Table of Content

01 August 2021, Volume 54 Issue 15

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CROP GENETICS & BREEDING·GERMPLASM RESOURCES·MOLECULAR GENETICS

Identification and Gene Functional Analysis of Yellow Green Leaf Mutant ygl3 in Rice

XU ZiYi,CHENG Xing,SHEN Qi,ZHAO YaNan,TANG JiaYu,LIU Xi

Scientia Agricultura Sinica. 2021, 54(15):  3149-3157.  doi:10.3864/j.issn.0578-1752.2021.15.001

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【Objective】 To enrich and deepen people’s understanding of the molecular mechanism of plant leaf color, the phenotype identification and gene cloning of the yellow green leaf mutant ygl3 (yellow green leaf 3) were carried out to clarify the molecular function of YGL3 and lay the foundation for elucidating the molecular mechanism of YGL3 regulating rice leaf color.【Method】 Two stable genetic allelic yellow green leaf mutants, ygl3-1 and ygl3-2, were isolated from the CRISPR-Cas9 knockout mutant library of Zhonghua 11. The phenotype of the mutant was identified, and the chlorophyll contents of the wild-type and ygl3 were determined. The chloroplast structure of the wild-type and ygl3 was observed by transmission electron microscope. qRT-PCR was used to analyze the tissue expression of YGL3, and BioXM2.6 software was used for sequence alignment of YGL3 and its homologs. Yeast two hybrid was used to screen the interacting proteins of YGL3.【Result】 Compared with the wild type, the leaves of ygl3 were yellowing, and the contents of chlorophyll, carotenoid and total photosynthetic pigment at seedling stage in ygl3 were significantly decreased. Transmission electron microscopy showed that the chloroplast morphology of ygl3 was abnormal, and the thylakoid lamellar structure was less, whereas the chloroplast morphology of the wild type was normal and the thylakoid lamellar structure was orderly arranged. CRISPR-Cas9 knock-out site identification showed that the LOC_Os01g73450 gene had a single base insertion, which resulted in the early termination of protein translation. The gene encoding 351 amino acids was mutated into a truncated protein with 55 amino acids. Compared with the wild type, the expression level of LOC_Os01g73450 was significantly down-regulated in the mutants. qRT-PCR showed that YGL3 was expressed in roots, panicles, seeds, leaf sheaths and leaves. YGL3 was highly expressed in leaves. YGL3 encodes a plastid localized UMP kinase. The YGL3 protein was conserved in Zea mays, Sorghum bicolor and Arabidopsis thaliana. YGL3 shared the high sequence homology (59.4% amino acid identity) to Arabidopsis. qRT-PCR showed that chlorophyll synthesis genes, including HEMC, HEMC and URO-D, were significantly down-regulated in ygl3, whereas the expression levels of HEMB, HEMF and HEML were no significant difference between the wild type and ygl3. Yeast two hybrid screen showed that YGL3 interacted with RNA editing factor MORF8.【Conclusion】 The phenotype of the yellow leaf mutant ygl3 resulted from the LOC_Os01g73450 mutation. YGL3 was an allele of the yellow green leave gene YL2/YGL8. YGL3 was highly expressed in leaves, and YGL3 interacted with MORF8 in yeasts.

Characterization of Wheat Cultivar Zhongmai 895 with High Yield Potential, Broad Adaptability, and Good Quality

ZHANG Yong,YAN Jun,XIAO YongGui,HAO YuanFeng,ZHANG Yan,XU KaiJie,CAO ShuangHe,TIAN YuBing,LI SiMin,YAN JunLiang,ZHANG ZhaoXing,CHEN XinMin,WANG DeSen,XIA XianChun,HE ZhongHu

Scientia Agricultura Sinica. 2021, 54(15):  3158-3167.  doi:10.3864/j.issn.0578-1752.2021.15.002

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Characterization of leading cultivars will provide crucially important information for cultivar development. The objective of this research is to characterize high yield potential, broad adaptation, good disease resistance and stress tolerance, as well as good quality in wheat cultivar Zhongmai 895. The dataset of two populations of Zhongmai 871/Zhongmai 895 recombinant inbred lines and Yangmai 16/Zhongmai 895 doubled haploids, as well as regional yield and pilot trial related with Zhongmai 895 were used in this research. The high yield potential of Zhongmai 895 was largely due to the increased spike number which could easily reach 640/m², guaranteed by erect plant type with small leaves, and short plant height around 75 cm related to the outstanding lodging resistance, on the basis of two QTL for tiller angle, five QTL for leaf angle, and combination of semi dwarfing genes Rht2 and Rht24. It was characterized with high and stable thousand grain weight (48 g) related to the fast grain filling rate which provided excellent tolerance to high temperature during grain filling period, contributing to the perfect performance in late sowing environment, together with the contribution from high water and fertilizer use efficiency, high activity of root system, and slow leaf senescence, on the basis of four QTL for high thousand grain weight and grain filling rate, five genes for drought tolerance with vernalization gene combination of vrn-A1x, Vrn-B1a, and vrn-D1w. The performance of the broad adaptability was further contributed by the good resistance to stripe rust, powdery mildew and Fusarium head blight in the production, due to the presence of one major QTL for stripe rust resistance, two QTL for slow powdery mildew, and one new QTL for Fusarium head blight resistance. Zhongmai 895 was one of the few cultivars performing good dual qualities for Chinese dry white noodles and steamed bread with stable medium gluten strength, bright and yellow flour colour across environments in the Yellow-Huai River Valleys Winter Wheat Region, with Glu-A3d, and performed high nutrition quality with stable and high phenolic acid concentration of 748 μg·g^-1. This research provides very important information and experience for developing new cultivars with high yield potential and broad adaptability.

Mapping QTL for Soybean Fatty Acid Composition Based on RIL and CSSL Population

QU KeXin,HAN Lu,XIE JianGuo,PAN WenJing,ZHANG ZeXin,XIN DaWei,LIU ChunYan,CHEN QingShan,QI ZhaoMing

Scientia Agricultura Sinica. 2021, 54(15):  3168-3182.  doi:10.3864/j.issn.0578-1752.2021.15.003

