2020 Vol. 19 No. 4 Previous Issue    Next Issue

    Special Focus: Bleeding canker of pear-An emerging devastating disease
    Crop Science
    Animal Science · Veterinary Medicine
    Agro-ecosystem & Environment
    Agricultural Economics and Management

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    Special Focus: Bleeding canker of pear-An emerging devastating disease
    Editorial- Bleeding canker of pear - An emerging devastating disease
    CHEN Gong-you
    2020, 19(4): 887-888.  DOI: 10.1016/S2095-3119(20)63173-2
    Abstract ( )   PDF in ScienceDirect  
    Bleeding canker (BC) of pear trees, is a devastating disease in China.  The disease was originally observed in Jiangsu Province and its causal agent was identified first as Erwinia sp. in the early 1970’s and latter as a novel species, Dickeya fangzhongdai.  BC is epidemically emerging prevalently from April to September annually in pear-growing regions in Zhejiang, Anhui and Shandong provinces, and threatening pear industry currently in China.  To better control BC disease, it is crucial to know BC symptomatology, epidemics, etiology, and diagnostics first.  The special topic of the three papers have well illustrated the points mentioned above.
    The first article by Chen et al. (2020b) described in detail the symptomatology, etiology and epidemiology of BC disease.  BC mainly damages pear trunks and branches with no obvious symptoms early and bacterial rusty oozes mixed with tree saps exuded from died tissues later.  The diseased portions display small soft and sap-filled brown spots or red streaks with strong smells likely of yeast fermentation.  Importantly in this paper, the causal agent is identified as D. fangzhongdai in memory of Prof. Fang Zhongda who was a worldwide distinguished phytopathologist at the Nanjing Agricultural University, China.  The pathogen infects not only pear, but also potato, cabbage, tomato and butterfly orchid, and its virulence is stronger than D.?solani on potato, implying the quarantine is necessary.
    Since early symptoms of BC are inconspicuous and the isolation of the pathogen from infected trees is time-consuming, the second paper (Tian et al. 2020) developed a TaqMan real-time PCR technique to determine D. fangzhongdai using specific primers basing on an elongation factor G (fusA) gene of the pathogen.  Efficiently, 0.2 pg µL–1 DNA and 1×103 CFU mL–1 of the bacterium on asymptomatic trees can be detected by this technique, facilitating early and accurate diagnosis of BC five days before visible symptoms appear.
    Species in Dickeya genus are originally separated from Pectobacterium and Brenneria.  Some Dickeya speices not only cause diseases in herbal plants, but also exist naturally in lakes or rivers.  To distinguish D. fangzhongdai from other Dickeya speices, the third article (Chen et al. 2020a) reported the genome sequences of three isolates of D. fangzhongdai and compared them with other Dickeya genomes available in NCBI database.  Phylogenetic analysis showed three D. fangzhongdai strains are clustered in one branch, obviously different from other seven Dickeya speices.  Genetic differences are observed in D. fangzhongdai strains in some pathogenicity factors, like type III secretion system (T3SS), T3SS-secreted effector (T3SE), type IV secretion system (T4SS), type IV pili (TFPs), plant cell wall degradation enzymes (PCWDE), and membrane transport proteins, which make the pathogen unique.  Interestingly, the TFP deletion makes D. fangzhongdai lose twitching motility and reduce biofilm formation and virulence in pear.
    The findings in the papers enrich our knowledge on how epidemic is the BC disease, what is the pathogen, what tools can be used for BC diagnosis, what are pathogenic and phylogenetic differences of the pathogen from other Dickeya species which can be employed for further quarantine detection.  Believably, the D. fangzhongdai–pear pathosystem set in the reports provides a platform not only for understanding bacterial pathogenicity in the host, but also for developing new technical tools to control BC disease in agriculture. 
