing date, the more significant the reduction. In terms of quality, with sowing date delayed, the milling quality of Nanjing 9108 (LRMJ) became better and the appearance quality became worse, however, the milling quality of Lianjing11 (MRMJ) became worse and the appearance quality became better. In addition, the cooking and eating quality and nutritional quality of the two varieties (except the taste value of Lianjing 11) became worse. Furthermore, wet gluten content and protein content of Ningmai 13 decreased significantly with sowing date delayed. Therefore, it is an effective approach for promoting the sustainable productivity of mechanical transplanted rice-winter wheat double cropping system by optimizing sowing date and selecting rice varieties with suitable growth durations to achieve high production efficiency of light-temperature resources and annual crop yield in the lower reaches of Yangtze-Huaihe Rivers valley.

Effect of sowing date on daily yield of mechanical indica hybrid rice under different ecological conditions

ZHANG Chi, HE Lian-Hua, LIAO Shuang, GAO Yun-Tian, ZHU Shi-Lin, LI Bo, ZHOU Wei, CHEN Yong, HU Jian-Feng, XIANG Zu-Fen, REN Wan-Jun

Acta Agronomica Sinica. 2020, 46(10):  1579-1590.  doi:10.3724/SP.J.1006.2020.02010

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In order to explore the effect of sowing date on daily yield of mechanical indica hybrid rice under different ecological conditions and put forward the corresponding countermeasures, for high yield, a two-factor split plot design, with three indica hybrid rice (Yixiangyou 2115, F you 498, and Chuanyou 6203) and four sowing dates, was conducted to study the effects of different sowing date and ecological conditions on the whole growth period, grain yield and daily yield of machine-transplanted rice in Nanbu, Shehong, Anzhou, and Dayi of Sichuan province. The results showed that there were differences in the whole growth period, yield and daily yield of rice under different ecological conditions. As the sowing date was postponed from late March to early May, the days from sowing to jointing were shortened and the days from heading to maturity were increased, the average whole growth period was shortened from 159.5 days to 150.7 days, the average yield was decreased from 10,260.45 kg hm ^-2 to 7795.83 kg hm^-2, and the average daily yield was decreased from 64.58 kg hm^-2 d^-1 to 51.95 kg hm^-2 d^-1. The effects of meteorological factors on grain yield and daily yield of machine-transplanted indica hybrid rice were different under different ecological conditions. The yield was significantly positively correlated with the average daily temperature range and sunshine hours of the whole growth period, while yield was significantly negatively correlated with the average daily temperature, average daily minimum temperature, average daily relative humidity and rainfall of the whole growth period of rice. The daily yield was significantly positively correlated with the average daily temperature range and sunshine hours of the whole growth period, while significantly negatively correlated with the average daily minimum temperature and the average daily relative humidity of the whole growth period. For different experimental region, the daily yield was significantly negatively correlated with the average daily temperature in Nanbu, Shehong, and Dayi. In the west plain area and the middle and northeast hilly areas of Sichuan Basin, the preferred varieties should be F you 498, winter idle field or vegetable stubble rice should be sown in late march, while wheat (rapeseed) stubble rice should be sown as early as possible after the previous harvest, and generally sown in late April for higher yield and daily yield.

Comprehensive identification and evaluation of foxtail millet for saline-alkaline tolerance during germination

CHEN Er-Ying, WANG Run-Feng, QIN Ling, YANG Yan-Bing, LI Fei-Fei, ZHANG Hua-Wen, WANG Hai-Lian, LIU Bin, KONG Qing-Hua, GUAN Yan-An

Acta Agronomica Sinica. 2020, 46(10):  1591-1604.  doi:10.3724/SP.J.1006.2020.04064