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【Objective】 Soybeans (Glycine max) originated from China. High-quality soybeans are widely used in various processing industries such as food, feeding, textiles, etc. Therefore, high-quality soybean breeding is a key point for soybean breeders and producers. This study conducted QTL mapping of each component of soybean fatty acid and screening of candidate genes, which would lay the molecular foundation for soybean quality improvement. 【Method】 A recombinant inbred lines (RILs) population crossed by Charleston (American soybean varieties ) and Dongnong 594, and a chromosome segment substitution lines (CSSLs) population crossed by Suinong 14 (cultivated soybean) and ZYD00006 (wild soybean) were used for QTL mapping. We used gas chromatography to determine the fatty acid content of these two populations. As the genetic maps have been published by the soybean genetic improvement laboratory of the Agricultural College of Northeast Agricultural University before, QTL mapping of soybean fatty acid components in RIL and CSL populations were performed by the Windows QTL Cartographer 2.5 and ICIMapping software. And the candidate genes were screened from the QTL interval. 【Result】 Based on 2017 to 2018 years data, 34 and 20 QTLs related to fatty acid components were mapped in the RIL population and the CSSL population, respectively. These QTLs distribute in 13 linkage groups except B2, C1, G, H, J, M, and O. QTL mapping of the two populations was compared that ten pairs of QTLs were detected in the two populations. We found that QTLs distributed in the A1, C2, D1a, F, K, and N linkage groups were related to the content of multiple fatty acids components. An overlapping QTL related to linoleic acid and oil content was detected on the A1 linkage group, QTL related to stearic acid and oil content on the C2, QTL related to stearic acid and oil content on the D1a, QTLs related to palmitic acid, stearic acid and oil content on the F, QTLs related to linoleic acid and linolenic acid content on the K, QTLs related to palmitic acid and oil content, and QTL related to oleic acid and linoleic acid content on the N. Candidate genes were screened out from QTL intervals. In total, 485 candidate genes were screened from the gene annotation data set and 271 of them annotated within GO annotations. GO enrichment analysis showed that 15 candidate genes involved in fatty acids pathway. These genes affect synthesis of fatty acids mainly through encoding plant acyl carrier protein (ACP) thioesterase, fatty acid desaturase, phospholipase D1, fatty acid-hydroxylase and pyruvate kinase, participating in the biosynthesis of acyl-CoA, and regulating the extension of fatty acid chain. 【Conclusion】 54 QTLs related to soybean fatty acid were detected, and 10 pairs QTLs were stable detected from the two mapping populations. We used the confidence intervals from QTL mapping to screen candidate genes, and 15 candidate genes related to fatty acids pathway were screened out. These stable QTLs and candidate genes can be used for molecular marker-assisted selection of soybean fatty acid improvement.

TILLAGE & CULTIVATION·PHYSIOLOGY & BIOCHEMISTRY·AGRICULTURE INFORMATION TECHNOLOGY

Regulation Effects of Water Saving and Nitrogen Reduction on Dry Matter and Nitrogen Accumulation, Transportation and Yield of Summer Maize

WANG XuMin,LUO WenHe,LIU PengZhao,ZHANG Qi,WANG Rui,LI Jun

Scientia Agricultura Sinica. 2021, 54(15):  3183-3197.  doi:10.3864/j.issn.0578-1752.2021.15.004

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【Objective】 In order to solve the problems of irrigation water resources scarcity and excessive nitrogen input in current summer maize cropping system, this study analyzed the regulating effects of maize growth and yield response between water-saving, nitrogen reduction mode and conventional water-nitrogen mode, so as to provide a theoretical basis for determining water-saving and nitrogen-reduction cultivation measures of summer maize. 【Method】 A different irrigation and nitrogen application field trial of summer maize was conducted in Yangling, Shaanxi province in 2018-2019. Three irrigation treatments were conventional irrigation (800 m³·hm^-2), reduced irrigation (400 m³·hm^-2) and no irrigation (0); and five nitrogen treatments were as follows: conventional nitrogen application (300 kg N·hm^-2), reduced 25% (225 kg N·hm^-2), reduced 50% (150 kg N·hm^-2), reduced 75% (75 kg N·hm^-2) and no N fertilizer(0), respectively. The study investigated the effects of water saving and nitrogen reduction on maize yield, photosynthetic characteristics, dry matter (nitrogen) accumulation and its transport characteristics.【Result】 (1) Compared with conventional water-nitrogen mode (conventional irrigation and 300 kg N·hm^-2), the water-saving and nitrogen reduction mode (reduced irrigation and 225 kg N·hm^-2) had no significant effect on maize yield and its components. (2) Compared with conventional water-nitrogen mode, the reduced irrigation and 225 kg N·hm^-2 treatment had no impact on maize leaf area index (LAI), its LAI increased obviously before anthesis and decreased slowly after anthesis than that under other treatments. The net photosynthetic rate of ear leaf significantly increased by 10.0% at tasseling stage, and kept a higher net photosynthetic rate till the post anthesis period, this promoted the dry matter accumulation. (3) Reduced irrigation and 225 kg N·hm^-2 had no remarkable influence on dry matter accumulation, but the maximum growth rate of dry matter accumulation was significantly increased by 6.3%, and occurred 0.8 days earlier. (4) The dry matter remobilization, remobilization efficiency and contribution of remobilization to grain efficiency in pre-anthesis of reduced irrigation and 225 kg N·hm^-2 treatment increased significantly by 36.4%, 40.1% and 28.6%, respectively. The nitrogen remobilization, remobilization efficiency and contribution of nitrogen remobilization to grain efficiency pre-anthesis increased significantly by 30.3%, 22.0% and 42.1%, respectively. However, there was no difference in dry matter (nitrogen) accumulation and contribution efficiency to grain under the two type water and nitrogen modes. 【Conclusion】 Comprehensively, the water-saving and nitrogen reduction mode (400 m³·hm^-2 irrigation amount and 225 kg N·hm^-2) could effectively coordinate dry matter (nitrogen) accumulation and its transportation, and increased the distribution ratio of dry matter and nitrogen in maize grain, which could achieve the production goal of water saving and nitrogen reduction of summer maize in Guanzhong plain.

Effects of Different Magnesium Supplies on the Growth and Physiological Characteristics of Oilseed Rape in Seeding Stage

WANG KunJiao,REN Tao,LU ZhiFeng,LU JianWei

Scientia Agricultura Sinica. 2021, 54(15):  3198-3206.  doi:10.3864/j.issn.0578-1752.2021.15.005

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【Objective】 Revealing the effects of different magnesium (Mg) supplies on the growth of oilseed rape, and providing a theoretical basis for the scientific application of magnesium fertilizer. 【Method】 Hydroponic experiments with 12 contrasting Mg supplies were conducted to evaluate the effects of different Mg supplies on growth, nutrient accumulation, photosynthetic characteristics, assimilate transport, and ion homeostasis of oilseed rape seedlings, and the critical Mg concentration was established, which was suitable for rapeseed growth. 【Result】 With the increasing Mg supplies, the rapeseed shoot biomass initially increased and then peaked at a concentration of 1.0 mmol·L^-1, and finally decreased when solution Mg continuous to increase. Here a biomass-based Mg concentration threshold where the relative biomass researched 95% of the maximum biomass was defined. It was indicated that the shoot Mg concentration of 0.4%-0.7% was suitable for rapeseed growth under hydroponic condition. Appropriate Mg nutrient supply promoted the growth of shoot and root of oilseed rape. Mg deficiency significantly decreased the leaf net photosynthesis rate, Rubisco enzyme activity, apparent electron transfer rate and maximum carboxylation rate, etc., and inhibited leaf carbohydrate transport and plant growth. Excessive Mg supply disturbed the potassium (K), calcium (Ca), and Mg balance, which ultimately reduced the leaf K and Ca uptake and limited the growth of oilseed rape. 【Conclusion】 Overall, the proper Mg nutrition increased the synthesis of photoassimilates, promoted the transportation and distribution of carbohydrates, ensured ion homeostasis, and in turn, promoted the growth of oilseed rape and seed yield.