    Bleeding canker of pears caused by Dickeya fangzhongdai: Symptoms, etiology and biology
    CHEN Bin, TIAN Yan-li, ZHAO Yu-qiang, WANG Jia-nan, XU Zhi-gang, LI Xiang, HU Bai-shi
    2020, 19(4): 889-897.  DOI: 10.1016/S2095-3119(19)62882-0
    Abstract ( )   PDF in ScienceDirect  

    Bleeding canker, a devastating disease of pear trees (Pyrus pyrifolia L.), was first reported in the 1970s in Jiangsu, China and more recently in other provinces in China.  Trees infected with bleeding canker pathogen, Dickeya fangzhongdai, develop cankers on the trunks and branches, and a rust-colored mixture of bacterial ooze and tree sap could be seen all over the trunks and branches.  In this study, we provided detail descriptions of the symptoms and epidemiology of bleeding canker disease.  Based on pathogenic and phenotypic characterizations, we identified the causal agent of bleeding canker of pear as D. fangzhongdaiDickeya fangzhongdai strains isolated from pear were also pathogenic on Solanum tuberosum, Brassica pekinensis, Lycopersicon esculentum, and Phalaenopsis aphrodite based on artificial inoculation, and the pathogen were more virulent on potato than that of D. solani strain.  This study provides new information about this disease and bleeding canker disease of pear.

    Real-time PCR assay for detection of Dickeya fangzhongdai causing bleeding canker of pear disease in China
    TIAN Yan-li, ZHAO Yu-qiang, CHEN Bao-hui, CHEN Shuo, ZENG Rong, HU Bai-shi, LI Xiang
    2020, 19(4): 898-905.  DOI: 10.1016/S2095-3119(19)62881-9
    Abstract ( )   PDF in ScienceDirect  
    Bleeding canker, caused by Dickeya fangzhongdai, is a devastating disease of pear in China.  The bacterium causes cankers, branch die-back, and eventually kills pear trees.  The typical sign of bleeding canker infection is a rusty-brown bacterial ooze that exudes down from cankers onto branches or trunks.  However, early symptoms and signs are inconspicuous, which makes effective disease management difficult.  Detection and identification of D. fangzhongdai are time-consuming and difficult because no rapid method exists to date.  In this study, a TaqMan real-time PCR assay was developed for D. fangzhongdai based on an elongation factor G (fusA) gene.  The real-time PCR assay detected 0.2 pg µL–1 DNA and 1×103 cfu mL–1 of D. fangzhongdai.  Based on this assay, bleeding canker on asymptomatic pear trees can be diagnosed as early as 5 days after infection.  The real-time PCR assay can facilitate disease management by providing early and accurate diagnosis of the bleeding canker disease of pear.
    Genomic characteristics of Dickeya fangzhongdai isolates from pear and the function of type IV pili in the chromosome
    CHEN Bin, TIAN Yan-li, ZHAO Yu-qiang, WANG Yuan-jie, CHUAN Jia-cheng, LI Xiang, HU Bai-shi
    2020, 19(4): 906-920.  DOI: 10.1016/S2095-3119(19)62883-2
    Abstract ( )   PDF in ScienceDirect  
    Dickeya fangzhongdai, the causal agent of bleeding canker of pear, is a new member of the Dickeya genus and the only one that infects woody plants.  Recent studies have reclassified several Dickeya isolates as D. fangzhongdai, which were isolated from various environments, including water, Phalaenopsis sp. and Aglaonema sp.  To provide genomic characterization of D. fangzhongdai isolates from pear, the genomes of D. fangzhongdai strain JS5 (=China General Microbiological Culture Collection Center, CGMCC 1.15464T=DSM 101947T), along with two other isolates, LN1 and QZH3, were sequenced and compared to those of other Dickeya spp.  Homology greater than 99% was observed among three D. fangzhongdai strains.  Plasmid, type IV secretion system (T4SS) and type IV pili (TFPs) were found in genomes of D. fangzhongdai isolates.  Comparative analysis of the type III secretion systems (T3SS), type III secretion effectors (T3SE), plant cell wall degradation enzymes (PCWDE) and membrane transport proteins of Dickeya spp. showed some differences which might reflect the variations of virulence, phylogenetic and phenotypic characteristics of Dickeya spp.  In addition, deletion mutant of TFP in D. fangzhongdai JS5 showed no twitching motility and reduced virulence and biofilm formation.  The fingdings of the distinctive plasmid, T4SS and TFPs, as well as the differences of T3SE, PCWDE and membrane transport proteins make D. fangzhongdai isolates unique.  These results also suggested that acquisition of virulence genes by horizontal gene transfer might play some role in the genetic variation of D. fangzhongdai.
