Table of Content

12 April 2022, Volume 48 Issue 4

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REVIEW

Research progress regarding the function and mechanism of rice AP2/ERF transcription factor in stress response

CHEN Yue, SUN Ming-Zhe, JIA Bo-Wei, LENG Yue, SUN Xiao-Li

Acta Agronomica Sinica. 2022, 48(4):  781-790.  doi:10.3724/SP.J.1006.2022.12026

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AP2/ERF (APETALA2/ethylene responsive factor) is a family of plant specific transcription factors that are widely involved in various biological processes including plant growth and development and stress responses. Rice is an important food crop in China, but it is severely affected by multiple adverse environmental factors during growth period. It has been found that AP2/ERF transcription factors play important roles in stress response in rice. In this paper, we reviewed the classification and structure architecture of rice AP2/ERF transcription factors and summarized the function and molecular mechanism of different AP2/ERF subfamilies in rice response to disease, drought, saline, and low temperature stresses. This study provides a reference for further interpretation of the molecular network of rice AP2/ERFs-mediated regulatory network in stress responses and their application potential for stress resistance improvement of rice cultivars.

CROP GENETICS & BREEDING·GERMPLASM RESOURCES·MOLECULAR GENETICS

Fine mapping of yellow-green leaf gene (ygl2) in soybean (Glycine max L.)

WANG Hao-Rang, ZHANG Yong, YU Chun-Miao, DONG Quan-Zhong, LI Wei-Wei, HU Kai-Feng, ZHANG Ming-Ming, XUE Hong, YANG Meng-Ping, SONG Ji-Ling, WANG Lei, YANG Xing-Yong, QIU Li-Juan

Acta Agronomica Sinica. 2022, 48(4):  791-800.  doi:10.3724/SP.J.1006.2022.14062

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Leaf is the main organ of photosynthetic carbon assimilation in soybean, and its color is not only related to the trapping power and conversion efficiency of light energy, but also closely related to the yield of soybean. Therefore, the mining of soybean leaf color-related genes is of great significance to analyze the yield of soybean from the pathway of photosynthetic carbon assimilation. Yellow-green leaf is a mutation type different from common green leaves of soybean, and it is an important genetic material to explore the genes related to leaf color of soybean. In this study, we found a yellow-green leaf mutant ygl2 (yellow-green leaf 2), which was naturally mutated from soybean strain GL11, and its yellow-green leaf phenotype could be stably inherited. Compared with the green leaf wild type GL11, the leaf chlorophyll content of mutant ygl2 decreased significantly, and there were significant differences in plant height, 100-grain weight, and protein content. The segregated population was constructed by GL11 and ygl2. Genetic analysis showed that the yellow-green leaf phenotype of ygl2 was controlled by a pair of recessive nuclear genes. The yellow-green leaf gene ygl2 was located between SSR markers 02_104 and 02_107 at the end of chromosome 2 using the isolated population, with an interval physical distance of 56.1 kb, and contained nine genes. These results laid a solid foundation for map-based cloning and molecular marker-assisted breeding of yellow and green leaf genes in soybean.

Genome editing of BnMLO6 gene by CRISPR/Cas9 for the improvement of disease resistance in Brassica napus L

SHI Yu-Qin, SUN Meng-Dan, CHEN Fan, CHENG Hong-Tao, HU Xue-Zhi, FU Li, HU Qiong, MEI De-Sheng, LI Chao

Acta Agronomica Sinica. 2022, 48(4):  801-811.  doi:10.3724/SP.J.1006.2022.14077

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Gene editing technology can modify the target gene efficiently and accurately, which opens up a new way for crop genetic improvement. Mildew resistance locus O (MLO) gene is a key negative regulator of plant defense against powdery mildew. Mutation of MLO gene can enhance plant resistance to powdery mildew, but whether it has the same function is not reported in oilseed rape. In this study, the relative expression analysis suggested that BnMLO6 gene was induced by Sclerotinia sclerotiorum. To explore the potential role of BnMLO6 gene in pathogen resistance, six homologous copies of BnMLO6 gene mutated synchronously by CRISPR/Cas9 gene editing technology and mlo6-212 mutant line was generated for further analysis. Genetic analysis revealed that CRISPR/Cas9 induced mutagenesis of BnMLO6 gene could be stably inherited. In addition, mlo6-212 mutant line indicated obvious resistance to powdery mildew in both field and greenhouse condition. The lesion area of mlo6-212 mutant was reduced by 19.5% after 24 hours inoculation with S. sclerotiorum. Meanwhile, mutation of BnMLO6 gene could stimulate the spontaneous accumulation of callose in leaves and activate ethylene and jasmonic acid transduction pathway. Thus, BnMLO6 gene was probably involved in multiple pathogen resistance pathways to negatively regulate resistance to powdery mildew and S. sclerotiorum in oilseed rape. The results not only provide theoretical basis for the study of BnMLO6 involved resistance regulation of multiple pathogens, but also provide resistant resources and technical support for genetic improvement of disease resistance in oilseed rape.

Function analysis of GmELF3s in regulating soybean flowering time and circadian rhythm

XU Xin, QIN Chao, ZHAO Tao, LIU Bin, LI Hong-Yu, LIU Jun

Acta Agronomica Sinica. 2022, 48(4):  812-824.  doi:10.3724/SP.J.1006.2022.14076

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Soybean is a typical short-day crop. Photoperiod sensitivity seriously affects flowering time, yield, and planting range of soybean, but the mechanism underlying photoperiod and circadian rhythm regulation is still unclear. In Arabidopsis thaliana, ELF3, together with ELF4 and LUX, forms the ELF4-ELF3-LUX complex (Evening Complex, EC), which plays an important role in circadian rhythm and flowering time regulation. In this study, soybean mutants of Gmelf3a/j, Gmelf3b-1, and Gmelf3b-2 were obtained by CRISPR/Cas9 gene editing system. We found that GmELF3b-1 regulated the flowering time in soybean under long-day conditions by observing flowering phenotypes in these mutants. The phenotypes of heterozygous double mutants revealed that there was functional redundancy among GmELF3a/J, GmELF3b-1, and GmELF3b-2 in regulating flowering time of soybean. Through detecting the expression of circadian related genes in soybean by using qRT-PCR, it was found that the relative expression patterns of GmCAB, GmPRR9a, and GmPRR7a were changed in soybean. In summary, these results suggested that GmELF3a/J, GmELF3b-1, and GmELF3b-2 may regulate the circadian rhythm and flowering time through GmPRR9a and GmPRR7a in soybean.

