Table of Content

12 September 2020, Volume 46 Issue 9

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CROP GENETICS & BREEDING·GERMPLASM RESOURCES·MOLECULAR GENETICS

Exploration of specific gene(s) for ear rot resistance to Fusarium verticilloides in maize

WEN Jing, SHEN Yan-Qi, HAN Si-Ping, XING Yue-Xian, ZHANG Ye, WANG Zi-Yu, LI Shi-Jie, YANG Xiao-Hong, HAO Dong-Yun, ZHANG Yan

Acta Agronomica Sinica. 2020, 46(9):  1303-1311.  doi:10.3724/SP.J.1006.2020.03004

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Ear rot in maize, caused by fungal pathogens, poses a grave threat to maize production, and current inbred lines in use generally lack resistance to ear rot. It is essential to explore the resistant loci and corresponding resistance genes for improvement of the resistance to ear rot in maize by molecular marker-assisted breeding and biotechnology breeding. The purpose of this study was to explore the resistance loci of ear rot caused by Fusarium verticilloides and preliminary identify candidate genes by transcriptome analysis and genome-wide association. The result of transcriptome analysis showed that there were 10,761 differentially expressed genes between inbred lines Fa A and Ye 81162 at seven days after artificial inoculation with Fusarium verticilloides. A total of five SNPs significantly associated with ear rot resistance were detected by genome-wide association analysis, and these SNPs were distributed on chromosomes 1 and 9. By comparing B73 RefGen_v3 and annotating, it was found that the genes involved near the SNP site included acyl activating enzyme 1 peroxisome, protein phosphatase 2C 48, magnesium transporter, receptor protein kinase CRINKLY4 and zinc finger CCCH domain protein 19. The zinc finger CCCH domain protein 19 detected in genome-wide association just was the differentially expressed gene from transcriptome analysis, indicating that Zinc finger CCCH domain protein 19 probably is related to resistance to Fusarium verticilloides ear rot in maize. The results not only provide theoretical basis and important genetic resources for resistance gene cloning and molecular breeding of maize, but also lay a foundation for analysing the interaction between maize and pathogen.

Prokaryotic expression, subcellular localization and yeast two-hybrid library screening of BnMAPK1 in B. napus

WANG Zhen, YAO Meng-Nan, ZHANG Xiao-Li, QU Cun-Min, LU Kun, LI Jia-Na, LIANG Ying

Acta Agronomica Sinica. 2020, 46(9):  1312-1321.  doi:10.3724/SP.J.1006.2020.04019

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Plant mitogen-activated protein kinases (MAPKs) cascades are common signal transduction pathways across the membrane in growth process, they are involved in transducing extracellular stimuli to induce a range of cellular responses. To date, little is known about the role of C-group MAPKs in B. napus. In this study, we analyzed biological process ontology of one C-group BnMAPK1 gene in rapeseed, indicating that BnMAPK1 may be involved in protein phosphorylation, auxin-mediated signaling, stress response, cell cycles and transcription. With 369 amino acid residues, the hydrophilic protein of BnMAPK1 could be induced to express one 42.5 kD protein in the prokaryotic system. The subcellular localization of BnMAPK1 mainly focused in the nucleus. The pGBKT7-BnMAPK1 bait plasmid without toxicity and auto-activation was constructed to perform yeast-two hybrid screening. To further study the function and mechanism of BnMAPK1, we extracted the total RNA of roots, stems, and leaves of B. napus (Zhongyou 821) at seedling stage respectively, and isolated and purified the mRNA to construct the mix cDNA library by SMART method. The BnMAPK1-interacting proteins were screened through co-transformation with bait plasmid and cDNA prey library, demonstrating that BnMAPK1 plays an important role in the growth and development processes, abiotic and biotic stresses, transcription, protein synthesis and metabolism, translation, and post-translational modification, and so on. These results provide a new perspective for the research of MAPKs cascades, especially for C-group MAPKs, and lay a theoretical foundation for the stress resistance mechanism research and molecular breeding in rapeseed.