    Crop Science
    Gene mapping and candidate gene analysis of aberrant-floral spikelet 1 (afs1) in rice (Oryza sativa L.)
    ZHANG Ting, YOU Jing, YU Guo-ling, ZHANG Yi, CHEN Huan, LI Yi-dan, YE Li, YAO Wan-yue, TU Yu-jie, LING Ying-hua, HE Guang-hua, LI Yun-feng
    2020, 19(4): 921-930.  DOI: 10.1016/S2095-3119(19)62847-9
    Abstract ( )   PDF in ScienceDirect  
    The spikelet is a unique inflorescence structure in grasses.  However, the molecular mechanism that regulates its development remains unclear, and we therefore characterize a spikelet mutant of rice (Oryza sativa L.), aberrant-floral spikelet 1 (afs1), which was derived from treatment of Xinong 1B with ethyl methanesulfonate.  In the afs1 mutant, the spikelet developed an additional lemma-like organ alongside the other normally developed floral organs, and the paleae were degenerated to differing degrees with or without normally developed inner floral organs.  Genetic analysis revealed that the afs1 phenotype was controlled by a single recessive gene.  The AFS1 gene was mapped between the insertion/deletion (InDel) marker Indel19 and the simple sequence repeat marker RM16893, with a physical distance of 128.5 kb on chromosome 4.  Using sequence analysis, we identified the deletion of a 5-bp fragment and a transversion from G to A within LOC_Os04g32510/ LAX2, which caused early termination of translation in the afs1 mutant.  These findings suggest that AFS1 may be a new allele of LAX2, and is involved in the development of floral organs by regulating the expression of genes related to their development.  The above results provide a new view on the function of LAX2, which may also regulate the development of spikelets.
    Molecular detection of the powdery mildew resistance genes in winter wheats DH51302 and Shimai 26
    QU Yun-feng, WU Pei-pei, HU Jing-huang, CHEN Yong-xing, SHI Zhan-liang, QIU Dan, LI Ya-hui, ZHANG Hong-jun, ZHOU Yang, YANG Li, LIU Hong-wei, ZHU Tong-quan, LIU Zhi-yong, ZHANG Yan-ming, LI Hong-jie
    2020, 19(4): 931-940.  DOI: 10.1016/S2095-3119(19)62644-4
    Abstract ( )   PDF in ScienceDirect  
    Resistance to powdery mildew is an important trait of interest in many wheat breeding programs.  The information on genes conferring resistance to powdery mildew in wheat cultivars is useful in parental selection.  Winter wheat breeding line DH51302 derived from Liangxing 99 and cultivar Shimai 26 derived from Jimai 22 showed identical infection patterns against 13 isolates of Blumeria graminis f. sp. tritici (Bgt) that causes wheat powdery mildew.  DH51302 and Shimai 26 were crossed to a powdery mildew susceptible cultivar Zhongzuo 9504 and the F2:3 families were used in molecular localization of the resistance genes.  Fourteen polymorphic markers, which were linked to Pm52 from Liangxing 99, were used to establish the genetic linkage maps for the resistance genes PmDH51302 and PmSM26 in DH51302 and Shimai 26, respectively.  These genes were placed in the same genetic interval where Pm52 resides.  Analysis of gene-linked molecular markers indicated that PmDH51302 and PmSM26 differed from other powdery mildew resistance genes on chromosome arm 2BL, such as Pm6, Pm33, Pm51, MlZec1, MlAB10, and Pm64.  Based on the results of reaction patterns to different Bgt isolates and molecular marker localization, together with the pedigree information, DH51302 and Shimai 26 carried the same gene, Pm52, which confers their resistance to powdery mildew.