Identification of sugar transporter gene family SiSTPs in foxtail millet and its participation in stress response

JIN Min-Shan, QU Rui-Fang, LI Hong-Ying, HAN Yan-Qing, MA Fang-Fang, HAN Yuan-Huai, XING Guo-Fang

Acta Agronomica Sinica. 2022, 48(4):  825-839.  doi:10.3724/SP.J.1006.2022.14080

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Sugar transporter proteins (STPs), a class of monosaccharide transporters that mainly transport hexose, play an important role in the growth, development, and stress resistance of crops. Foxtail millet is the main cultivated crop in green dryland agriculture, and also is the model plant for C₄ photosynthesis mechanism and stress resistance gene mining of Gramineae crops. However, no systematical study of SiSTPs gene has been performed in foxtail millet. In this study, we identified the whole genome of six Gramineae crops including foxtail millet by bioinformatics method, and focused on the physicochemical properties, the chromosomal localization, the systematic evolution, gene structure, and the conserved domain. Moreover, the relative expression level of SiSTPs gene and its resistance to the infection of Sclerospora graminicola under drought stress and low phosphate stress in foxtail millet were investigated. The results showed that a total of 24, 26, 23, 22, 33, and 27 STP gene family members were individually identified in Setaria italica, Setaria viridis, Sorghum bicolor, Zea mays, Triticum aestivum, and Oryza sativa, which were divided into four clades by phylogenetic analysis. The 24 SiSTP genes were distributed unevenly on 7 chromosomes, and the size of the encoded amino acids ranged from 499 aa to 581 aa. The SiSTP all had the Sugar_tr (PF00083) conserved domain. The cis-acting elements included a large number of light-responsive elements and stress-responsive elements. These SiSTPs was subjected to strong purification and selection pressure during the evolutionary process of foxtail millet, and had obvious tissue expression specificity and photoinduced phenomena. Different SiSTPs showed different temporal and spatial expression and response to the drought stress, the low phosphate stress, and Sclerospora graminicola infection. Our results provide a theoretical basis for elucidating the function and response mechanism to stress of SiSTP.

Cloning and functional analysis of BnMAPK2 gene in Brassica napus

YUAN Da-Shuang, DENG Wan-Yu, WANG Zhen, PENG Qian, ZHANG Xiao-Li, YAO Meng-Nan, MIAO Wen-Jie, ZHU Dong-Ming, LI Jia-Na, LIANG Ying

Acta Agronomica Sinica. 2022, 48(4):  840-850.  doi:10.3724/SP.J.1006.2022.14061

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The mitogen-activated protein kinase (MAPK) cascade is involved in plant growth and development and it is in response to a variety of biotic and abiotic stresses. In this study, a BnMAPK2 (BnaC01g28210D) gene was isolated and cloned from Brassica napus. The cDNA and its coding sequence were 1516 bp and 1113 bp in length, respectively, encoding 371 amino acids. Bioinformatics analysis revealed that the molecular weight of BnMAPK2 protein was 42,497.0 kD, the isoelectric point was 6.36, protein instability coefficient was 38.74, it was a hydrophobic protein, and it had STKc_TEY_MAPK_ plant (cd07858) conserved structure domain unique to MAPKs protein, protein secondary level. The alpha helix accounted for the largest proportion of 44.05% in the secondary structure of protein, and there was no signal peptide, which was more closely related to the C group AtMAPK2 of Arabidopsis. The core element prediction indicated that BnMAPK2-P contained related cis-acting elements in response to salicylic acid hormone, heat stress, and light, including TCA-element, HSE, AAAC-motif, and MYB binding sites. Real-time quantitative PCR (qRT-PCR) demonstrated that BnMAPK2 was expressed in various tissues and organs in Brassica napus, which was induced by methyl jasmonate, salicylic acid, H₂O₂, injury, high temperature, and Sclerotinia sclerotiorum. The phenotypic data of transgenic Arabidopsis lines expressing BnMAPK2 heterologously showed that compared with the wild type, the overexpression of BnMAPK2 made the bolting period of Arabidopsis plants earlier, and significantly increased plant height, the effective length of main inflorescence, and the number of siliques. We speculated that BnMAPK2 gene was involved in the regulation of plant growth and development. This study provides reference materials and data support for in-depth exploration of the molecular mechanism of BnMAPK2 regulating the growth and development in Brassica napus.

Overexpression of ZmCIPKHT enhances heat tolerance in plant

XU Jing, GAO Jing-Yang, LI Cheng-Cheng, SONG Yun-Xia, DONG Chao-Pei, WANG Zhao, LI Yun-Meng, LUAN Yi-Fan, CHEN Jia-Fa, ZHOU Zi-Jian, WU Jian-Yu

Acta Agronomica Sinica. 2022, 48(4):  851-859.  doi:10.3724/SP.J.1006.2022.13013

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The effects of high temperature stress on the normal growth and yield of plants is more and more serious. To adapt the changes of external environment, plants have evolved a series of molecular genetic mechanisms to respond to high temperature stress. The calcineurin B-like protein (CBL) interacting protein kinase (CIPK) is actively involved in response to high temperature stress depended on ABA signal transduction pathway in plants. Based on previous genome-wide association analysis, a candidate gene ZmCIPKHT related to maize high temperature tolerance was cloned in this study. Real-time quantitative PCR results showed that ZmCIPKHT gene was significantly induced by high temperature stress. Transient transformation of maize protoplasts revealed that ZmCIPKHT was localized in the nucleus. Overexpressing ZmCIPKHT plants of transgenic Arabidopsis thaliana had significantly higher survival rate and better growth status than wild type under high temperature stress. The yeast two-hybrid experiment confirmed that the interaction between ZmCIPKHT protein and ZmCBL4 protein in maize CBLs family. The relative expression levels of genes related to abscisic acid (ABA) pathway in transgenic Arabidopsis thaliana with ZmCIPKHT under high temperature stress were changed accordingly, indicating that the regulations of ZmCIPKHT genes under high temperature stress were in the ABA-dependent pathway. These results provide a new experimental basis for elucidating the molecular mechanism of maize CBL-CIPK signaling pathway dependent on ABA pathway to abiotic stress in plants.