Regulation of flavonoid pathway by BjuB.KAN4 gene in Brassica juncea

GAO Guo-Ying, WU Xiao-Fang, HUANG Wei, ZHOU Ding-Gang, ZHANG Da-Wei, ZHOU Mei-Liang, ZHANG Kai-Xuan, YAN Ming-Li

Acta Agronomica Sinica. 2020, 46(9):  1322-1331.  doi:10.3724/SP.J.1006.2020.04008

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MYB transcription factors KAN4 can effectively regulate the biosynthesis of plant proanthocyanidins. In order to investigate the function of the MYB transcription factor KAN4 on the regulation of proanthocyanidin synthesis in Brassica juncea, we cloned BjuB.KAN4 gene from purple-leaf mustard rape (PM), which encoded 266 amino acids. The BjuB.KAN4 protein contained a highly conserved MYB-like DNA-binding domain belongs to the 1R-MYB transcription factor family. BjuB.KAN4 gene expression showed significantly higher level in root than in leaf and stem. GUS histochemical staining showed that this gene might be expressed in vascular tissues. Overexpression of BjuB.KAN4 in hairy roots of PM and Sichuan Yellow (SY) increased the expression level of some key enzyme genes in the flavonoids biosythesis pathway, such as Bju.CHS and Bju.DFR. The total flavonoids content was 2.798 mg g^-1 in transgenic roots of PM, which was 1.3 times higher than that of the control, and 2.567 mg g^-1 in transgenic roots of SY, which was 1.2 times higher than that of control. In transgenic Arabidopsis plants overexpressing BjuB.KAN4, total flavonoids was 0.237 mg g^-1, which was 1.5 times higher than that of wild type, however, the proanthocyanidins content decreased. This study indicates that the BjuB.KAN4 gene is involved in the regulation of PM flavonoid synthesis, and provides a reference for the research of regulation mechanism of proanthocyanidins synthesis in Brassica.

Molecular identification of rice bacterial blight susceptible gene Xig1 and creation of disease resistant resources

ZHENG Kai-Li, JI Zhi-Yuan, HAO Wei, TANG Yong-Chao, WEI Ye-Na, HU Yun-Gao, ZHAO Kai-Jun, WANG Chun-Lian

Acta Agronomica Sinica. 2020, 46(9):  1332-1339.  doi:10.3724/SP.J.1006.2020.02013

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The rice bacterial blight susceptible gene Xig1 (Xoo-induced-gene 1), was found highly induced by Xanthomonas oryzae pv. oryzae (Xoo) in susceptible parent line IR24 but not in introgression line W6023. In this study, we cloned and sequenced Xig1 alleles isolated from W6023 and IR24, and the main difference in nucleotide sequences between Xig1 alleles of W6023 and IR24 was in the promoter region. Subcellular localization in rice protoplast indicated that XIG1 localized to cytoplasm. CRISPR/Cas9-based genome editing technologies were also applied to knock out Xig1 in IR24. Eight Xig1-edited mutant lines showed a higher resistance to Xoo, and all agronomic traits surveyed are consistent. Xig1 is a novel susceptible gene for bacterial blight in rice. The studying of the mechanism of Xig1 to Xoo in rice will not only provide a theorical guidance for disease resistance resource, but also benefit the understanding of plant innate immunity.

Development and application of InDel markers based on high throughput sequencing in barley

XU Ting-Ting, WANG Qiao-Ling, ZOU Shu-Qiong, DI Jia-Chun, YANG Xin, ZHU Yin, ZHAO Han, YAN Wei

Acta Agronomica Sinica. 2020, 46(9):  1340-1350.  doi:10.3724/SP.J.1006.2020.91076

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Molecular markers are the basic tools in genetic research and widely used in genetic diversity analysis, germplasm identification, genetic map construction and gene mapping. Based on the whole genome re-sequencing data of barley, we developed 118 pairs of InDel markers covering the whole barley genome. Forty-nine barley germplasms from different geographical regions were used to detect the effectiveness of primers. And 72 co-dominant InDel markers with two alleles were selected for further genetic distance analysis in 288 barley germplasm and constructing phylogenetic tree. Thirty-two core InDel markers were screened, covering seven chromosomes of barley, with an average PIC of 0.44, and an average MAF of 0.34. The tested barley germplasms were rich in genetic diversity and could cluster most of the varieties with the same geographical origin. This study indicated that the 32 dimorphic InDel markers developed not only effectively reflect the genetic relationship between varieties, but also enrich the molecular markers used for the identification of barley varieties. The above core InDel markers have provided certain the theoretical significance and application value in on the identification of barley varieties, the relationship analysis of barley resources and group division of barley resources.