Design and Implementation of Agricultural Transfer Payment Project Management System Based on Micro-Service Architecture

YAO Yan,NIU MingLei,SUN FaJun,YAO JingChan,CHANG XiaoYan

Scientia Agricultura Sinica. 2021, 54(15):  3207-3218.  doi:10.3864/j.issn.0578-1752.2021.15.006

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【Objective】 The central agricultural transfer payment has a large amount of funds and many types of projects. In order to improve the monitoring and supervision level of agricultural transfer payment projects and the management level of agricultural transfer payment projects, based on the in-depth study and analysis of the project management business of agricultural transfer payment, this paper developed and established the project management system of national agricultural transfer payment, so as to provide a convenient and efficient project management tool for the project management personnel of the central, provincial, municipal and county-level agricultural administrative departments. 【Method】 Agricultural transfer payment projects were characterized by diverse types and complex structure, and the system development adopts micro-service architecture to realize the technical construction of the system. The system was divided into nine function modules, which were independent and interrelated in business logic and could work together. They were: (1) Project notification module. This module provided various notices of transfer payment issued by the ministry level to each provincial level, and realized some functions, such as classified inquiry; (2) Project scheme module. This module provided the provincial level report of various project implementation plans for comments and key project plans to the ministry level; (3) Task list module. This module provided the task list of projects issued by the ministry to the provincial level; (4) Fund arrangement module (provincial filling in). This module provided the detailed data of the arrangement and use of special task funds reported from the provincial level to the ministry level; (5) Fund execution module (county-level filling in). This module provided county-municipal-provincial-ministry level reporting of project fund execution information level by level; (6) Performance objective module. This module provided the ministry level to decompose and issue performance objectives to the provincial level, and the provincial level to report the performance objectives to the ministry level; (7) Special dispatch module. This module provided the relevant data information of special dispatching task reported from the provincial level to the ministry level; (8) Statistical query analysis module. This module mainly carried out statistical analysis of project information reported by the county level of transfer payment, and presented relevant statistics and analysis results in the form of thematic charts; (9) System configuration module. This module mainly provided the dynamic adjustment and configuration of the name, expenditure direction and task of each special project. 【Result】 Through the in-depth analysis and design of system architecture, business process, functional modules and database design, the dynamic monitoring management system of “central-provincial-municipal-county (district) level” was constructed, which solved the problem that agricultural transfer payment project was difficult to fine management.【Conclusion】 The research results showed that the agricultural transfer payment project management system based on micro-service architecture realized the fine management of various special tasks of agricultural transfer payment by the central agricultural administrative department. The system could support 3 000 users all over the country to log in at the same time, and the response speed of system uploading and reporting was 2.29 s. The system provided the important technical support for the central agricultural authorities to strengthen supervision objectives, improve supervision efficiency, and organize on-site verification of performance evaluation of transfer payment projects. It had reference significance for agricultural authorities at all levels to improve the informatization construction of agricultural and rural investment project management.

PLANT PROTECTION

Identification of Xylosidase Genes from Verticillium dahliae and Functional Analysis Based on HIGS Technology

ZHANG XiaoXue,SUN TianGe,ZHANG YingChun,CHEN LiHua,ZHANG XinYu,LI YanJun,SUN Jie

Scientia Agricultura Sinica. 2021, 54(15):  3219-3231.  doi:10.3864/j.issn.0578-1752.2021.15.007

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【Objective】 The objective of this research is to identify xylosidase genes from Verticillium dahliae and study the relationship between xylosidase genes and pathogenicity of V. dahliae, which will provide a theoretical basis for exploring the molecular mechanism of pathogenicity of V. dahliae and a scientific basis for formulating better control strategies for verticillium wilt.【Method】 All xylosidase genes were identified from the genome database of V. dahliae by bioinformatics, and their protein domain, chromosomal location and phylogenetic relationship were analyzed. Quantitative real-time PCR (qRT-PCR) was used to detect the expression pattern of xylosidase genes in V. dahliae cultured with different root exudates from resistant and susceptible cotton varieties for 0, 6, 12, 24 and 48 h. The function of one of the xylosidase genes VdxyL3 in the infection of V. dahliae was analyzed by using host-induced gene silencing (HIGS) method. The target fragment of VdxyL3 was injected into cotton, and then V. dahliae Vd991 was inoculated to those plants injected with target fragment of VdxyL3 by using root-dip approach. The phenotype of transformed plants was observed and the disease index was counted, meanwhile, the biomass of fungi and the expression level of VdxyL3 in the plants were detected by qRT-PCR technique.【Result】 Bioinformatics analysis showed that there were 13 xylosidase genes (VdxyL1-VdxyL13) in V. dahliae, whose coding sequences ranged from 1 461 to 2 544 bp, molecular weight of the encoded proteins ranged from 38.78 to 90.97 kD, and theoretical isoelectric point ranged from 4.67 to 5.89. Protein domain phylogenetic relationship analysis showed that there were 9 glycoside hydrolase 43 family members, 1 glycoside hydrolase 3 family member and 3 glycoside hydrolase 31 family members included in xylosidase genes. The chromosomal location analysis showed that the 13 genes were distributed on 6 chromosomes and no gene clusters were formed. qRT-PCR analysis showed that the expression of 6 xylosidase genes was induced by cotton root exudates. After being cultured in one or more root exudates for 6 h or 12 h, expression levels of these genes were significantly increased and then decreased. Among 6 genes, the expression level of VdxyL3 increased significantly after sensing root exudates from sea island cotton. The results based on HIGS technology showed that after 14 and 21 days of inoculation, the disease symptom of cotton plants transformed with VdxyL3 interfering fragment was more serious, and the disease index (33.3 and 83.9) was significantly higher than that of empty vector control (21.7 and 66.1). qRT-PCR analysis showed that cotton plants transformed with VdxyL3 interfering fragment had higher fungal biomass but lower expression level of VdxyL3 compared to the empty vector control.【Conclusion】 The VdxyL3 gene silencing by using HIGS technology lead to a significant decrease of cotton resistance to V. dahliae, indicating that VdxyL3 may play a certain role in the pathogenesis of V. dahliae and host-pathogen interaction.