Effects of arbuscular mycorrhizal fungi on sugarcane growth and nutrient- related gene co-expression network under different fertilization levels

KONG Chui-Bao, PANG Zi-Qin, ZHANG Cai-Fang, LIU Qiang, HU Chao-Hua, XIAO Yi-Jie, YUAN Zhao-Nian

Acta Agronomica Sinica. 2022, 48(4):  860-872.  doi:10.3724/SP.J.1006.2022.14052

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Sugarcane is one of the important sugar crops in China. Arbuscular mycorrhizas (AM) fungi are widely distributed. Researches have shown that AM fungi infecting plant roots can promote nutrient absorption and growth of plants. In this study, pot experiment was used to set up with two fertilization levels of conventional fertilization (N) and reduced fertilization (R), and inoculated (AM) and control (CK). There were four treatments in total, and four replicates were set in each treatment. The results revealed that the plants inoculated with AM fungi did not only significantly increased the biomass accumulation, but also significantly affected the pH value, alkali hydrolyzable nitrogen and available phosphorus of sugarcane rhizosphere soil. The biomass accumulation in the AM fungus inoculation treatment under reduced fertilization was significantly higher than that of conventional fertilization. The turquoise module and darkgreen module with high specificity with nutrient phenotypes such as nitrogen and phosphorus were screened by weighted gene co-expression network analysis (WGCNA). The core genes of the module were screened with KME value greater than 0.7 as the threshold, and 408 and 21 core genes were screened, respectively. GO enrichment indicated that these core genes were mainly involved in nutrient transport, metabolism, and enzyme catalysis pathways. Based on annotation information and the connectivity of genes, 28 core genes related to the absorption and transportation of nutrients such as nitrogen and phosphorus and 108 related candidate genes were detected among the core genes screened. This study reveals the effects of AM fungi on sugarcane nutrient absorption, and provides a theoretical basis for further understanding of the molecular mechanisms of AM fungi affecting sugarcane nutrient absorption.

Identification and analysis of RNA editing sites of chloroplast genes in foxtail millet [Setaria italica (L.) P. Beauv.]

DU Xiao-Fen, WANG Zhi-Lan, HAN Kang-Ni, LIAN Shi-Chao, LI Yu-Xin, ZHANG Lin-Yi, WANG Jun

Acta Agronomica Sinica. 2022, 48(4):  873-885.  doi:10.3724/SP.J.1006.2022.14043

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RNA editing is one of the post-transcriptional regulation mechanisms of gene expression in the chloroplast genomes of higher plants, which affects the chloroplast development and leads to albino phenotype or yellow phenotype of plant leaves. In this study, chlorophyll content was measured with a UV spectrophotometer at seeding stage among Changnong 35, E752, and E1005, and chloroplast structure of leaves was observed with a transmission electron microscopy; the online tool Prep-CP was used to predict the RNA editing sites of chloroplast genes; RNA editing site was verified by PCR, RT-PCR, and sequencing method, and the editing sites were compared and analyzed between foxtail millet and other monocotyledon. Furthermore, the relative expression patterns of rpoB and PEP-transcription-dependent photosynthetic pathway related genes (ndhG, psaA, psbA, and rbcL) were analyzed by qRT-PCR at different developmental stages, and the secondary structure of rpoB protein before and after editing was analyzed by bioinformatics. The results showed that chlorophyll content of E752 and E1005 were significantly lower and their chloroplasts were abnormal compared with Changnong 35. A total of 20 RNA editing sites of 10 chloroplast genes were identified, among which all were C to U conversion; the number of editing sites among chloroplast genes was varied, and ndhB had the most editing sites with the number of 6. Among the 20 editing sites, 19 editing sites were highly conserved in the evolution of species, however rpoC1-2753 was a unique editing site in foxtail millet. The editing efficiency of rpoB-467, rpoB-545, and rpoB-560 was distinctly different from those of the other editing sites among Changnong 35, E752, and E1005, leading to the expression level change of ropB, which might further affect the expression levels changes of ndhG, psaA, psbA, and rbcL. Bioinformatics analysis revealed that secondary structure of rpoB protein was changed due to the RNA editing of rpoB-467 and rpoB-560. Our results laid a foundation for the molecular mechanism analysis of chloroplast RNA editing in chloroplast development of foxtail millet.

Genetic analysis and molecular characterization of dwarf mutant gad39 in maize

LIU Lei, ZHAN Wei-Min, DING Wu-Si, LIU Tong, CUI Lian-Hua, JIANG Liang-Liang, ZHANG Yan-Pei, YANG Jian-Ping