Functional analysis of ZmCIPK24-2 gene from maize in response to salt stress

LI Jian, WANG Yi-Ru, ZHANG Ling-Xiao, SUN Ming-Hao, QIN Yang, ZHENG Jun

Acta Agronomica Sinica. 2020, 46(9):  1351-1358.  doi:10.3724/SP.J.1006.2020.03008

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Soil salinity affects the normal growth and development of crops, resulting in reduced crop yields. In the process of long-term adaptation, plants have evolved targeted salt-resistant molecular mechanisms. The calcineurin B-like protein (CBL) and CBL-interaction protein kinase (CIPK) are involved in plant response to salt stress. In this study, we identified an AtSOS2 homologous gene ZmCIPK24-2. The results of real time-qPCR showed that ZmCIPK24-2 gene was ubiquitously expressed in maize, especially in pollen, and was induced by salt stress. It was found that ZmCIPK24-2 could partially complement the salt-sensitive phenotype of the atsos2 mutant. The survival rate and the root length of ZmCIPK24-2-overexpressed lines were significantly increased compared with atsos2 mutant under high salt concentration. Subcellular localization experiments showed that ZmCIPK24-2 was localized in cytoplasm, cell membrane, and nuclear membrane. Yeast two-hybrid experiments and LUC complementation imaging assays showed that ZmCIPK24-2 was interacted with ZmCBL1, ZmCBL4, ZmCBL8, and ZmCBL9, respectively. This study provides a new experimental evidence for the functional analysis of CBL-CIPK signaling pathway in maize.

Phenotype identification and gene mapping of defective kernel 48 mutant (dek48) in maize

SHI Hui-Min, JIANG Cheng-Gong, WANG Hong-Wu, MA Qing, LI Kun, LIU Zhi-Fang, WU Yu-Jin, LI Shu-Qiang, HU Xiao-Jiao, HUANG Chang-Ling

Acta Agronomica Sinica. 2020, 46(9):  1359-1367.  doi:10.3724/SP.J.1006.2020.03005

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Maize kernel is not only a main nutrient storage organ, but also a model organ for seed development research of gramineous plants. In this study, a stable defective kernel mutant 48 (dek48) was identified from a library of mutants of the maize inbred line Zheng58 treated with ethylmethane sulfonate (EMS). Compared with wild type, the hundred-kernel weight of the dek48 was decreased greatly due to shrunken appearance and small flat size. Moreover, the dek48 was incapable of growing into a plantlet owning to the severely defective embryo and endosperm. The obvious defective development of the mutant can be observed at 12 days after pollination (DAP), indicating that the mutation occurred at an early stage of kernel development. Microscopic observation by scanning electron microscopy (SEM) revealed that starch granule of the dek48 was significantly smaller than wild type (WT). The observation of the paraffin section demonstrated that the starch granule of dek48 endosperm was partially filled and the aleurone layer cells developed irregularly. Genetic analysis based on kernel form indicated that the mutant trait was controlled by a single recessive gene. Based on genetic F₂ population mapping, the gene of the mutant was located between 7.39 Mb-7.52 Mb on chromosome 3. The bioinformation analysis indicated that there were six new open reading frames (ORFs) and unknow genes related to kernel development in this region. Furthermore, candidate gene will be identified through sequencing and gene expression analysis in the future.