    Heterologous expression of the ThIPK2 gene enhances drought resistance of common wheat
    ZHANG Shu-juan, LI Yu-lian, SONG Guo-qi, GAO Jie, ZHANG Rong-zhi, LI Wei, CHEN Ming-li, LI Gen-ying
    2020, 19(4): 941-952.  DOI: 10.1016/S2095-3119(19)62714-0
    Abstract ( )   PDF in ScienceDirect  
    ThIPK2 is an inositol polyphosphate kinase gene cloned from Thellungiella halophila that participates in diverse cellular processes.  Drought is a major limiting factor in wheat (Triticum aestivum L.) production.  The present study investigated whether the application of the ThIPK2 gene could increase the drought resistance of transgenic wheat.  The codon-optimized ThIPK2 gene was transferred into common wheat through Agrobacterium-mediated transformation driven by either a constitutive maize ubiquitin promoter or a stress-inducible rd29A promoter from Arabidopsis.  Molecular characterization confirmed the presence of the foreign gene in the transformed plants.  The transgenic expression of ThIPK2 in wheat led to significantly improve drought tolerance compared to that observed in control plants.  Compared to the wild type (WT) plants, the transgenic plants showed higher seed germination rates, better developed root systems, a higher relative water content (RWC) and total soluble sugar content, and less cell membrane damage under drought stress conditions.  The expression profiles showed different expression patterns with the use of different promoters.  The codon-optimized ThIPK2 gene is a candidate gene to enhance wheat drought stress tolerance by genetic engineering.
    Concentration difference of auxin involved in stem development in soybean
    JIANG Zhen-feng, LIU Dan-dan, WANG Tian-qiong, LIANG Xi-long, CUI Yu-hai, LIU Zhi-hua, LI Wen-bin
    2020, 19(4): 953-964.  DOI: 10.1016/S2095-3119(19)62676-6
    Abstract ( )   PDF in ScienceDirect  
    Auxin regulates cell division and elongation of the primordial cells through its concentration and then shaped the plant architecture.  Cell division and elongation form the internode of soybean and result in different plant heights and lodging resistance.  Yet the mechanisms behind are unclear in soybean.  To elucidate the mechanism of the concentration difference of auxin related to stem development in soybean, samples of apical shoot, elongation zone, and mature zone from the developing stems of soybean seedlings, Charleston, were harvested and measured for auxin concentration distributions and metabolites to identify the common underlying mechanisms responsible for concentration difference of auxin.  Distribution of indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), and methylindole-3-acetic acid (Me-IAA) were determined and auxin concentration distributions were found to have a complex regulation mechanism.  The concentrations of IAA and Me-IAA in apical shoot were significantly different between elongation zone and mature zone resulting in an IAA gradient.  Tryptophan dependent pathway from tryptamine directly to IAA or through indole-3-acetonitrile to IAA and from indole-3-propionic acid (IPA) to IAA were three primary IAA synthesis pathways.  Moreover, some plant metabolites from flavonoid and phenylpropanoid synthesis pathways showed similar or reverse gradient and should involve in auxin homeostasis and concentration difference.  All the data give the first insight in the concentration difference and homeostasis of auxin in soybean seedlings and facilitate a deeper understanding of the molecular mechanism of stem development and growth.  The gathered information also helps to elucidate how plant height is formed in soybean and what strategy should be adopted to regulate the lodging resistance in soybean.
    Screening of diverse cassava genotypes based on nitrogen uptake efficiency and yield
    KANG Liang, LIANG Qiong-yue, JIANG Qiang, YAO Yi-hua, DONG Meng-meng, HE Bing, GU Ming-hua
    2020, 19(4): 965-974.  DOI: 10.1016/S2095-3119(19)62746-2
    Abstract ( )  
    As one of the top three tuber crops of the world, cassava is a staple food and feed crop for tropical and subtropical regions.  Because of its high drought resistance and tolerance to nutrient deficiency, cassava is usually cultivated on hilly areas that are nutrient-poor.  Nitrogen (N) is one of the significant factors affecting cassava yield.  A double factorial (N level×genotypes) split-plot field experiment was conducted to analyze differences in yield and N accumulation of 25 cassava genotypes under low-N conditions to screen for cassava genotypes with high-N efficiency.  The two-year field experiment showed that cassava yield and N accumulation are determined by specific genotypes, soil N levels, and year.  Among these factors, soil N levels are the main factors that are responsible for differences in cassava yield.  When yield and relative N accumulation under low-N conditions were used as screening markers, we identified an efficient and responsive genotype (SC10), and two inefficient and non-responsive genotypes (SC205 and GR5).  The efficient and responsive genotype and the inefficient and non-responsive genotype can be used as study materials to further reveal the mechanisms for high-N efficiency in cassava.