Acta Agronomica Sinica. 2022, 48(4):  886-895.  doi:10.3724/SP.J.1006.2022.13026

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Plant height is one of the important selection characters in maize breeding, which determines planting density and lodging resistance, and further affects yield and quality. Therefore, it is of great significance to study the genetic and molecular mechanism of related genes controlling plant height in maize. We performed phenotypic identification, cytological observation, genetic analysis, gene mapping, and gibberellin (GA₃) treatment of dwarf mutant gad39, which is derived from maize inbred line Mo17. At silking stage, the plant height of gad39 was only 100.00 cm, significantly shorter than 192.60 cm of wild type Mo17, resulting in a decrease of 48.08%. Morphological identification showed that tassel length, internode number, and cell size of gad39 mutant were significantly reduced, which might be the main cause of gad39 dwarfism. In addition to plant dwarfness of gad39, the number of tillers increased, ear position decreased, stem became thinner, leaf length became shorter and ear length became shorter. Genetic analysis showed that a single recessive nuclear gene regulated the gad39 mutant phenotype, and gene controlling dwarf trait was mapped between markers td4 and td6 on the long arm of chromosome 3. The physical distance between the two markers was 15.34 kb, which contained a dwarf gene D1/ZmGA3ox2. Sequence analysis also revealed that D1 allele gene in gad39 had 10 InDels and 21 SNPs, resulting in the variations of four amino acids in exons. Mutation sites of gad39 differed from the previously reported sites of mutant dwarf1, d1-4, d1-6016, and d1-3286. In conclusion, gad39 was a novel allelic mutant of D1, which encoded GA3-oxidase (GA3ox), a key enzyme involved in the bioactive GA biosynthesis. The seedling height of gad39 was restored to the level of wild types by GA₃ treatment. In this study, we detected a new dwarfing allelic mutant, which laid a foundation for further analyzing the genetic mechanism of plant height in maize.

Functional analysis of StMAPK4 in response to low temperature stress in potato

FENG Ya, ZHU Xi, LUO Hong-Yu, LI Shi-Gui, ZHANG Ning, SI Huai-Jun

Acta Agronomica Sinica. 2022, 48(4):  896-907.  doi:10.3724/SP.J.1006.2022.14036

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Potato is vulnerable to low temperatures resulting in reduced yield production. MAPK gene is widely involved in a variety of environmental stress, and it has been detected to be involved in low temperature regulation. In this present study, to explore StMAPK4 function in response to low temperature stress, potato cultivar ‘Atlantic’ as the experimental material, the expression characteristics of StMAPK4 gene were analyzed in potato root, stem, and leaf at the different time under low temperature (4℃) stress. StMAPK4 gene was analyzed using bioinformatics and its encoded protein subcellular localization was assayed. StMAPK4 overexpression and RNA interference expression vectors were constructed and obtained transgenic potato plants. The activities of superoxide dismutase (SOD) and peroxidase (POD), and the contents of proline (Pro) and malondialdehyde (MDA) in non-transgenic (NT), overexpressed and RNAi interfered transgenic plants were analyzed under 4℃. The results showed that the isoelectric point (pI) of StMAPK4 was 4.97 and it was acidic protein localized in the nucleus and cell membrane. The relative expression levels of StMAPK4 in roots, stems, and leaves significantly increased under low temperature stress. Compared with non-transgenic plants, the activities of SOD and POD and the content of proline in StMAPK4 overexpressed plants were significantly increased, while the content of MDA was significantly decreased. Compared with NT plants, the activities of SOD and POD, and the content of Pro in StMAPK4 overexpression plants were significantly decreased, while the content of MDA was significantly increased. Phenotypic observation revealed that the leaves of non-transgenic and RNAi interfered expression plants wilted seriously, while the leaves of overexpressed plants were less affected. In summary, the overexpression of StMAPK4 gene can enhance the tolerance of low temperature stress in potato plants.

Development of DNA molecular ID card in hog millet germplasm based on high motif SSR

CHEN Xiao-Hong, LIN Yuan-Xiang, WANG Qian, DING Min, WANG Hai-Gang, CHEN Ling, GAO Zhi-Jun, WANG Rui-Yun, QIAO Zhi-Jun

Acta Agronomica Sinica. 2022, 48(4):  908-919.  doi:10.3724/SP.J.1006.2022.14034

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In order to identify hog millet (Panicum miliaceum) germplasm rapidly, to establish a big data management platform, to provide a theoretical basis for germplasm identification and traceability management, 130 germplasms from four ecological cultivation areas were used as materials to construct a molecular ID based on 35 high-motif SSRs (21, 10, and 4 with four-, five-, and six-nucleotide repeats, respectively). The results showed that 30 out of the 35 SSRs could be used as core markers for the construction of molecular ID cards. Ninety allelic variants were detected; effective allelic variants (Ne) ranged from 2.3186 to 2.9982 with an average of 2.7607; Shannon diversity index (I) ranged from 0.9158 to 1.0873 with an average of 1.0472. The observed heterozygosity (Ho) was 0.5000-0.8678 with a mean of 0.7168; the expected observed heterozygosity (He) was 0.5710-0.6691 with a mean of 0.6386; the Nei’s gene diversity index (Nei) was 0.5687-0.6665 with a mean of 0.6360; the polymorphism information content (PIC) was 0.5151-0.7898, with a mean of 0.6966. All accessions were divided into three groups (Group I, II, and III) according to UPGMA analysis. In terms of Shanxi accessions, landraces and breeding varieties were classified into Group I and III, respectively, and farmers materials were distributed into three groups. Based on PCA analysis, all accessions were classified into four clusters, which were related to their geographical origin. As for the rule that the most germplasms were determined using the least markers, 3 markers were excluded due to their high similarity coefficient with others, namely RYW23, RYW49, and RYW51. Screening the remaining 27 markers, the combinations of 17 SSR (RYW35, RYW40, RYW37, RYW18, RYW30, RYW16, RYW20, RYW19, RYW8, RYW5, RYW3, RYW7, RYW1, RYW14, RYW9, RYW6, and RYW10) could identify all hog millet accessions. The DNA molecular identifications of character strings, bar code, and quick response (QR) codes were constructed via ID analysis 4.0, software online of bar code and QR codes technique (http://barcode.cnaidc.com/app/html/bcgcode128.php and https://cli.im/).