Mechanism of GhPIF4 regulating anther abortion under high temperature stress in cotton

CHEN Miao, XIE Sai, WANG Chao-Zhi, LI Yan-Long, ZHANG Xian-Long, MIN Ling

Acta Agronomica Sinica. 2020, 46(9):  1368-1379.  doi:10.3724/SP.J.1006.2020.94188

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PIF4, which belongs to the phytochrome interacting factor family, is a key transcription factor in response to temperature changes, and is widely involved in plant heat signaling transduction and hormonal signaling pathways. In this study, the GhPIF4 gene was cloned from ‘YZ1’ (Gossypium hirsutum). Subcellular localization results indicated that GhPIF4 is a nuclear located protein. qRT-PCR analysis and GUS staining of proGhPIF4:GUS transgenic cotton plants showed that the GhPIF4 gene was highly expressed in the anther, and its expression was significantly induced by high temperature (HT) in the ‘H05’ (HT sensitive line). With the overexpression of GhPIF4, different cotton transgenic lines showed different male fertility performances. Three transgenic lines with high GhPIF4 expression, OE5, OE7, and OE19, showed indehiscent anthers in the flower on the day of flowering and lower pollen activity than wild type ‘YZ1’. However, the transgenic line OE10 with slighter overexpression showed normal anther dehiscence and pollen activity. These results indicated that GhPIF4 causes anther abortion in an expression level-dependent manner. Furthermore, the IAA content was measured in OE7 and OE19 anthers at the tapetum degradation stage (9-14 mm buds) and mitotic stage (14-19 mm buds). As a result, the IAA content in OE7 and OE19 decreased compared to that in ‘YZ1’. Then, we analyzed the expression of auxin biosynthesis genes, including GhTAA1, GhYUC2, and GhCYP71A13, showing that the expression of these genes was down-regulated in OE7 and OE19, which was consistent with the decrease in IAA content. We hypothesize that overexpression of GhPIF4 might partially simulate the response of late stage anthers to HT, while constitutive overexpression of GhPIF4 may alter the auxin content in vegetative organs or early stage anthers, or the decline of IAA may lead to the anther abortion. These results provide a reference for further analysis of the function of GhPIF4 gene and understanding the mechanism of cotton anther abortion under HT.

Association analysis of dormancy QTL in tetraploid potato via candidate gene markers

LI Jing-Cai, WANG Qiang-Lin, SONG Wei-Wu, HUANG Wei, XIAO Gui-Lin, WU Cheng-Jin, GU Qin, SONG Bo-Tao

Acta Agronomica Sinica. 2020, 46(9):  1380-1387.  doi:10.3724/SP.J.1006.2020.94200

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Dormancy is one of the prominent and important potato (Solanum tuberosum L.) tuber traits. Identifying the key genes regulated potato tuber dormancy and revealing its molecular mechanism to select potato varieties with desirable dormancy length are crucial to solve the economic losses and food safety issues due to the unsuitable dormancy length in potato industry. Previously, six additive dormancy QTLs were mapped in a linkage population of diploid potato. This study aimed to verify these QTLs in tetraploid potato breeding germplasm. Based on the candidate gene markers linked to the dormancy QTLs, we used a mixed linear model (MLM), taking the population structure and genetic relationship (Q+K) into account to conduct the association analysis of potato tuber dormancy in a natural tetraploid potato population St-hzau. The candidate gene markers S199_300 and GWD (derived from α-glucan water dikinase gene) linked to QTL DorB5.3 on chromosome 5 showed significant association with potato tuber dormancy (P < 0.05), which explained 7.8% and 3.2% of the phenotypic variation, respectively. The two markers could increase the dormancy length by 7.1 d and 4.5 d, respectively, revealing that the main effect of dormancy QTL DorB5.3 in the linkage population of diploid potato was also significant in the natural tetraploid potato population St-hzau. So the stability of DorB5.3 was validated in the association analysis, showing that the candidate gene marker strategy is an effective strategy in QTL association analysis of potato tuber dormancy. The major dormancy QTL DorB5.3 and corresponding linkage markers verified in this study could be directly used in potato dormancy breeding. According to the results, it could be proposed that GWD might play a role in controlling reducing-sugar content and dormancy of potato tuber, indicating a mechanism crosstalk between potato tuber dormancy and reducing-sugar content.