An Investigation into Key Factors Influencing the Occurrence of Virus Disease in Sweet Potato

ZHAO FuMei,WANG Shuang,TIAN YuTing,QIAO Qi,WANG YongJiang,ZHANG DeSheng,ZHANG ZhenChen

Scientia Agricultura Sinica. 2021, 54(15):  3232-3240.  doi:10.3864/j.issn.0578-1752.2021.15.008

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【Objective】 This study aimed to clarify the relationship between sweet potato virus types in storage roots and virus incidence and severity on root sprouts, and the relationship between numbers and SPCSV-carrying rate of Bemisia tabaci and SPCSV-carrying rate of storage roots, establish the prediction method and early warning technology for viral disease in sweet potato seedlings, so as to provide the theoretical basis for virus-free storage root production, and prevention and control of virus disease in sweet potato.【Method】 PCR and RT-PCR were performed to detect eight major sweet potato viruses including sweet potato feathery mottle virus (SPFMV), sweet potato virus C (SPVC), sweet potato virus G (SPVG), sweet potato latent virus (SPLV) and sweet potato virus 2 (SPV2) in the genus of Potyvirus, sweet potato chlorotic stunt virus (SPCSV) in the genus of Crinivirus, cucumber mosaic virus (CMV) in the genus of Cucumovirus, and sweepoviruses in the genus of Begomovirus in China in storage roots collected from different sources. The PCR-detected roots were planted in plastic pots and allowed to sprout under greenhouse conditions. The types and severity scores of viral symptoms on root sprouts were surveyed and recorded to analyze the relationship between virus species in roots and virus symptom severity on root sprouts. Virus-eliminated sweet potato cultivar Shangshu 19 (S19) plants with the same source were cultivated in the different locations in Henan, Ningxia and Shaanxi in 2018 and 2019. The number of B. tabaci in each test site was calculated by using yellow sticky traps, and was sampled for SPCSV detection during the growth period of sweet potato. The roots selected randomly from each test site were used for SPCSV detection after harvesting to analyze the relationship between numbers and SPCSV-carrying rate of B. tabaci and SPCSV-carrying rate of storage roots.【Result】 Of the 665 storage roots, 463 were infected with one or more of the eight viruses. After root sprouting, visual symptoms, such as leaf chlorosis, vein-clearing, rugosity and stunting were observed on the 333 root sprouts. Virus severity scores on root sprouts ranged from 0 to 1 (60.6% for score of 0 and 31.8% for score of 1) when roots were infected with potyvirus (es). Virus severity scores on root sprouts ranged from 0 to 1 (55.3% for score of 0 and 32.9% for score of 1) when roots were infected with sweepoviruses or co-infected with sweepoviruses and potyvirus (es). Root sprouts were observed with more severe symptoms when roots carried SPCSV, especially the combination of SPCSV and potyvirus (es), which caused visible symptoms on all sprouts with severity scores from 3 to 9 (49.0% for scores of 3 and 5, 51.0% for scores of 7 and 9). Results from two successive years field trial revealed that there was a positive correlation between SPCSV-carrying rate (X₁) and numbers (X₂) of B. tabaci and SPCSV-carrying rate (Y) of storage roots, and the equation of linear regression was Y=9.628X₁+0.008X₂+6.537, R²=0.914.【Conclusion】 Storage root carrying SPCSV is the key factor for serious occurrence of sweet potato viruses at seedling stage. Viral symptom appearance rate and severity scores increase significantly when roots are co-infected with SPCSV and potyvirus (es). There is a positive correlation between SPCSV-carrying rate and numbers of B. tabaci and SPCSV-carrying rate of storage roots, indicating that B. tabaci is the key factor influencing the SPCSV-carrying rate of storage root.

Establishment of RT-RPA for Citrus Yellow Vein Clearing Virus (CYVCV) Detection

MA ZhiMin,XU JianJian,DUAN Yu,WANG ChunQing,SU Yue,ZHANG Qi,BIN Yu,ZHOU ChangYong,SONG Zhen

Scientia Agricultura Sinica. 2021, 54(15):  3241-3249.  doi:10.3864/j.issn.0578-1752.2021.15.009

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【Objective】 The objective of this study is to establish a fast, simple, accurate and visualized with naked eyes new detection method for citrus yellow vein clearing virus (CYVCV) using reverse transcription-recombinase polymerase amplification (RT-RPA) combined with lateral flow dipstick (LFD).【Method】 Five pairs of primers were designed according to the conservative sequence of the coat protein gene of CYVCV. By detecting different samples, the pair of primers with the best amplification efficiency and specificity was selected. The selected primers were modified and its corresponding specific probe was designed. According setting 6 reaction gradient times (5, 10, 20, 30, 40 and 50 min) and 8 reaction gradient temperatures (37, 38, 39, 40, 41, 42, 43 and 44℃), the RT-RPA system for CYVCV detection was optimized. The specificity of the established RT-RPA was evaluated by detecting the samples infected with CYVCV, citrus leaf blotch virus (CLBV), citrus tristeza virus (CTV), citrus tatter leaf virus (CTLV), citrus exocortis viroid (CEVd), citrus psorosis virus (CPV), satsuma dwarf virus (SDV), Candidatus Liberibacter asiaticus (CLas) and Xanthomonas citri subsp. citri (Xcc), respectively. The citrus total RNA samples infected with CYVCV was diluted by 10 times. The original RNA solution and 10^-1, 10^-2, 10^-3, 10^-4, 10^-5, 10^-6, 10^-7 dilutions were used as templates for testing the sensitivity of RT-RPA, and the sensitivity was compared with RT-PCR. Leaves of different citrus varieties were randomly collected from the field. RT-RPA and RT-PCR were used at the same time to test the applicability of the established RT-RPA detection method.【Result】 A RT-RPA detection system for CYVCV was established, with primer pairs CY1-F/R and corresponding probe CY1 (47 bp). It could specifically amplify the target fragment of CYVCV with a size of 177 bp. The best reaction conditions were 39℃, 30 min. The result could be judged by the LFD test strip directly. In the specific test, only samples infected with CYVCV were positive, and the rest were negative. In the sensitivity detection, 10^-4 dilution was the lowest detection sensitivity of RT-RPA and RT-PCR. The sensitivity of the two methods was equivalent. Among the 45 field citrus samples taken randomly, 37 samples were positive by RT-PCR and RT-RPA, and the positive rate was both 82.2%, indicating that the RT-RPA method established in this study was stable and reliable.【Conclusion】 A RT-RPA detection method for CYVCV is established. The method is convenient, rapid, and visualized. It can be applied to on-site rapid detection for the labs with insufficient basic conditions or plant protection and quarantine station.