Development and characterization analysis of potato SSR primers and the amplification research in colored potato materials

ZHANG Xia, YU Zhuo, JIN Xing-Hong, YU Xiao-Xia, LI Jing-Wei, LI Jia-Qi

Acta Agronomica Sinica. 2022, 48(4):  920-929.  doi:10.3724/SP.J.1006.2022.14065

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Compared with commonly cultivated potato, colored potato is rich in nutrition, especially in anthocyanins, which is the focus of breeding research in recent years. To date, the number of potato SSR primers developed is limited, especially those related to colored potato. In this study, SSR loci were analyzed using MISA software based on the whole genome. The results were as follows: a total of 218,997 SSR loci were obtained from potato genome with an average of 3.39 kb. Mononucleotide was the main repeat type, accounting for 62.05% of the total SSR, followed by dinucleotide and trinucleotide, accounting for 22.39% and 13.11%, respectively. The repeats of the six nucleotide types ranged from 5 to 746, mainly from 5 to 10, accounting for 60.9% of the total SSRs. A total of 215 motif types were obtained in all detected SSRs. The dominant motifs of the other five nucleotide repeat types were mainly A/T-containing motifs, except for hexanucleotide repeat type. The length of SSR motifs ranged from 12 bp to 20 bp, accounting for 43.19% of all SSRs. A total of 100 SSR primers were designed by Primer 5 software, among which 48 primers were preliminarily screened using parents’ genomic DNA of the colored potato, with an effective amplification rate of 48%. Then, six F₂ individuals were randomly selected for PCR amplification, and 26 primers with clear and stable bands and high polymorphism were finely screened, with the average polymorphism rate of 72.52%. In summary, the number and types of SSR loci in potato genome was abundant and diverse, and the polymorphism was moderate. The developed primers were highly polymorphic, which can be used in the development of SSR markers, genetic diversity analysis, and SSR fingerprint of colored potato, providing a scientific basis for further mining genes related to anthocyanin content.

TILLAGE & CULTIVATION·PHYSIOLOGY & BIOCHEMISTRY

Characteristics of carbon emission and approaches of carbon mitigation and sequestration for carbon neutrality in China’s crop production

YAN Sheng-Ji, DENG Ai-Xing, SHANG Zi-Yin, TANG Zhi-Wei, CHEN Chang-Qing, ZHANG Jun, ZHANG Wei-Jian

Acta Agronomica Sinica. 2022, 48(4):  930-941.  doi:10.3724/SP.J.1006.2022.12073

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Crop production not only ensures national food security, but also is the main source of agricultural carbon emissions and an important pool of carbon sequestration. To clarify the characteristics of carbon emissions from crop production and discuss the approaches to reach the peak and neutrality in major agricultural areas can provide important scientific basis to the decision making of green and high-quality agricultural development and “dual-carbon” goal. Based on the national statistical data, this study compared and analyzed the characteristics of carbon emissions in crop planting regions in China, and presented the recommendations for carbon sequestration and greenhouse gas emission mitigation. The carbon emissions of crop production accounted for 45.5% of the national agricultural total carbon emissions in 2018, and the emissions of farmland methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂) of diesel consumption accounted for 22.9%, 14.7%, and 7.9% of the total carbon emissions of agricultural production, respectively. In terms of the regional emissions, both the total carbon emission of crop production and the carbon emission per sowing area are higher in South than North China, with the highest emissions in East and central China and the greatest potential for emission mitigation. In the carbon emission from crop production, CH₄ emission from rice fields accounts for the main part (50.3%) and is the focus of emission reduction. The annual carbon emission of crop production in China peaked in 2015, and then dropped down. It was mainly attributed to the decrease trend of rice sown area, agricultural nitrogen application rate, and diesel oil consumption. If the existing agricultural imports are not significantly affected, the carbon emissions in crop production have basically reached the peak. However, it is very difficult to achieve carbon neutrality in crop production if only by soil carbon sequestration of farmland, and it is necessary to consider both farmland emission reduction and carbon sequestration. On the premise of high and stable grain yield, the carbon neutrality of modern crop production should prioritize CH₄ and N₂O reduction, and fully exploit the integrated carbon sequestration potential of farmland ecosystems, such as straw utilization, combination of the use and protection of farmland, and construction of farmland forest network.

Effects of close planting densities on assimilate accumulation and yield of soybean with different plant branching types

LI Rui-Dong, YIN Yang-Yang, SONG Wen-Wen, WU Ting-Ting, SUN Shi, HAN Tian-Fu, XU Cai-Long, WU Cun-Xiang, HU Shui-Xiu

Acta Agronomica Sinica. 2022, 48(4):  942-951.  doi:10.3724/SP.J.1006.2022.14045

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To investigate the effects of planting density on leaf area index, dry matter accumulation and distribution, and yield components of different varieties, field experiments were conducted using two soybean varieties with different branching types (Zhongzuo XA12938, a main stem type variety; Zhonghuang 13, a branched type variety) under six planting densities (D1: 13.5×10⁴ plants hm^-2; D2: 18.0×10⁴ plants hm^-2; D3: 22.5×10⁴ plants hm^-2; D4: 27.0×10⁴ plants hm^-2; D5: 31.5×10⁴ plants hm^-2; D6: 36.0×10⁴ plants hm^-2). The results showed that as planting densities increased, soybean LAI reached the highest values (>4) earlier, from 47.0 d and 54.6 d (D1) to 31.0 d and 32.9 d (D6) after seedling emergence for Zhongzuo XA12938 and Zhonghuang 13, respectively. Compared to Zhonghuang 13, the high LAI values in Zhongzuo XA12938 lasted longer and decreased less at the middle and late stages. The degree of increase in dry matter with density varied between treatments. At podding stage, dry weight increased by 77.53% and 51.21% in the high-density treatment (D6) compared to the low-density treatment (D1) for Zhongzuo XA12938 and Zhonghuang 13, respectively. The percentage of dry matter in reproductive organs at maturity stage increased and then decreased with increasing density. The highest yields were achieved under D5 (5000.45 kg hm^-2) treatment and remained stable at increasing densities for Zhongzuo XA12938. The highest yields for both years were achieved under D4 (4477.90 kg hm^-2) and D5 (3935.30 kg hm^-2) treatments for Zhonghuang 13. The average yield of Zhongzuo XA12938 was significantly higher by 22.37% than that of Zhonghuang 13. Grey correlation analysis revealed that plant height and effective pods per unit area were closely related to yield in Zhongzuo XA12938, while effective grains per unit area and height of centre of gravity were more highly correlated with yield in Zhonghuang 13. Zhongzuo XA12938 moderate increase in density can increase the LAI and prolong the duration of its high value, promote dry matter accumulation, increase the proportion of reproductive organs, and improve the yield in soybean. Varieties with strong meristem regulation can be used to improve yields and increase benefits by appropriately increasing planting density in production.