TILLAGE & CULTIVATION·PHYSIOLOGY & BIOCHEMISTRY

A method of defoliant application based on fiber damage and boll growth period of machine-harvested cotton

TIAN Jing-Shan, ZHANG Xu-Yi, WANG Wen-Min, YANG Yan-Long, SUI Long-Long, ZHANG Peng-Peng, ZHANG Ya-Li, ZHANG Wang-Feng, GOU Ling

Acta Agronomica Sinica. 2020, 46(9):  1388-1397.  doi:10.3724/SP.J.1006.2020.94196

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Defoliation technology is an essential prerequisite for machine-harvested cotton, and to apply defoliant to achieve better defoliation and improve fiber quality is an important method. The objective of this study was to analyze the quantitative relationship between fiber damage amount and boll growth period by defoliant. The results showed that defoliant had not significantly an effect on fiber length, which showed that all reduced by from 0.2% to 1.2% compared with the control, 46%-69% cotton varieties decreased or equal, whereas 31%-54% cotton varieties increased in fiber length compared with control. Fiber strength was affected significantly by defoliation, and the amplitude of fiber damage was concentrated between -4 cN tex^-1 and 0 cN tex^-1. The amount of fiber damage by defoliant was correlated to the spraying time in cotton boll growth, and the high damage at 30 days, whereas the lowest damage at 37 days. More than 61% cotton varieties showed an increased by average 1.1 cN tex^-1 on fiber strength compared with the control. Fiber strength damage because of defoliant increased with the increasing boll growth period. It was an indicator for determining the time of spraying defoliation based on the boll growth period and fiber damage (R_d/b) on fiber strength. Furthermore, cotton boll growth period and boll volume. Fiber strength and boll volume, boll volume and boll growth period, both showed significant positive correlation. If fiber strength of more than 31 cN tex^-1was produced in field, a cotton cultivar should be selected with boll volume of more than 31.8 cm³, boll growth period of more than 60.0 d and R_d/b more than 0.68. Defoliant used after 40.9 post-anthesis days could ensure fiber strength of less than 0.5 cN tex^-1.

TILLAGE & CULTIVATION·PHYSIOLOGY & BIOCHEMISTRY

Effects of micro ridge-furrow with plastic mulching on soil hydrothermal environment and photosynthesis at seedling stage of spring wheat on cold rain-fed area

HOU Hui-Zhi, ZHANG Xu-Cheng, FANG Yan-Jie, YU Xian-Feng, WANG Hong-Li, MA Yi-Fan, ZHANG Guo-Ping, LEI Kang-Ning

Acta Agronomica Sinica. 2020, 46(9):  1398-1407.  doi:10.3724/SP.J.1006.2020.01012

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The solution against drought and cold in spring was one of the most important factors which increased the yield of spring wheat in northwest of Loess Plateau (104°36′E, 35°35′N). The objective of the study was to evaluate the effects of micro ridge-furrow with plastic mulching (PRF) on soil temperature and moisture at the seedlings stage and the regulative mechanism of PRF on soil thermal-moisture and photosynthesis of spring wheat. The field experiments had been conducted using Longchun 35 from 2016 to 2018 in cold rain-fed area of northwest Loess Plateau. The three treatments were: 1) micro ridge-furrow with whole field plastic mulching (PRF), 2) whole field soil-plastic mulching (PMS), and 3) without mulching (CK). The parameters including soil temperature, soil water content, above-ground biomass, leaf SPAD, photosynthetic and transpiration rate, the soil water storage (SWS), periodical evaportranspiration (ET), growth rate, and water use efficiency (WUE) were measured at 18, 25, and 32 days after sowing (DAS), respectively. The results were as follows: the mean soil temperature within 0-25 cm profile treated with PRF and PMS compared with CK, was increased by 3.6°C, 3.0°C, 2.0°C and 2.9°C, 2.5°C, 1.7°C respectively, while those treated PRF compared to PMS increased by 1.3°C, 0.9°C, 0.9°C and 0.8°C, 0.7°C, 0.7°C within 0, 5, and 10 cm profile at 18, 25, and 32 days. The SWS treated with PRF and PMS compared to CK was on the rise by 7.3, 9.7, 12.6 mm and 3.9, 7.6, and 11.0 mm within 0-40 cm profile at 18, 25, and 32 days, respectively. While those treated PRF within 0-40 cm profile with 10 cm intervals compared to PMS risen by 1.1, 0.9, 0.8, 0.6 mm. The parameters treated with PRF and PMS at seeding stage including plant biomass, growth rate, leaf SPAD value, net photosynthetic rate and transpiration rate were significantly higher than those of CK, while those of PRF higher than PMS. Moreover, the yield and WUE of PRF were increased by 9.1%, 36.5%, and 5.9%, 30.8% than those of PMS and CK, respectively. Therefore, the treatment of PRF and PMS could effectively improve the ability of photosynthesis and plant growth by overcoming the cold and drought situation at the seedling stage, and PRF treatment was more effective than PMS.