SOIL & FERTILIZER·WATER-SAVING IRRIGATION·AGROECOLOGY & ENVIRONMENT

Identification of Functional Substances from Rice Straw Obtained by Pyrolysis and Enzymolysis and Its Effect

TANG SiYu,LIU QiuMei,MENG XiaoHui,MA Lei,LIU DongYang,HUANG QiWei,SHEN QiRong

Scientia Agricultura Sinica. 2021, 54(15):  3250-3263.  doi:10.3864/j.issn.0578-1752.2021.15.010

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【Objective】 To explore the effect of agricultural wastes (rice straw) on plant growth, the identification and analyzation of the small molecules that may exist in the high-temperature extracts and enzymolysis solution of rice straw were performed, and the promoting effect of these substances on cucumber growth was also evaluated.【Method】 The high-temperature extract solution of rice straw was prepared by high temperature water extraction at 115℃ for 30 min. The condensation of the extracellular proteins from Trichoderma guizhouense NJAU 4742 under the induction of rice straw was obtained by ammonium sulfate precipitation method, which was used to hydrolyze the rice straw to prepare rice straw enzymatic hydrolysate. The high-temperature extract and enzymolysis solution of rice straw were diluted into different times, and the growth-promoting effects were verified by cucumber hydroponic experiment. The high-temperature extract and enzymatic hydrolysis of rice straw were identified and compared by UHPLC-QE-MS non-target metabolomics detection technology. Under the control of the acquisition software (Xcalibur 4.0.27, Thermo), the QE mass spectrometer collects primary and secondary mass spectrometry data in the information-related acquisition mode for the high-temperature extract and enzymatic hydrolysate of rice straw. Through the self-written R program package (the kernel was XCMS), the original data was processed for peak identification, peak extraction, peak alignment and integration, and then it was matched with the BiotreeDB (V2.1) self-built MS database for substance annotation. Finally, the growth-promoting effects of some identified substances were verified by the cucumber hydroponic experiment.【Result】 The results showed that both high-temperature extract and enzymatic hydrolysate liquid of rice straw could promote the growth of cucumber seedlings at appropriate concentrations, and the enzymatic hydrolysate of rice straw showed significant growth promoting effect on cucumber when diluted for 100 times. Compared with the CK, the dry weight of overground part, underground part and plant height of cucumber plants treated with 100 times dilution increased by 52.64%, 55.05% and 21.43%, respectively, and the number of plant root tips increased by 31.95%. The high-temperature extract of rice straw owned the best growth promotion effect when it was diluted 50 times, in which the dry weight of overground part, the underground part and the plant height of cucumber plants increased by 44.16%, 63.38% and 55.56%, respectively, and the number of plant root tips increased by 64.44%, compared with CK. The UHPLC-QE-MS non-target detection technology results showed that 714 different substances were identified in the high-temperature extract of rice straw and 638 different substances were identified in the enzymatic hydrolysis solution, among which acetylcholine, L-carnitine and myo-inositol were screened out. Meanwhile, the standard products of these three substances were added to the cucumber root system, and the results showed that they all had considerable promotion effect on cucumber growth. Acetylcholine at the concentration of 1 μmol·L^-1, 10 μmol·L^-1 and 100 μmol·L^-1 could all promote the growth of cucumber. Compared with CK, the exogenous acetylcholine at 1 μmol·L^-1 concentration increases the dry weight of cucumber shoots by 54.69% and the dry weight of roots by 73.67%, the number of root tips increased by 130.5%; Exogenous L-carnitine was beneficial to the growth of cucumber plants at the concentration of 0.1 mmol·L^-1 and 1 mmol·L^-1. Compared with CK, the dry weight of cucumber shoots increased by 33.79% and 30.19%, and the dry weight of roots increased by 44.97% and 48.82%, the number of cucumber root tips increased by 41.8% and 49.9%, respectively; Exogenous myo-inositol at the concentration of 0.05 mmol·L^-1 and 0.1 mmol·L^-1 could promote the growth of cucumber. Compared with CK, the dry weight of cucumber shoots increased by 36.66% and 30.15%, roots dry weight increased by 69.82% and 51.78%, and the number of cucumber root tips increased by 149.0% and 96.7%, respectively.【Conclusion】 In brief, both the high-temperature extract and the enzymatic hydrolysate of rice straw could significantly promote the growth of cucumber, and the acetylcholine, L-carnitine and myo-inositol were detected by LCMS in the pyrolysis and enzymatic hydrolysate of rice straw, which were considered as the functional substances in rice straw.

Effects of Drip Irrigation Methods on Photosynthetic Characteristics, Yield and Irrigation Water Use of Apple

LIU Xing,CAO HongXia,LIAO Yang,ZHOU ChenGuang,LI HuangTao

Scientia Agricultura Sinica. 2021, 54(15):  3264-3278.  doi:10.3864/j.issn.0578-1752.2021.15.011

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【Objective】 The aim of this study was to explore a high-efficient production drip irrigation model of apple tree in Loess Plateau.【Method】 In this study, 8-year-old Hanfu apple trees were took as the research object with different irrigation amount and pattern experiments. These experiments were divided into three treatment groups of root-divided alternative irrigation(ADI), single pipe drip irrigation(UDI) and double pipe drip irrigation(BDI). ADI, UDI and BDI were supplied with three different irrigation levels: high water (W1), middle water (W2) and low water (W3), respectively. Therefore, there were nine treatments based on orthogonal experiment design in number. Then, the responses of the important apple tree parameters, including canopy structure, photosynthetic characteristics, yield and irrigation efficiency, were studied.【Result】 The results showed that less irrigation amount (W2 and W3) significantly reduced leaf area index, leaf inclination angle and clumping index (P<0.05), and increase the irrigation water use efficiency. Compared with single pipe drip irrigation, the drip pattern of alternate root division significantly increased leaf area index (P<0.05), and significantly decreased leaf inclination angle and clumping index (P<0.05). The net photosynthetic rate, transpiration rate, stomatal conductance and carboxylation efficiency of apple leaves at 11:00 increased at first and then decreased with the increase of DAF. At the fruit expansion stage (DAF=80 d), the net photosynthetic rate, carboxylation efficiency and leaf instantaneous water use efficiency under ADI-W2 were higher than that under other patterns. The diurnal variation curve of net photosynthetic rate of apple leaves under different water treatments showed “M” pattern. The phenomenon of “midday depression” of net photosynthetic rate under ADI treatment was not obvious. The peak value of instantaneous water use efficiency of leaves of all treatments appeared at 10:00 a.m, besides the treatment of ADI-W2. ADI-W2 delayed the emergence of peak value, and exhibited a highest daily average instantaneous water use efficiency (3.22 μmol·mmol^-1). Furthermore, ADI-W2 had the best hardness (9.09 kg·cm^-2), fruit shape index (0.88), big fruit rate (63.46%), single fruit weight (224.12 g) and yield (33 010.15 kg·hm^-2). The combination with W3 could improve the irrigation water use efficiency, and the irrigation water use efficiency under ADI-W3 treatment (36.21 kg·m^-3) was the highest.【Conclusion】 Finally, ADI-W2 treatment could be defined to be the best drip irrigation mode of water-saving and yield increasing of apple comprehensive scoring method in Loess Plateau area in this study. The results provided a scientific theoretical support for apple drip irrigation management in Loess Plateau.