Effects of rice stalks mulching combined with green manure (Astragalus smicus L.) incorporated into soil and reducing nitrogen fertilizer rate on rice yield and soil fertility

WANG Lyu, CUI Yue-Zhen, WU Yu-Hong, HAO Xing-Shun, ZHANG Chun-Hui, WANG Jun-Yi, LIU Yi-Xin, LI Xiao-Gang, QIN Yu-Hang

Acta Agronomica Sinica. 2022, 48(4):  952-961.  doi:10.3724/SP.J.1006.2022.12007

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Planting green manure and straw retention is an effective measure to improve soil fertility. Two-year field experiment were conducted to assess the effects of reduced nitrogen rate under the rice straw mulching combined with planting green manure (Astragalus sinicus L.) at full bloom stage on rice yield, yield components, and soil nutrient availability in Hantai district, Hanzhong city, Shaanxi province from 2018 to 2020. Five treatments were assigned: (1) CK, winter fallow, no straw mulching, no fertilization; (2) NPK, winter fallow, no straw mulching, conventional nitrogen fertilizer rate; (3) GRN1, planting green manure in winter, rice straw mulching with conventional N fertilizer rate; (4) GRN2, planting green manure in winter, rice straw mulching with 80% conventional N rate; (5) GRN3, green manure planting in winter, rice straw mulching with 70% conventional N rate. The results showed that: (I) rice yield (Quanxiangyou 1521) of GRN1 was 10,047 kg hm^-2, which was higher 6.7% than that of NPK, and GRN2 and GRN3 had marginal effects in 2019. Moreover, the yield (Huanghuazhan) of GRN2 and GRN3 were significantly higher than that of NPK by 6.6% and 5.8% in 2020, respectively. Compared with CK and NPK, the rice straw mulching combined with planting green manure significantly enhanced the rice yield by 67.9%-83.0% and 2.8%-6.7%, respectively. (II) Planting green manure combined with rice straw mulching increased soil organic carbon content and available P content in 0-20 soil layer. Compared with NPK treatment, soil organic carbon and available P content of GRN2 increased 6.8%-13.2% and 9.9%-12.6%, respectively. Correlation analysis indicated that rice yield was significantly correlated with plant height, fresh weight per plant, fresh root stubble weight, filled grain number per panicle, and 1000-grain weight. Compared with NPK, GRN2 significantly increased effective panicle, effective grain number per panicle by 13.0%-29.3% and 4.5%-14.3%, respectively. Meanwhile, GRN2 significantly increased plant height, fresh weight per plant, and root fresh weight by 10.4%, 23.6%, and 30.0%, respectively. In conclusion, rice stalks mulching combined planting green manure with 20% reduced nitrogen rate can improve rice yield and agronomic performance, enlarge soil carbon sequestration capacity, and increase soil nutrients availability, which is a green rice cultural practice adapted to Hanzhong area.

Nitrogen accumulation and nitrogen substitution effect of maize under straw returning with continuous cropping

YAN Yu-Ting, SONG Qiu-Lai, YAN Chao, LIU Shuang, ZHANG Yu-Hui, TIAN Jing-Fen, DENG Yu-Xuan, MA Chun-Mei

Acta Agronomica Sinica. 2022, 48(4):  962-974.  doi:10.3724/SP.J.1006.2022.13010

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Crop straw resources in Northeast China are rich, but burning and discarding are serious, and nutrient utilization rate is very low. We explored the feasibility of the substitution of straw returning to nitrogen fertilizer and its effects on nitrogen accumulation under continuous cropping in cold region. A frame culture and continuous positioning experiment was carried out in the experimental site of Northeast Agricultural University from 2017 to 2019, with ¹⁵N labeled urea. A three-factor split-plot design was adopted in this experiment, the main plot was straw returning method with no straw returning (S0) and straw returning (S1), and the sub-plot was nitrogen application levels with 0 (N0), 175 (N1), and 350 (N2) kg hm^-2. Two application methods were set for each fertilizer application amount, one ratio of base fertilizer and top dressing applied was 1:1, and the other ratio of base fertilizer and top dressing applied was 1:0. The results were as follows: When the straw returning amount was 12 t hm^-2, the returning straw could replace 36.8 kg hm^-2 pure nitrogen. The average amount of maize straw was 46.50 million tons in Heilongjiang Province from 2017 to 2019, and straw returning could replace 142,700 tons pure nitrogen. The replace amount of pure nitrogen in the ratio of base fertilizer and top dressing (1:1) was 26.88% higher than that in 1:0. Straw returning was negatively correlated with nitrogen use efficiency in maize. The average nitrogen use efficiency of maize in S0 treatment was 6.09% higher than S1 treatment, and the yield of S1 treatment was 4.66% higher than S0 treatment when the urea application amount was 350 kg hm^-2 (161 kg hm^-2 pure nitrogen). The highest yield of maize was 268.22 g frame^-1 in the treatment of straw returning and topdressing with commonly fertilizer applied in local agriculture. In conclusion, the nitrogen substitution effect was remarkable under maize straw returning in Northeast China. Long-term combined application of crop straw and nitrogen fertilizer significantly improved the biomass, yield, and nitrogen accumulation of maize, which was a cultivation mode for increasing yield and efficiency of maize in Northeast China.