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In the present study, the evaluation of 53 main foxtail millet cultivars was carried out under saline-alkaline mixed stress (100 mmol L^-1, NaCl : NaHCO₃ = 4 : 1). The results showed that germination potential, germination rate, root length, shoot length, fresh root weight and fresh shoot weight of the 53 cultivars were inhibited, among which with root length most affected by the salt and alkaline condition. Exposed to such a stress condition, significant or extremely significant positive correlations were observed for relative germination potential and relative germination rate, relative root length and relative shoot length, and relative fresh root weight and relative fresh shoot weight. 14 traits were integrated into four principal components with a cumulative contribution rate of 90.4% through principal component analysis (PCA). Composite scores for saline-alkaline tolerance were calculated from membership function with scores of the four principal components. The 53 cultivars were assigned to six different groups of saline-alkaline resistance by using cluster analysis, including 2 highly resistant, 16 moderately resistant, 17 lower resistant, 6 sensitive, 9 susceptible and 3 extremely intolerant foxtail millet cultivars. Meanwhile, a regression equation, D° = 0.298 + 0.037 X₂ + 0.144X₃ + 0.018X₆ + 0.209X₇ - 0.183X₉ + 0.115X₁₁ - 0.201X₁₂ + 0.112X₁₃ - 0.101X₁₄ + 0.284X₁₅, was established to estimate the tolerance of foxtail millet cultivars to saline-alkaline stress. Relative germination rate, salt injury rates for root length and shoot length, and root-shoot ratio could be regarded as the indicators of assessing the resistance of foxtail millet to saline-alkaline mixed stress.

Effects of nitrogen and density interaction on root morphology, plant characteristic and pod yield under single seed precision sowing in peanut

Jun-Hua LIU, Zheng-Feng WU, Pu SHEN, Tian-Yi YU, Yong-Mei ZHENG, Xue-Wu SUN, Lin LI, Dian-Xu CHEN, Cai-Bin WANG, Shu-Bo WAN

Acta Agronomica Sinica. 2020, 46(10):  1605-1616.  doi:10.3724/SP.J.1006.2020.04058

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In order to determine the suitable nitrogen level and planting density for single seed precision sowing of peanut, field comparison experiments were conducted using Huayu 22 with three nitrogen levels at 0 (N0), 60 (N1), 120 (N2) kg hm^-2 and three planting densities at 79,300 (D1), 158,600 (D2), and 237,900 (D3) plants hm^-2 in 2018 and 2019. The effects of nitrogen, density and their interaction on root morphology, plant characteristics and yields of single seed precision sowing peanut were studied by the split plot design for two factors. Nitrogen fertilizer had no significant effect on root length, root surface area, root volume and root dry weight, whereas significant on density. Root length, root surface area, root volume and dry weight per plant decreased with the increase of density, D1 was significantly higher than D2 and D3, but there was no significant difference between D2 and D3 treatments. And root length, root surface area, root volume and dry weight of unit area increased with the increase of density, D1 was significantly lower than D2 and D3, and there was no significant difference between D2 and D3 treatments. The interaction of nitrogen and density had a significant effect on the root length and surface area of unit area in the harvest stage in 2019. Compared with D1, the increase range of D3 in N1 treatment was significantly higher than that of N0 and N2. As to plant characteristics, nitrogen fertilizer and the interaction of nitrogen fertilizer and density were different between years and periods, and with the increase of density, the number of leaves of main stem, the number of lateral branches and the first internode thickness of main stem decreased. The effects of nitrogen fertilizer on pod yield was not significant, whereas pod yield increased with the increase of density. Pod yields were positively correlated with root volume, root dry weight, leaves of main stem, height of main stem and length of lateral branches. In conclusion, considering the yield and benefit comprehensively, the suitable nitrogen fertilizer (N) level is 60 kg hm^-2 and the planting density is 188,000 plants hm^-2.

Effect of tetramethyl glutaric acid on summer maize photosynthesis characteristics

MA Zheng-Bo, DONG Xue-Rui, TANG Hui-Hui, YAN Peng, LU Lin, WANG Qing-Yan, FANG Meng-Ying, WANG Qi, DONG Zhi-Qiang

Acta Agronomica Sinica. 2020, 46(10):  1617-1627.  doi:10.3724/SP.J.1006.2020.03002