HORTICULTURE

The Carotenoid Cleavage Dioxygenases Gene AgCCD4 Regulates the Pigmentation of Celery Tissues with Different Colors

WANG Hao,YIN Lian,LIU JieXia,JIA LiLi,DING Xu,SHEN Di,FENG Kai,XU ZhiSheng,XIONG AiSheng

Scientia Agricultura Sinica. 2021, 54(15):  3279-3294.  doi:10.3864/j.issn.0578-1752.2021.15.012

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【Objective】 The genotype and relative expression level of carotenoid cleavage dioxygenases gene AgCCD4 in celery with different colors were revealed, and the roles of AgCCD4 gene on carotenoids accumulation in celery tissues were preliminarily analyzed combined with the corresponding carotenoids level, which laid a foundation for further study on the roles of CCD subfamily genes in the pigmentation of different colored celery tissues. 【Method】 The CCD family gene, AgCCD4, was obtained by homology search from genome of celery, and cloned from celery cvs. Jinnan Shiqin, Huangtaiji, Zigan NO.1, and Saixue, respectively. The composition of amino acids, physicochemical properties, genetic relationship, and spatial structure of proteins were analyzed by bioinformatics. The conservative domain and secondary structure were predicted and the tertiary structure model was established. Real-time quantitative PCR (RT-qPCR) was used to detect the expression levels of AgCCD4 in different tissues of celery with different colors. The contents of lutein and β-carotene of leaf blades, petioles, and roots of celery were determined by ultra-performance liquid chromatography (UPLC). The subcellular localization of AgCCD4 protein in tobacco epidermal cells was performed by using Agrobacterium-mediated transient expression system. 【Result】 Sequence analysis results showed that AgCCD4 contained an open reading frame (ORF) with the length of 1 779 bp, encoding 592 amino acids. A total of 18 nucleotides and 9 amino acids sites of AgCCD4s differed in the Saixue and other three celery varieties. The relative molecular weights of AgCCD4 from Saixue and other three celeries were 65.07 and 65.12 kD, and the theoretical pIs were 6.03 and 5.95, respectively. Phylogenetic analysis demonstrated that the CCD4 in celery had the closest genetic relationship with sunflower and lettuce from Compositae family. The secondary structure of AgCCD4 contained multiple α helices and random coils, and the tertiary structure was mainly composed of β strands. Lutein and β-carotene were not detected in celery roots. The contents of lutein and β-carotene in the leaf blades were the highest in Jinnan Shiqin (1 102.58 μg∙g^-1 DW and 241.92 μg∙g^-1 DW, resptectivey), whereas the lowest in Zigan NO.1 (57.12 μg∙g^-1 DW and 45.65 μg∙g^-1 DW, respectively). In petioles, β-carotene was detected only in Huangtaiji, lutein only existed in Jinnan Shiqin and Huangtaiji. The expression level of AgCCD4 was highest in celery leaf blades and lowest in roots, respectively. In leaf blades, the relative expression levels of AgCCD4 in Zigan NO.1 shared similar rhythm change with that Saixue, which were significantly higher than that in others. 【Conclusion】 In this study, AgCCD4 gene was cloned from four celery varieties respectively, while the gene sequence of Saixue was different with other three varieties. AgCCD4 protein contained a RPE65 conserved domain. The expression of AgCCD4 was remarkably varied in different celery tissues and was negatively correlated with the carotenoids content. The content and types of carotenoids affected the plants’ color, and AgCCD4 might regulate the pigmentation of celery tissues by degrading carotenoids.

Development and Application of KASP Molecular Markers of Some Important Traits for Peach

MENG JunRen,ZENG WenFang,DENG Li,PAN Lei,LU ZhenHua,CUI GuoChao,WANG ZhiQiang,NIU Liang

Scientia Agricultura Sinica. 2021, 54(15):  3295-3307.  doi:10.3864/j.issn.0578-1752.2021.15.013

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【Objective】 In order to improve breeding efficiency based on the marker-assisted selection in peach, a series of high-throughput and low-cost KASP markers for important traits (such as fruit skin fuzz, fruit shape, stony hard fruit texture, DBF blood-flesh and resistance to green peach aphids) of peach were developed. 【Method】 Based on the resequenced genome information of some peach cultivars, multiple sequence alignment was used to find specific SNP within 300 kb of both flanks of target genes or loci for related traits. KASP markers were developed according to the differences of SNPs, and the close link between KASP markers and the target characteristics was confirmed by genotyping.【Result】 The developed KASP molecular markers for five traits were utilized to detect the genotypes of peach hybrid populations and natural populations. The results showed that the markers identification was completely consistent with the known phenotypes, and the accuracy was 100%. In the hybrid populations of CN20 × 01-77-4, the segregation ratio of peach peel with fuzz/without fuzz, flat fruit/round fruit, and the segregation ratio of resistance to green peach aphids/susceptibility was 30﹕30, 31﹕29, and 49﹕46, respectively, which were in accordance with the 1﹕1 of Mendel’s first law. In population of CN20 × 10 xin 25-8, the high-throughput KASP molecular marker was used to detect genotypes of 53 offspring, and the results showed that genotypes of 27 were G/G appeared stony hard peach and 21 were T/C appeared DBF blood-flesh fruit, which were consistent with the phenotype identification results.【Conclusion】 The KASP marker could be efficiently used to detect allelic variations of genes related to important traits, such as peach fruit appearance, resistance, and fruit texture. It had a good application prospect in genotypic identification, parents apolegamy and hybrid progenies marker-assisted selection.

Fine Mapping of an Immature Rind Color Gene GR in Melon

XU XinYang,SHEN Jia,ZHANG YueJian,LI GuoJing,NIU XiaoWei,SHOU WeiSong

Scientia Agricultura Sinica. 2021, 54(15):  3308-3319.  doi:10.3864/j.issn.0578-1752.2021.15.014

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【Objective】 The aim of this study was to explore the inheritance pattern of immature rind color of melon (Cucumis melo L.), to fine map target gene GR, and to deepen the understanding of rind color change during fruit growth, so as to provide a guidance for the improvement of melon color with molecular design breeding.【Method】 The dark-green rind line ‘MR-1’ (C. melo ssp. agrestis) and the light-green rind line ‘LGR’ (C. melo ssp. melo) were used as parents to construct the F₁ hybrid population, and the BC₁F₁ backcross population was constructed from crossing by F₁ and ‘LGR’ for genetic analysis of immature rind color. By selecting 20 dark-green and light-green plants each in BC₁F₁ population, the DNA was mixed, respectively, and the BSA-seq was operated for initial mapping. Based on the resequencing of two parents, the molecular markers with better specificity were developed in the initial region and recombinant individuals were identified and selected to verify and narrow the interval for fine mapping the GR gene. By sequencing of coding regions between two parents according to the gene annotation, the candidate gene and key variant site were determined. Moreover, the phenotype of immature and mature fruit in the BC₁F₁ backcross population was investigated and assessed by correlation analysis to explore the underlying mechanism of rind color transition in the fruit development.【Result】 According to the investigation, the phenotype of all F₁ individual plants exhibited dark-green rind color. In addition, the immature rind color of BC₁F₁ backcross population was found to be separated, and the ratio of the number of dark-green to light-green was approximately 1﹕1. As well as, the ratio of the number of dark-green to light-green in the F₂ population was 3﹕1. These ratios corresponded to Mendel’s law of inheritance, indicating that the immature rind color of melon was a quality trait, controlled by a single nuclear gene GR, and the dark-green was dominant to light-green. Through BSA-seq, the gene was initially mapped to a 1.8 Mb interval on the long arm of chromosome 4. With developed molecular markers, 24 recombinant individuals were selected in expanded mapping population. The gene was further narrowed down to a region between markers 4-102 and 4-81 with a physical distance of 17.7 kb by genotype and phenotype verification of offspring, where were four predicted genes with latest annotation. Sequencing analysis revealed that a gene MELO3C003375 encoding GLKs transcription factor CmAPRR2 had several variations in ‘MR-1’ and ‘LGR’. Among them, there were three synonymous, a missense mutation, and a nonsense mutation. The nonsense mutation (G to T) appeared in the 856th base of the coding region led to premature translation termination and most of the Myb-DNA binding domain to be lost in ‘LGR’. Thus, the MELO3C003375 (CmAPRR2) was speculated to be the GR gene and the nonsense mutation was the key variation that affected the immature rind color of melon. It was found that there was a significant correlation between the rind color of immature fruit and mature fruit by investigating the phenotype of fruits in the BC₁F₁ backcross population.【Conclusion】 Immature rind color (dark green/light green) of melon was a quality trait and controlled by a single nuclear gene GR. By mapping, MELO3C003375 (CmAPRR2) was presumed to be the candidate gene that affected immature rind color.