Effects of sowing dates, sowing rates, and nitrogen rates on growth and spectral indices in winter wheat

LI Xin-Ge, GAO Yang, LIU Xiao-Jun, TIAN Yong-Chao, ZHU Yan, CAO Wei-Xing, CAO Qiang

Acta Agronomica Sinica. 2022, 48(4):  975-987.  doi:10.3724/SP.J.1006.2022.11033

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To clarify the effects of sowing dates, sowing rates, and nitrogen rates on growth and spectral indices in winter wheat, a two-year winter wheat field experiment under different sowing dates, sowing rates, and nitrogen rates was conducted. We studied systematically the effects of three factors and their interactions on yield, leaf area index (LAI), and normalized difference red edge (NDRE) of winter wheat at critical growth stages. Furthermore, to facilitate real-time monitoring of winter wheat growth dynamics, we also established the appropriate time-series curves of winter wheat canopy NDRE under different yield levels. The results indicated that the change patterns of NDRE and LAI at critical growth stages were very consistent, and the response of three factors to the two indices at critical growth stages was basically the same in winter wheat. In 2018 and 2019, the yield, LAI, and NDRE of winter wheat at each growth stages decreased with the delay of sowing date. In 2019 and 2020, the yield, peaks of LAI and NDRE under late sowing date were the largest except for the filling stage. The LAI and NDRE of winter wheat at different growth stages in the two years increased with the increase of nitrogen rates. However, there was basically no significant difference among sowing rates. Among the three factors, the sowing dates and nitrogen rates had a significant influence on the time-series curves of winter wheat canopy NDRE. The NDRE time series curves of winter wheat were stretched with the increase of nitrogen rates, the descending part of NDRE time series curve shifted to the left with the delay of the sowing date. In 2018 and 2019, the peak values of NDRE time series curves of winter wheat were declined with the delay of the sowing date. In 2019 and 2020, the peak values of the NDRE time series curves of late sowing and over-late sowing winter wheat were higher than that of suitable sowing wheat. The data of two years were merged to establish suitable time-series curves of winter wheat canopy NDRE under three yield levels, and the yield levels were less than 6.75 t hm^-2, 6.75-8.25 t hm^-2, and higher than 8.25 t hm^-2, respectively. The peak values and width of the NDRE time-series curves increased with the increase of yield level. In summary, winter wheat should be sown early at an appropriate date, but if the accumulated temperature before winter was higher, the sowing date should be postponed appropriately. And the growth of late sowing winter wheat could be improved by increasing a certain amount of sowing rates and nitrogen rates. At the same time, these results could provide a technical support for monitoring the growth of winter wheat under different sowing dates and different yield levels.

Characteristics of panicle stem growth and flowering period of the parents of hybrid rice in machine-transplanted seed production

QIN Qin, TAO You-Feng, HUANG Bang-Chao, LI Hui, GAO Yun-Tian, ZHONG Xiao-Yuan, ZHOU Zhong-Lin, ZHU Li, LEI Xiao-Long, FENG Sheng-Qiang, WANG Xu, REN Wan-Jun

Acta Agronomica Sinica. 2022, 48(4):  988-1004.  doi:10.3724/SP.J.1006.2022.12020

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To study the characteristics of panicle and stem growth and flowering period of restorer line and sterile line under mechanized transplanting mode, and to analyze the reasons for the difficulty of parental flowering period meeting under mechanized transplanting mode Chenghui 727×Shu 21A and Yahui 2115×Yixiang 1A were selected as the materials, and the field experiment was carried out from 2019 to 2020 in this study. Two transplanting methods and seedling ages were determined. Leaf age dynamics, panicle stem growth dynamics, and heading dynamics of restorer line and sterile line were investigated, and the effects of different treatments on the growth and development of panicle, stem and leaf, and flower state of the restorer line and sterile line were statistically analyzed. The results were as follows: (1) The total number of leaves in mechanical transplanting parents decreased by 0.3-0.8 leaves in restorer lines while the sterile line added 0.1-0.4 leaves. Meanwhile, the total number of leaves in restorer lines decreased with the decrease of seedling age, while there was no significant change in the total number of leaves of male sterile lines. (2) The growth process of panicles, stems and leaves of restorer lines in mechanical transplanting was delayed by 2-5 days, while that of sterile lines was delayed by 5-10 days. The panicle differentiation of restorer lines began after jointing, while the panicle differentiation of sterile lines began 5-10 days after jointing. The panicle differentiation duration of restorer lines and sterile lines did not change significantly. The young ear growth curves of all treated parents were well fitted with Logistic curves (R²>0.99). (3) The duration from seeding to heading of machine transplanting parents was longer than that of artificial transplanting parents. The effect of lengthening seedling age was the same as the change of transplanting method and the response of sterile lines to transplanting method and seedling age was more significant than that of restorer lines. (4) The flower encounter index of long seedling age under artificial transplanting in each combination was 100%, and the flower encounter was the best. Flowering encountering index was between 40%-60% of long seedling age under mechanical transplanting and short seedling age under artificial transplanting, followed by flowering status. However, the flowering index of the short seedling age combination of Chenghui 727 × Shu 21A and Yahui 2115 × Yixiang 1A was 0 and 18.18% under mechanical transplanting, respectively, indicating that the absent of flowering date seriously. In conclusion, the growth and development of ear, stem, and leaf of parents were delayed under mechanized transplanting mode, and the prolonged seedling age aggravated the growth and development lag phenomenon of parents. There were some differences in the growth, development, and flowering characteristics between restorer lines and sterile lines under different transplanting methods and seedling ages. The difference in the response of restorer lines and sterile lines to cultivation measures was the main reason for the absence of flowering dates of parents.

Suitable varieties and high-yielding population characteristics of late season rice in the northern margin area of double-cropping rice along the Yangtze River

KE Jian, CHEN Ting-Ting, WU Zhou, ZHU Tie-Zhong, SUN Jie, HE Hai-Bing, YOU Cui-Cui, ZHU De-Quan, WU Li-Quan

Acta Agronomica Sinica. 2022, 48(4):  1005-1016.  doi:10.3724/SP.J.1006.2022.12006