    Application of brassinolide alleviates cold stress at the booting stage of rice
    WANG Shi-qiang, ZHAO Hai-hong, ZHAO Li-ming, GU Chun-mei, NA Yong-guang, XIE Bao-sheng, CHENG Shi-hua, PAN Guo-jun
    2020, 19(4): 975-987.  DOI: 10.1016/S2095-3119(19)62639-0
    Abstract ( )   PDF in ScienceDirect  
    The objective of the study was to determine the physiological mechanisms of plants in response to brassinolide (BR) alleviating cold water stress on rice.  In this study, physiological responses of rice to exogenous BR and cold water submergence were investigated using the chilling-tolerant cultivar Kongyu 131 (KY131) and the chilling-sensitive cultivar Kenjiandao 6 (KJD6).  A total of 2 mg L–1 BR increased activities of superoxide dismutase (SOD) and peroxidase (POD) and the contents of soluble sugar, soluble protein, and chlorophyll, but decreased the malondialdehyde (MDA) content in KY131 and KJD6 under cold water stress.  The observed decreases in SOD and POD activities and MDA content recovered quickly after plants were returned to irrigation with water at temperatures of about 23.0°C in 2014.  Additionally, the contents of nitrogen (N), phosphorous (P), and potassium (K) were increased by BR treatment under cold water stress.  Exposure to BR also raised the percentage of high effective leaf area and leaf area index at the heading stage.  Furthermore, it promoted soluble sugar synthesis, increased the rate of dry matter accumulation, and enhanced the export and translocation rates of the stem-sheath.  The yield in KJD6 was significantly (P≤0.01 and P≤0.05) higher than that of the control in 2013 and 2014, respectively.  The effect of BR treatment on rice leaf SOD and POD activities, MDA, chlorophyll, P, and stem-sheath K contents were more significant in KJD6 than in KY131.  In conclusion, exogenous BR effectively reduced the physiological and metabolic damage in rice due to cold stress at the booting stage, promoted functional recovery in plants that received irrigation with water at a normal temperature following cold stress, and mitigated the effects of cold water stress on yield.  The two varieties exhibited differential responses to BR; the weaker cold-resistant variety was more sensitive to BR and displayed stronger responses to exogenous BR.
    Characterization of eating quality and starch properties of two Wx alleles japonica rice cultivars under different nitrogen treatments
    HUANG Shuang-jie, ZHAO Chun-fang, ZHU Zhen, ZHOU Li-hui, ZHENG Qing-huan, WANG Cai-lin
    2020, 19(4): 988-998.  DOI: 10.1016/S2095-3119(19)62672-9
    Abstract ( )   PDF in ScienceDirect  
    To understand the effect of nitrogen (N) fertilizer on rice (Oryza sativa L.) eating and cooking quality (ECQ).  Here, we investigated the ECQ attributes, physicochemical foundation of ECQ, and amylopectin fine structure of two Waxy (Wx) alleles japonica rice cultivars Nanjing 9108 (NJ9108) and Huaidao 5 (HD5) under four N rates (0, 150, 300, and 450 kg ha–1).  Sensory and pasting properties of the two cultivars varied depending on N rates.  Compared with the control (0 kg ha–1), the overall eating quality and sensory value were significantly decreased under the N rates of 300 and 450 kg ha–1.  Further, conventional descriptive analysis showed that the stickiness and retrogradation of cooked rice were significantly decreased.  These results indicated that application of N fertilizer seems to affect the texture of cooked rice, causing it to be less sticky, lowering its retrogradation, and consequently reducing its palatability.  Results from rapid visco analyzer (RVA) revealed that the peak and breakdown viscosities significantly decreased, while the setback viscosity and peak time increased under the N rates of 300 and 450 kg ha–1.  However, no significant difference was observed when the N rate was 150 kg ha–1, indicating that less N fertilization can maintain rice ECQ.  As the N rate increasing, protein content increased, whereas apparent amylose content, starch content, and gel consistency almost unchanged.  Interestingly, compared with the control, under N treatments, the percentage of short amylopectin branches in NJ9108 was decreased, but increased in HD5, as controlled by amylopectin synthesis-related genes.  Notably, SSI and BEIIb were down-regulated in NJ9108, whereas BEIIb was up-regulated in HD5.  Thus, the palatability of both rice cultivars was significantly decreased under excessive N fertilization as a consequence of reduced stickiness and retrogradation of the cooked rice, which might have resulted from an elevated protein content and altered amylopectin fine structure.  In addition, amylopectin synthesis appeared to be affected by N fertilizer and the genotype of the rice cultivar.