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In this study, we explore the effect of tetramethyl glutaric acid (TGA) photosynthesis characteristics and yield in summer maize. Field experiments were conducted in Xinxiang experimental station of Chinese Academy of Agricultural Sciences in 2018 and 2019. Two widely planted maize cultivars were planted, and five TGA application gradients (0, 75, 150, 225, and 300 g hm^-2) were carried out. The results showed that the appropriate TGA treatment could increase maize yield, delay functional leaf senescence rate during the whole growth stage, and enhanced net rate during the grain-filling stage, respectively. The optimal TGA dosage was 150 g hm^-2, the yield of Zhongdan 909 (ZD909) and Jingnongke (JNK728) respectively increased by 8.7% and 11.7% compared to the control treatment in two experimental years under the optimal TGA treatment. Furthermore, chlorophyll content, soluble protein content and leaf area duration of ZD909 and JNK728 increased by 14.3% and 19.7%, 18.7% and 22.7%, 10.9% and 16.9%, respectively, in contrast, leaf senescence rate decreased by 55.9% and 56.5%, respectively during the experimental years. In addition, net photosynthetic increase by 44.0% and 58.4%, respectively, during the grain-filling stage. Correlation analysis indicated maize yield was significantly negatively correlated with leaf senescence rate during the whole growth period, and significantly positively correlated with net photosynthetic rate during grain-filling stage. In conclusion, suitable TGA treatment could delay leaf senescence rate by increasing leaf chlorophyll and soluble protein content, and improve ear leaf net photosynthetic rate during the reproductive growth stage, and ultimately increased maize yield.

RESEARCH NOTES

Promoter cloning and expression analysis of the hexokinase gene CsHXK2 in tea plant (Camellia sinensis)

LI Na-Na, LIU Ying, ZHANG Hao-Jie, WANG Lu, HAO Xin-Yuan, ZHANG Wei-Fu, WANG Yu-Chun, XIONG Fei, YANG Ya-Jun, WANG Xin-Chao

Acta Agronomica Sinica. 2020, 46(10):  1628-1638.  doi:10.3724/SP.J.1006.2020.94166

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Hexokinase is a kind of dual-function protein playing a crucial role in hexose phosphorylation and sugar signaling transduction in plants. In our previous study, four hexokinase genes from tea plant were cloned, and CsHXK2 gene encoded 492 amino acid residues was classified as Type A HXKs together with AtHXK3 from Arabidopsis thaliana and LeHXK4 from tomato. 2029 bp promoter of CsHXK2 gene was obtained by RT-PCR. Further sequence analysis showed that CsHXK2 gene may be regulated by light, low temperature, pathogen, sugars and phytohormones, and specifically expressed in leaves, flowers, seeds, roots, axillary buds. CsHXK2 protein was localized in the chloroplast. Functional complementation of the hexokinase-deficient yeast mutant showed that the CsHXK2 mature protein removal of chloroplast transit peptide, had phosphorylation activity of glucose and fructose. Tissue-specific expression analysis found that CsHXK2 had the highest transcriptional levels in roots and stems, whereas the lowest in old leaves. The expression level of CsHXK2 gene was significantly down-regulated in both cold stress treatment and leaves infected treatment by Colletotrichum camelliae. However, the expression level of CsHXK2 was significantly stimulated after exogenous GA₃ treatment in tea leaves. In conclusion, the results suggested that CsHXK2 played an important role in the regulation of both development and stress responses in tea plant.

Development and application of the marker for imidazolinone-resistant gene in Brassica napus

HU Mao-Long, CHENG Li, GUO Yue, LONG Wei-Hua, GAO Jian-Qin, PU Hui-Ming, ZHANG Jie-Fu, CHEN Song

Acta Agronomica Sinica. 2020, 46(10):  1639-1646.  doi:10.3724/SP.J.1006.2020.04056

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Weed damage is one of the most important factors restricting the development of rapeseed production in China. Cultivation of herbicide-resistant varieties combined with chemical herbicides was an extremely effective help to control field weed in rapeseed production. To accelerate the breeding of cultivars with resistance imidazolinone herbicides through molecular marker-assisted selection in Brassica napus, the simplest, most cost-effective and high-throughput KASP markers were developed by using a SNP mutation at 1913 bp position of ALS (acetolactate synthase) gene in the mutant M9. A polymorphic marker designed KBA1R19681913B was obtained to effectively distinguish the homozygous resistant M9 from susceptible rapeseeds. Meanwhile, the KASP marker was evaluated in two F₂ populations and could effectively discriminate three genotypes. F₂ populations gave a good fit to the expected 1:2:1 ratio, confirming a single gene Mendel model with the perfect matched between phenotyping and genotyping. About more than two hundred homozygous restoring lines containing BnALS1R were developed through KASP marker selection in multi-generation backcross and showed stable imidazolinone herbicide resistance. This functional marker can also be used to identify the purity of hybrid seeds at the seedling stage. In conclusion, the validated KASP marker KBA1R19681913B would provide a technical support for developing herbicide-resistant rapeseed in marker-assisted selection and identification of resistant germplasm.