TILLAGE & CULTIVATION·PHYSIOLOGY & BIOCHEMISTRY

Effect of mixed-sowing of near-isogenic lines on the clubroot disease controlling efficiency in rapeseed

GUO Qing-Yun, KUAI Jie, WANG Bo, LIU Fang, ZHANG Chun-Yu, LI Gen-Ze, ZHANG Yun-Yun, FU Ting-Dong, ZHOU Guang-Sheng

Acta Agronomica Sinica. 2020, 46(9):  1408-1415.  doi:10.3724/SP.J.1006.2020.04074

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The clubroot disease caused by Plasmodiophora brassicae has become a serious threat to rapeseed production in these recent years. In the previous multi-plot and multi-season field experiments, we found that planting of susceptible and resistant cultivars (near-isogenic lines) at different proportions could significantly suppress the incidence of the clubroot disease. In order to explore the preventive and control effect of mix-sowing of susceptible and resistant cultivars on clubroot disease, and identify the factors affecting mixed sowing. Pot experiments with different distance (0, 2, 4, and 6 cm) between the seeds of the resistant and susceptible cultivars were set by artificial inoculation at the 7 days after germination in this study. The disease incidence, disease index and the root biochemical components of rapeseed were measured after forty-two days. The results were as below: (1) the incidence of the resistant cultivar showed no significant change, while the disease incidence and disease index of the susceptible rapeseed cultivars decreased in the mixed-sowing treatment. Further, the disease incidence was significantly influenced by sowing distance of the two cultivars, which was significantly (P < 0.05) lower than those of the other treatments when mixed-sowed at 0 cm. (2) compared to the single planting, the content of soluble sugar and soluble protein in roots of the mixed-sowing treatment were significantly (P < 0.05) decreased for the two cultivars, and the content of acid-insoluble lignin was significantly increased in susceptible cultivar whereas decreased after increasing in resistant cultivar. (3) the results of correlation analysis showed that the content of soluble sugar and soluble protein were positively correlated with the disease incidence and disease index. The correlation coefficients between disease incidence and soluble sugar and soluble protein content were 0.797 and 0.403, respectively, meanwhile, the correlation coefficients between disease index and soluble sugar and soluble protein content were 0.822 and 0.509, respectively. In conclusion, the findings provided a new idea for prevention of clubroot disease in the field production in rapeseed.

Effects of chemical topping with fortified mepiquat chloride on photosynthetic characteristics of cotton leaves under different nitrogen rates

SHI Xiao-Juan, HAN Huan-Yong, WANG Fang-Yong, HAO Xian-Zhe, GAO Hong-Yun, LUO Hong-Hai

Acta Agronomica Sinica. 2020, 46(9):  1416-1429.  doi:10.3724/SP.J.1006.2020.94174

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This study aims to explore the effects of fortified mepiquat chloride (25% DPC, 1,1-dimethyl piperidinium chloride) on cotton leaf photosynthetic regulation under different nitrogen fertilizations. Field experiments were used Xinluzao 53 and conducted split plot arrangement with three nitrogen (N) fertilizer levels [150 (N₁), 300 (N₂), 450 (N₃) kg hm^-2] and three DPC⁺ doses [450 (P₁), 750 (P₂), 1050 (P₃) mL hm^-2]. Chlorophyll content, leaf area, gas exchange, chlorophyll fluorescence parameters and dry matter accumulation were investigated. With the increasing nitrogen application level, the chlorophyll content, leaf area, gas exchange parameters, chlorophyll fluorescence parameters and reproductive organs dry matter accumulation were increased first and then decreased. P₁N₁, P₂N₂, and P₃N₃ treatments had greater reproductive organ dry matter accumulation, chlorophyll content, net photosynthetic rate (P_n), actual photochemical efficiency (Ф_PSII), electron transfer rate (ETR), and lower non-photochemical quenching (NPQ). N₂P₂ treatment increased chlorophyll content, P_n, T_r, G_s, Ф_PSII, ETR, reproductive organs dry matter accumulation by 15.52%, 29.39%, 27.97%, 36.77%, 23.28%, 23.55%, 8.41%-22.24% respectively, while reduced NPQ by 34.54%, compared with other counterparts. The correlation analysis showed that the dry matter accumulation was significantly positively correlated with chlorophyll content, leaf area, P_n, G_s, Ф_PSII, and significantly negatively correlated with NPQ. In conclusion, the application of nitrogen fertilizer at 300 kg hm^-2 in combination with DPC⁺(750 mL hm^-2) improved leaf photosynthetic characteristics and promoted the distribution of photosynthates to reproductive organs due to increased dry matter accumulation.