    Comparative analysis on grain quality and yield of different panicle weight indica-japonica hybrid rice (Oryza sativa L.) cultivars
    BIAN Jin-long, REN Gao-lei, HAN Chao, XU Fang-fu, QIU Shi, TANG Jia-hua, ZHANG Hong-cheng, WEI Hai-yan, GAO Hui
    2020, 19(4): 999-1009.  DOI: 10.1016/S2095-3119(19)62798-X
    Abstract ( )   PDF in ScienceDirect  
    Indica-japonica hybrid rice (Oryza sativa L.) cultivars showed high yield potential and poor tasting quality when compared with common japonica rice cultivars.  Large panicle is a prominent factor of high yield for indica-japonica hybrid rice cultivars, and the panicle weight varies greatly among different indica-japonica hybrid rice cultivars.  It is important to research on yield and grain quality of different panicle weight indica-japonica hybrid rice cultivars.  In this study, two different panicle types indica-japonica hybrid cultivars were used to research on the relation of yield and grain quality.  The yields of two heavy panicle weights indica-japonica hybrid cultivars were significantly higher than that of two medium panicle weight rice cultivars.  The cooking and eating quality and starch properties of different panicle type cultivars were evaluated.  Yongyou 6715 (medium panicle) and Yongyou 1852 (heavy panicle) got the relatively higher cooking and eating quality.  Rice cultivars with medium panicle weight had more large starch granules and higher relative crystallinity than cultivars with heavy panicle weight.  Transition temperature and retrogradation enthalpy (ΔHret) of medium panicle type cultivars were significantly higher than that of heavy panicle type cultivars.  There was no significant difference in amylose content among different panicle type cultivars.  Protein content of heavy panicle type cultivar was higher than that of medium panicle type cultivar, and protein content is the main factor affect cooking and eating quality in this study.  The cultivar Yongyou 6715 got the highest taste value with the lowest protein content.  Thus, it is suggested that the emphasis on improving rice cooking and eating quality of indica-japonica hybrid rice cultivars is how to reduce the protein content in rice grain.  According to the results of this study, medium panicle type with high grain weight is the desired panicle type for high quality indica-japonica hybrid rice breeding.
    Effects of sodium benzoate on growth and physiological characteristics of wheat seedlings under compound heavy metal stress
    LIANG Pan-pan, ZHAO Chen, LIN Yuan, GENG Ji-jia, CHEN Yuan, CHEN De-hua, ZHANG Xiang
    2020, 19(4): 1010-1018.  DOI: 10.1016/S2095-3119(19)62723-1
    Abstract ( )   PDF in ScienceDirect  
    In this study, we investigated the effect of exogenous sodium benzoate on wheat seedlings (Yangmai 16) grown under heavy metal stress.  The results showed that 2.4 mmol kg–1 of heavy metals significantly inhibited growth and delayed emergence of wheat seedlings.  Under compound heavy metal stress, application of 2–4 g L–1 sodium benzoate significantly increased (P<0.01) chlorophyll content and chlorophyll fluorescence parameters Fv/Fm and Fv/Fo of wheat, compared to the control (water treatment).  Further analysis showed that application of 2–4 g L–1 sodium benzoate alleviated osmotic stress by promoting the accumulation of osmolytes such as soluble proteins and free proline, increased the activity of superoxide dismutase (SOD) and reduced malondialdehyde content (MDA).  In contrast, higher concentrations of sodium benzoate solution (>6 g L–1) inhibited the growth of wheat seedlings and even caused damage to seedlings.  Correlation analysis showed that when the sodium benzoate concentration was in the range of 1.97–3.12 g L–1 (2016) and 1.58–3.27 g L–1 (2017), values of chlorophyll and its components, root activity, SOD activity, soluble protein, and free proline content were the highest.  When the sodium benzoate concentration was raised to 2.59 g L–1 (2016) or 3.02 g L–1 (2017), MDA content was the lowest.  Ultimately, exogenous sodium benzoate (2–4 g L–1) facilitates root development and improves the root activity of wheat seedlings grown under compound heavy metals stress, thereby effectively alleviating the damage of compound heavy metal stress in wheat seedlings.