FOOD SCIENCE AND ENGINEERING

The Mechanism of Myofibrillar Protein Gel Functionality Influenced by Modified Sugarcane Dietary Fiber

ZHUANG XinBo,CHEN YinJi,ZHOU GuangHong

Scientia Agricultura Sinica. 2021, 54(15):  3320-3330.  doi:10.3864/j.issn.0578-1752.2021.15.015

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【Objective】 The relationships between the myofibrillar protein gel networks, the spatial distribution of dietary fiber and protein, and the textural property of composite gel were investigated in present study. The aim of this study was to expound the mechanism of myofibrillar protein gel influenced by modified sugarcane dietary fiber (SDF), so as to provide a theoretical basis for the application of sugarcane dietary fiber as fat replacement in low-fat sausage. 【Method】 The present study modified the physicochemical properties of sugarcane dietary fiber by hydrogen peroxide treatment. The myofibrillar protein with various concentrations and particle sizes of sugarcane dietary fiber were set as the model system. The treatment without SDF was the control; the treatment with 1%, 2% and 3% 50-mesh SDF addition respectively named T150, T250 and T350; the treatment with 1%, 2% and 3% 100-mesh SDF addition respectively named T100, T200 and T300.The dynamic rheological properties were analyzed by the rheometer; the true fracture stress and strain of composite gels were analyzed by the textural instrument; the spatial distribution of sugarcane dietary fiber in the MP gels were observed by the paraffin section, the microstructure and corresponding image analysis of myofibrillar protein gel networks were analyzed by the SEM and the image analysis software. 【Result】 With the increase of concentrations and particle sizes of sugarcane dietary fiber, the centrifugal loss of composite gel significantly reduced, while the storage module (G') significantly increased. The result showed that the SDF addition significantly increased the fracture stress, while the SDF addition significantly reduced the fracture strain. Paraffin section showed that the sugarcane dietary fiber did not directly interact with protein. The dietary fiber just simply trapped in the protein networks and formed numerous various shapes and volumes cavities. The SEM showed that the myofibrillar protein networks under the control were filled with the connected moisture channels, and the existing of the moisture channel seriously hindered the interaction of the hydrophobic groupings, leading to the loose networks. The dietary fiber addition reduced the cross-linked moisture channels, and promoted the formation of compact and well-aggregated MP gel networks. The image analysis results showed that the treatment T350 had the highest fractal dimension value of 1.8670 and the lowest lacunary value of 0.19.【Conclusion】 The composite gel was comprise of the frame structure formed by the heat-induced gel protein networks and the filled structure formed by the SDF as the filling phase and protein matrix as the continuous phase. The physicochemical properties of SDF proved that the water holding capability was correlated with the particle size. Hence, the treatment with 3% 50-mesh sugarcane dietary fiber could promote the aggregation of myofibrillar protein through moisture stability, and had the highest stress. But the 50-mesh SDF was inelastic structure and formed various shapes and volumes cavities in gel networks, which significantly reduced the strain of composite gel. In conclusion, the 100-mesh SDF (smaller particle size) as fat replacement could significantly increase the stress of composite gel, and ultimately maintain the elasticity of the composite gel.

ANIMAL SCIENCE·VETERINARY SCIENCE·RESOURCE INSECT

Identification of the Core Promoter of Linc-NORFA and Its Transcriptional Regulation in Erhualian Pig

DU Xing,ZENG Qiang,LIU Lu,LI QiQi,YANG Liu,PAN ZengXiang,LI QiFa

Scientia Agricultura Sinica. 2021, 54(15):  3331-3342.  doi:10.3864/j.issn.0578-1752.2021.15.016

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【Objective】 In our previous study, linc-NORFA has been proved as a candidate gene for sow fertility and participated in regulating follicular atresia and granulosa cell apoptosis. The aim of this study is to identify the core promoter of linc-NORFA and investigate its transcriptional regulation in Erhualian pig, so as to provide theoretical basis and new ideas for revealing the mechanism of linc-NORFA regulation to ovarian follicular atresia.【Method】 Ear samples of Euhualian pig were collected for genomic DNA extraction. PCR amplification and clone sequencing were used to obtain the 5’-flanking sequence of Erhualian pig linc-NORFA gene. Reporter vectors construction and luciferase activity assays were performed to identify the core promoter of linc-NORFA gene, and bioinformatic methods were conducted to analyze the characterization of linc-NORFA core promoter and the potential binding elements of transcription factors (TFs). In addition, pig FOXO1 gene eukaryotic expression vector was constructed and Western blot, qRT-PCR, and luciferase activity assays were performed to analyze the effects and regulatory mechanism of FOXO1 overexpression on the transcription of linc-NORFA gene. Besides, chromatin immunoprecipitation (ChIP) assay was performed to identify the interaction between FOXO1 and the core promoter of linc-NORFA in porcine granulosa cells (GCs).【Result】 A total of 1 734 bp 5’-flanking sequence of Erhualian pig linc-NORFA was obtained by PCR amplification and clone sequencing technology, which contained two potential CpG islands. Luciferase activity assay was performed and demonstrated that the core promoter of Erhualian pig linc-NORFA was located at -988 — -684 bp (TSS as +1). Multiple potential binding elements of several transcription factors (TFs) were identified within the core promoter of linc-NORFA using bioinformatic analyses, including ESR2, FOXO1, E2F1, BRCA1 and NFIC. In addition, results from ChIP assay proved that FOXO1 directly binds to the core promoter of linc-NORFA by acting as a transcription factor. Furthermore, It was proved that overexpression of FOXO1 could significantly down-regulate the activity of linc-NORFA core promoter (P<0.01), and also notably inhibited the expression level of linc-NORFA in porcine GCs (P<0.01).【Conclusion】 In this study, the core promoter of Erhualian pig linc-NORFA was identified, and FOXO1 acts as a transcription factor was proved, which significantly inhibited linc-NORFA transcription in porcine GCs through binding and further down-regulating the activity of its core promoter. These findings were of great significance for investigating the molecular mechanism of down-regulation of linc-NORFA during follicular atresia.