Regulations of controlled irrigations and increased densities on yield formation of hybrid indica rice under nitrogen-reduction conditions

LI Min, LUO De-Qiang, JIANG Xue-Hai, JIANG Ming-Jin, JI Guang-Mei, LI Li-Jiang, ZHOU Wei-Jia

Acta Agronomica Sinica. 2020, 46(9):  1430-1447.  doi:10.3724/SP.J.1006.2020.02017

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Rice is one of the most important staple food crops of the world, both water management and plant density are crucial factors for the growth and development of rice. However, little information has been known about the combined effects of water management and plant density on grain yield under nitrogen-reduction conditions in rice. Field experiments were conducted in the farm of Rice Research Institute of Guizhou Agricultural Sciences Academy in 2017 and 2018. The hybrid indica rice cultivar Chengyou 981 was selected as the material, and the conventional high-yielding cultivation model as the control (CK), of which the nitrogen application rate (N₀) was 187.5 kg hm ^-2, the water management (W₀) was wet irrigation, and the plant density (D₀) was 20.0×10⁴hm^-2. Three models with increased density (W₀D₁: a density increased by 20%, W₀D₂: a density increased by 40%, and W₀D₃: a density increased by 60%) and nine combined models of controlled irrigation and increased density (W₁D₁, W₁D₂, W₁D₃, W₂D₁, W₂D₂, W₂D₃, W₃D₁, W₃D₂, and W₃D₃) were set to study the yield and its formation of rice under two nitrogen-reduction conditions. W₁, alternate wetting and light drying irrigation with -10 kPa of the minimum soil water potential; W₂, alternate wetting and moderate drying irrigation with -20 kPa of the minimum soil water potential; and W₃, alternate wetting and heavy drying irrigation with -30 kPa of the minimum soil water potential. The results were as follows: (1) When the nitrogen application was reduced by 10%, compared with CK, the grain yields of three increased density treatments were significantly decreased except W₀D₁, which had a slightly increased dry matter accumulation at maturity. Among the nine combined models of controlled water and increased density, the grain yields of W₁D₁ and W₂D₁ were 3.70% and 1.19% higher than that of CK, respectively. The effective panicle numbers of W₁D₁ and W₂D₁ were equivalent to that of CK, while the spikelet numbers per panicle decreased by 3.50% and 2.79%, seed-setting rates increased by 3.04% and 2.37%, and 1000-grain weights increased by 0.71% and 0.35%, respectively. Compared with CK, the higher grain yields of W₁D₁ and W₂D₁ were attributed to 3.88% and 5.54% higher percentage of productive tillers, 2.77% and 0.59% higher highly effective leaf area index at heading, 3.87% and 1.78% higher dry matter accumulation in panicles, 5.50% and 6.24% higher percentage of dry matter accumulation in panicles, 5.53% and 5.93% higher harvest index, and the equivalent total dry matter accumulation at maturity, respectively. (2) When the nitrogen application was reduced by 30%, the grain yields of nine combined models of controlled water and increased density were significantly decreased by 15.44%-30.85% as compared with CK. W₂D₂ and W₁D₂ had the smallest yield reductions. Therefore, the reasonable combined model of controlled water and increased density under a small amount of nitrogen-reduction could improve the growth characteristics of rice plants and increase grain yield, while the regulatory effects of controlled water and increased density became weaker and resulted in significantly lower grain yield under the excessive nitrogen-reduction.