    Single-seed sowing increased pod yield at a reduced seeding rate by improving root physiological state of Arachis hypogaea
    LIANG Xiao-yan, GUO Feng, FENG Ye, ZHANG Jia-lei, YANG Sha, MENG Jing-jing, LI Xin-guo, WAN Shu-bo
    2020, 19(4): 1019-1032.  DOI: 10.1016/S2095-3119(19)62712-7
    Abstract ( )   PDF in ScienceDirect  
    Double-seed sowing (two seeds per hole) is the dominant pattern of peanut sowing in China, but within-hole plant competition usually limits their growth and yield formation.  Besides, the traditional double-seed sowing method does not facilitate mechanization during sowing.  The objective of this study was to determine if single-seed sowing at a proper seeding rate yielded better than traditional double-seed sowing pattern and the differences of physiological metabolism of roots.  A field experiment was conducted in two consecutive years to compare pod yields of single-seed sowing at 180 000 (S180), 225 000 (S225), and 270 000 seeds ha–1 (S270) with that of double-seed sowing at 270 000 seeds ha–1 (D270) using a completely randomized block design with four replications.  And the root bleeding sap rate, nutrient content, and the main hormone contents in root bleeding sap were also comparatively investigated.  Although the pod yields of single-seed sowing at the three densities were higher than that of traditional double-seed sowing (D270), S225 yielded better than the other two single-seed sowing treatments (S180 and S270).  The increased pod yield in single-seed sowing at 225 000 seeds ha–1 was mainly due to the higher pod dry weight per plant and harvest index.  The improved pod dry weight and shoot growth had closely relationship with the enhanced root physiological traits such as the increased root bleeding sap rate, content of free amino acids, soluble sugars, K+, Mg2+, Zn2+, and Ca2+ of the individual plant root.  The improved activity of root reductive, nitrate reductase (NR) and ATPase and higher zeatin and zeatin riboside (Z+ZR) content of root bleeding sap were also crucial to the pod and shoot growth of peanut.  Single-seed sowing at a moderate seeding rate (S225) is a potential practice to increase pod yield and to save seed cost.
    The MADS-box transcription factor CmAGL11 modulates somatic embryogenesis in Chinese chestnut (Castanea mollissima Blume)
    GAO Yue-rong, SUN Jia-chen, SUN Zhi-lin, XING Yu, ZHANG Qing, FANG Ke-feng, CAO Qing-qin, QIN Ling
    2020, 19(4): 1033-1043.  DOI: 10.1016/S2095-3119(20)63157-4
    Abstract ( )   PDF in ScienceDirect  
    Somatic embryogenesis (SE) is an effective approach of in vitro regeneration that depends on plant cell totipotency. However, largely unknown of molecular mechanisms of SE in woody plants such as Chinese chestnut (Castanea mollissima Blume), limits the development of the woody plant industry. Here, we report the MADS-box transcription factor CmAGL11 in Chinese chestnut. CmAGL11 transcripts specifically accumulated in the globular embryo. Overexpression of CmAGL11 in chestnut callus enhanced its SE capacity, and the development of somatic embryos occurred significantly faster than in the control. RNA-seq results showed that CmAGL11 affects the expression of several genes related to the gibberellin, auxin, and ethylene pathways. Moreover, the analysis of DNA methylation status indicated that the promoter methylation plays a role in regulation of CmAGL11 expression during SE. Our results demonstrated that CmAGL11 plays an important role in the SE process in Chinese chestnut, possibly by regulating gibberellin, auxin, and ethylene pathways. It will help establish an efficient platform to accelerate genetic improvement and germplasm innovation in Chinese chestnut.