ANIMAL SCIENCE·VETERINARY SCIENCE·RESOURCE INSECT

Index System for Quantitative Evaluation of Pasture Degradation in Meadow Grassland of Inner Mongolia

YAN RuiRui, GAO Wa, SHEN BeiBei, ZHANG Yu, WANG Miao, ZHU XiaoYu, XIN XiaoPing

Scientia Agricultura Sinica. 2021, 54(15):  3343-3354.  doi:10.3864/j.issn.0578-1752.2021.15.017

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【Background】 Inner Mongolia grassland is an important natural ecological barrier in northern China, among which meadow steppe is located in the transition zone from forest to grassland, and it is a very valuable natural renewable resource in China. The proportion of meadow grassland in Inner Mongolia is the largest in China, most of which are pastures. Grazing is one of the most important ways for human beings to affect grassland ecosystem. Excessive grazing will lead to retrograde succession of grassland community, and grassland production performance will be continuously reduced, thus limiting the stable development of grassland animal husbandry. 【Objective】 Comprehensive, accurate and timely assessment of pasture degradation is of great significance for maintaining and promoting sustainable grassland utilization. 【Method】 In this study, the degradation succession law and driving mechanism of grassland pasture were summarized, and the degradation index system of grassland pasture in Inner Mongolia was established by using analytic hierarchy process (AHP), expert investigation and comparative matrix analysis methods, which included 8 indexes, such as aboveground biomass, coverage, average height, plant species, litter, proportion of degradation indicator plant, soil organic carbon content and soil bulk density. Based on the establishment of the comprehensive evaluation index model, the parameters of the reference index were put forward, and the comprehensive index of quantitative evaluation was used to reflect the overall situation of grassland degradation. At the same time, the quantitative evaluation index system of grassland degradation in Inner Mongolia and its technical method were discussed and studied. This method was evaluated and verified based on the controlled grazing experiment in Xeltala of Hulunbuir. 【Result】 The results showed that the weight of the eight indexes from the largest to the smallest in the evaluation index system of Inner Mongolia meadow steppe were aboveground biomass, coverage, average height, proportion of degraded plants, number of plant species, litter, soil organic carbon content, and proportion of soil bulk density increase. Meadow grassland degradation could be classified into four grades: non-degradation, mild degradation, moderate degradation and severe degradation. When the grazing was equal to zero or very light grazing, the grassland belonged to the scope of non-degraded grassland. When the grazing rate was above 90%, the grassland belonged to the range of severely degraded grassland. 【Conclusion】 It was suggested that a longer period of discussion should be carried out in the future research to further improve and update the benchmark reference value, which was conducive to the improvement and maturity of the evaluation index system of pasture degradation, and could provide a basis for quantitative assessment of pasture degradation.

RESEARCH NOTES

Fluorescence Characteristics Study of Nitrogen in Alleviating Premature Senescence of Spring Wheat at High Temperature After Anthesis

JIAN TianCai,WU HongLiang,KANG JianHong,LI Xin,LIU GenHong,CHEN Zhuo,GAO Di

Scientia Agricultura Sinica. 2021, 54(15):  3355-3368.  doi:10.3864/j.issn.0578-1752.2021.15.018

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【Objective】 The aim of this study was to investigate the influence mechanism of nitrogen on the fluorescence characteristics of spring wheat under high temperature, and to clarify the internal mechanism of nitrogen regulation of light reaction center, so as to formulate the nitrogen fertilizer operation measures to alleviate the harm of high temperature.【Method】 The experiment was carried out in 2019 and 2020, using the split-plot trial design. The main zones were 5 nitrogen application, including 0 (N0), 75 kg·hm^-2(N1), 150 kg·hm^-2(N2), 225 kg·hm^-2 (N3), and 300 kg·hm^-2(N4), and the sub-zones were temperatures of 25℃±2℃ (CK) and 35℃±2℃(HT). The interrelationships between nitrogen application and leaf nitrogen content, chlorophyll, PSⅡreaction center activity parameters, PSⅡJ phase variable fluorescence (V_J), PSⅡenergy allocation rate, PI, F_v/F₀, and F_v/F_m at high post-flower temperatures were analyzed. 【Result】 The results showed that the effects of nitrogen application and temperature on leaf nitrogen, chlorophyll a, chlorophyll b, ABS/RC, DI₀/RC, V_J, φE₀ and φD₀ and yield were significant. With the increase of nitrogen application, the yield increased first and then decreased, and reached at the highest yield under N3 with normal and high temperature treatments, which was 9.03 t·hm^-2(CK) and 8.37 t·hm^-2(HT). The difference between high temperature and normal temperature was obvious under different temperature treatment with the same nitrogen application, and the chlorophyll a, ABS/RC, ET₀/RC, TR₀/RC, PI, F_v/F₀, F_v/F_m and yield decreased after high temperature treatment, which indicated that the effects of high temperature on fluorescence parameters and PSⅡactivity had negative effect. Under the treatments of different nitrogen application at the same temperature, the chlorophyll content and ABS/RC, ET₀/RC, PI, F_v/F₀, F_v/F_m of spring wheat increased first and then decreased, while the DI₀/RC and V_J decreased first and then increased, and reached the peak at N3(225 kg·hm^-2), indicating that the effects of nitrogen application on chlorophyll fluorescence parameters and PSⅡactivity had compensatory effect, and the appropriate nitrogen application amount could effectively enhance its activity. The effects of temperature on ABS/RC, TR₀/RC, ET₀/RC, F_v/F₀ and F_v/F_m was not significant, but the interaction between nitrogen application and temperature reached significant level (P<0.05) and extremely significant level (P<0.01). 【Conclusion】 To sum up, the effects of nitrogen application and temperature on the fluorescence characteristics and yield of spring wheat was interactive, in which the dominant factor was temperature, while the amount of nitrogen application had a compensatory effect on it. A reasonable amount of nitrogen application could effectively increase the nitrogen content, chlorophyll content and PSⅡreaction center activity of wheat flag leaves, increase the capture, absorption, transformation and maximum photochemical efficiency of light energy by plants, and reduce the energy dissipation rate, so as to resist the damage caused by high temperature stress to the photosynthetic system of spring wheat. According to this test condition, the nitrogen application amount of N3 could effectively resist high temperature stress and increase the yield of spring wheat. The yield of high spring wheat could provide theoretical basis and technical support for high and stable yield of local spring wheat.