RESEARCH NOTES

Estimation of ramie yield based on UAV (Unmanned Aerial Vehicle) remote sensing images

FU Hong-Yu, CUI Guo-Xian, LI Xu-Meng, SHE Wei, CUI Dan-Dan, ZHAO Liang, SU Xiao-Hui, WANG Ji-Long, CAO Xiao-Lan, LIU Jie-Yi, LIU Wan-Hui, WANG Xin-Hui

Acta Agronomica Sinica. 2020, 46(9):  1448-1455.  doi:10.3724/SP.J.1006.2020.04020

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This paper provides a new method to estimate ramie yield by integrating plant height and germplasm characteristics obtained by UAV-RGB system. The experiment was carried out in the ramie experimental area of Yunyuan base of Hunan Agricultural University in 2019, and the images of ramie in the seedling and mature stages were obtained by using a high-definition digital camera mounted on a drone. Firstly, Pix4D mapper was used to generate the digital surface model and ortho-image of ramie canopy in two growth periods. Based on the DSM, we used “difference method” to calculate the average plant height of the experimental plot. RGB channel mean value of experimental plot was extracted based on orthography, and then digital image variables and vegetation index were calculated. Then, the difference and diversity of spectral phenotypic characters and yield/plant height ratio characters among the germplasm of ramie were analyzed. Finally, stepwise regression method was used to establish the ramie yield prediction model, and correlation analysis was carried out for each yield interpretation factor. There was a significant correlation between DSM-based H and the measured plant height (r = 0.90), with RMSE of 0.04 for the linear model established based on the corrected plant height and the measured plant height. Plant height information was significantly correlated with yield (r = 0.91), while spectral phenotype information was not significantly correlated with yield. The ramie yield prediction model established by the fusion of plant height and germplasm characteristics was highly accurate, with R² of 0.85 and RMSE of 0.71. Therefore, this study has important practical significance for resource management and yield estimation of ramie germplasm.

Control effects of different potato varieties (lines) and rice-potato rotation system on root-knot nematode

WU Chao, LIU Xian-Wen, ZHANG Wei, WANG Qiong, GUO Hua-Chun

Acta Agronomica Sinica. 2020, 46(9):  1456-1463.  doi:10.3724/SP.J.1006.2020.94191

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Root-knot nematode disease, induced by Meloidogyne incognita and Meloidogyne javanica, is one of the main reasons of crop failure in potato continuous cropping in Yunnan province. Variety resistance evaluation, rice-potato rotation model and dynamic changes were studied in order to assess the protect-and-control treatment of potato root-knot nematode disease. Variety resistance evaluation, rice-potato rotation model and dynamic changes were all studied in order to evaluate the protect-and-control treatment of potato root-knot nematode disease. The results from the variety resistance evaluation indicated that among the 18 potato cultivars (lines) no resistant materials were screened resistant to both Meloidogyne incognita and Meloidogyne javanica, whereas the 1002-1 line and Lishu 6 displayed better disease resistance, Qingshu 9 and Cooperation 88 were more sensitive to potato root-knot nematode disease. All kinds of the egg, larva and imago of root-knot nematodes were simultaneously detected in soil with the root-knot nematodes disease. However, after rice-potato rotation, the egg, larva and imago of root-knot nematodes were to disappear entirely in soil, and the root knot nematode disease was no longer occurred in the following potato planting process. Furthermore, the tuber yield per plant of Qingshu 9, Cooperation 88 and Lishu 6 compared with control were significantly different increased by 50.5%, 43.7%, and 26.0%, respectively. These results suggested rice-potato rotation could be an effective way to control potato root knot nematode disease. In addition, to further analyzed the mechanism of rice-potato rotation inhibiting root-knot nematode survival, we observed the dynamic changes of the amount on root knot nematodes in the case of soil flooding. The results showed that no different states of the insect state were detected until submerged more than 60 days. Therefore, we speculated prolonged soil flooding may be the main reason for inhibiting the growth of root-knot nematodes. It is a sustainable and effective method to control potato root-knot nematode by selecting rice-potato rotation with disease-resistant varieties.