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To clarify the suitable types of rice varieties and the mechanism of high yield formation, we mainly analyzed the yield difference between indica and japonica rice in late season in the northern margin of the double-cropping rice along the Yangtze River. The experiment was conducted from 2018 to 2019 in Lujiang, Anhui province. The differences of yield and yield components, dry matter accumulation, and growth period between indica and japonica rice were compared and analyzed through 17 indica rice and 17 japonica rice varieties (strains) which were cultivated in this local area. The results showed that the overall yield level of japonical rice was similar to that of indica rice. However, compared with indica rice, the japonica rice had the characteristics of fewer yield-limiting factors, superior safety of panicle fullness, higher yield stability, and ecological safety. High-yield japonica rice mainly increased the total dry matter accumulation from transplanting to heading stage so as to improve total spikelets and yield. The effects of dry matter accumulation at different stage with different panicle types on total spikelets were quite different. Among them, the dominance period of dry matter accumulation of medium-large panicle (102.3-112.0 grains per panicle) and small panicle japonica rice (52.0-99.7 grains per panicle) are transplanting to panicle differentiation and panicle differentiation to heading stage respectively and the correlation coefficients with total spikelets were 0.709 and 0.829, respectively. Further analysis revealed that dry matter accumulation during transplanting to panicle differentiation stage of large panicle japonica rice was significantly affected by the number of tillers at tillering stage, while the dry matter accumulation during panicle differentiation to heading stage of small panicle japonica rice was affected by the number of tillers and dry weight of single stem at heading stage. In summary, this study suggested that japonica rice was a suitable late season rice variety in the northern margin area of double-cropping rice along the Yangtze River. The number of spikelets in the high-yielding japonica rice was 33.8×10³-41.0×10³ m^-2, the dry matter accumulation at maturity was 15.2-16.6 t hm^-2, and the daily yield was 58.9-64.3 kg hm^-2 d^-1. Regarding the selection of varieties, high-yield large-panicle japonica rice, such as Jia 58, Wuyujing 6571, and Changyou 5, should have strong tillering ability; while small-panicle rice varieties, such as Ningjing 7, Wuyujing 5745 and Huxiangjing 151, should have a suitable number of tillers at heading stage and dry weight of single stem. In addition, it was necessary to study the optimized cultivation techniques for high-yielding japonica rice varieties with different panicle types in order to further develop the yield potential.

RESEARCH NOTES

Cloning and functional analysis of ScGA20ox1 gibberellin oxidase gene in sugarcane

ZHOU Hui-Wen, QIU Li-Hang, HUANG Xing, LI Qiang, CHEN Rong-Fa, FAN Ye-Geng, LUO Han-Min, YAN Hai-Feng, WENG Meng-Ling, ZHOU Zhong-Feng, WU Jian-Ming

Acta Agronomica Sinica. 2022, 48(4):  1017-1026.  doi:10.3724/SP.J.1006.2022.04274

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GA20-oxidase (GA20ox) is a key rate-limiting enzyme in the synthesis of gibberellic acid (GA), but the biological function and expression pattern of gene GA20ox1 in sugarcane remain unknown. In this study, we cloned GA20-oxidase gene (ScGA20ox1) from the sugarcane variety ROC22 sequence by RT-PCR and RACE, which had a total length of 1574 bp and a complete open reading frame (ORF) of 1125 bp that encoded 375 amino acids. The ScGA20ox1 protein is a hydrophilic protein with a molecular weight of 42.3 kD, an iscelectric point (pI) of 5.95, and no transmembrane structure or signal peptide. Real-time fluorescence quantitative analysis revealed that ScGA20ox1 had the highest expression levels in stems, medium in the leaves, and the lowest in roots of sugarcane seedlings. Drought stress, low temperature stress, and GA₃ treatment change the expression patterns of ScGA20ox1 in different tissues. ScGA20ox1 was transformed into Arabidopsis via Agrobacterium-mediated transformation. Transgenic Arabidopsis thaliana plants with overexpressed ScGA20ox1 were obtained from the transformed Arabidopsis thaliana via Agrobacterium-mediated transformation, which showed a phenotypic variation of plant height and internode length increase. In conclusion, ScGA20ox1 was involved in sugarcane’s growth as a crucial regulator in response to abiotic stress and the phenotypic variation of overexpressed transgenic Arabidopsis thaliana changed, which would lay a theoretical basis for future in-depth studies on ScGA20ox1’s biological function and analysis of the molecular mechanism of sugarcane plant shape regulation.

Creation and identification of peanut germplasm tolerant to triazolopyrimidine herbicides

LIU Jia-Xin, LAN Yu, XU Qian-Yu, LI Hong-Ye, ZHOU Xin-Yu, ZHAO Xuan, GAN Yi, LIU Hong-Bo, ZHENG Yue-Ping, ZHAN Yi-Hua, ZHANG Gang, ZHENG Zhi-Fu

Acta Agronomica Sinica. 2022, 48(4):  1027-1034.  doi:10.3724/SP.J.1006.2022.14066

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At present, the germplasm resources of herbicide-tolerant peanut (Arachis hypogaea) are scarce, which restrict the diversification of peanut-based cropping system. To create peanut germplasm with tolerance to different herbicides, a mutant population consisting of more than 55,000 peanut lines were generated by ethylmethanesulfonate mutagenesis. We screened this population with a variety of different herbicides to obtain multiple mutants with tolerance to different herbicides. One of these lines displayed strong tolerance to florasulam and flumetsulam in the experiments with foliar herbicide spraying under field conditions as well as in various laboratory evaluation for the herbicide tolerance, while the herbicide-tolerant trait did not have adverse effects on peanut yield and quality. To determine whether this trait was associated with a target-site-based resistance to the herbicides, we compared gene sequences and relative expression levels of these two acetohydroxyacid synthases (AHASs) as the herbicide target enzymes between the mutant and wild type. Molecular cloning and sequence analysis revealed that peanut chromosome A10 and B10 each contained a gene, named as AhAHAS1a and AhAHAS1b, which were highly similar to Arabidopsis AHAS. Peanut chromosome A08 and B08 also each carried an AHAS gene, named as AhAHAS2a and AhAHAS2b, respectively. However, compared with the wild type, the genes in the mutants had no nucleotide substitutions that could alter the amino acid sequences. Furthermore, it was evident that there was no significant difference in the relative expression levels of AhAHAS genes between the mutant and wild type. In summary, these results indicate that the herbicide tolerance of the mutant might be caused by non-target-site-based resistance mechanism.