    Response of axillary bud development in garlic (Allium sativum L.) to seed cloves soaked in gibberellic acid (GA3) solution
    LIU Hong-jiu, HUANG Cai-ping, TONG Pei-jiang, YANG Xue, CUI Ming-ming, CHENG Zhi-hui
    2020, 19(4): 1044-1054.  DOI: 10.1016/S2095-3119(20)63156-2
    Abstract ( )   PDF in ScienceDirect  
    Gibberellins (GAs) are important phytohormones that regulate many developmental processes in plants.  Clove, as the reproductive organ of garlic, dramatically affected garlic bulb development.  Considering the potential of gibberellins in plant development and our previous studies, we investigated the effect of soaking two types of seed cloves (seed clove-I: without root/shoot sprouting; seed clove-II: with root/shoot sprouting) in GA3 solution on axillary bud development and examined the effect of soaking seed cloves in GA3 solution on bulb development, phytohormone level and sugar content in this study.Results indicated seed clove types, soaking liquids and their interaction significantly affected the number of cloves per bulb and the rate of single-clove bulb.  Moreover, soaking seed cloves in 1 mmol L–1 GA3 solution for 24 h not only promoted axillary bud formation and secondary plant growth (equal to tillering or branching), but also slightly increased the number of cloves per bulb and changed bulb structure with a low yield and marketable quality.  On the 40th day after GA3 treatment (at axillary bud outgrowth stage), zeatin riboside (ZR) and soluble protein in stem were sharply increased with the increase of GA3, sucrose, fructose and soluble protein in leaf.  However, GA3, indole-3-acetic acid (IAA), soluble sugar and sucrose in stem (3.52 ng g–1 fresh weight (FW), 19.88 ng g–1 FW, 237.3 mg g–1 FW, and 8.24 mg g–1 FW, respectively) were significantly decreased on the 40th day after GA3 treatment, compared to the control of water treatment (5.56 ng g–1 FW, 32.96 ng g–1 FW, 263.6 mg g–1 FW, and 10.37 mg g–1 FW, respectively).  To our knowledge, these novel results indicate seed cloves soaked in GA3 solution promotes axillary bud formation and outgrowth that caused the changes in plant architecture and bulb structure.  Meanwhile, our findings suggest that the level of endogenous plant hormone (GA3, IAA and ZR) cooperates with the content of sugar (sucrose and fructose) in leaf and stem to regulate axillary bud outgrowth in garlic.
    Animal Science · Veterinary Medicine
    Tissue-specific expression and correlation with promoter DNA methylation of the LBP gene in pigs
    CAO Yue, GAO Zhong-cheng, WU Zheng-chang, WANG Hai-fei, BAO Wen-bin
    2020, 19(4): 1055-1064.  DOI: 10.1016/S2095-3119(19)62749-8
    Abstract ( )   PDF in ScienceDirect  
    Lipopolysaccharide binding protein (LBP) is a key factor in the recognition of lipopolysaccharide (LPS) and the initiation of immune response, thus regulating the body’s resistance to pathogenic infection.  To investigate the tissue-specific expression characteristics of the LBP gene and its transcriptional regulation in pigs, we detected LBP expression in different tissues of 35-day-old Meishan weaned piglets, determined LBP core promoter region using bioinformatics prediction combined with dual luciferase activity assay, and finally detected methylation levels by pyrosequencing.  The results showed that LBP expression in the liver tissue was significantly higher (P<0.01) than that in other tissues, followed by the intestinal tissues.  The core promoter region of LBP was located at –500–(–206) bp (chr.17: g.46837534–g.46837828), containing three CpG sites (CpG1, CpG2 and CpG3).  Of the three CpG sites, CpG2 and CpG3 were variously methylated (P<0.01) in different tissues.  Moreover, LBP mRNA levels were negatively correlated (P<0.01) with methylation levels of the CpG2 and CpG3 sites in the YY1 transcription factor binding sequence.  It is speculated that the methylation of CpG2 and CpG3 sites might inhibit YY1 binding to the promoter sequences, thereby regulating the tissue-specific expression of LBP.  This study demonstrated the distinct patterns of LBP expression and promoter methylation in the tissues of Meishan pigs and indicated the potential roles of DNA methylation in regulating LBP expression, which may contribute to further investigations on pig LBP gene expression and function. 
    The CRISPR/Cas9 induces large genomic fragment deletions of MSTN and phenotypic changes in sheep
    DING Yi, ZHOU Shi-wei, DING Qiang, CAI Bei, ZHAO Xiao-e, ZHONG Shu, JIN Miao-han, WANG Xiao-long, MA Bao-hua, CHEN Yu-lin
    2020, 19(4): 1065-1073.  DOI: 10.1016/S2095-3119(19)62853-4
    Abstract ( )   PDF in ScienceDirect  
    The CRISPR/Cas9 system has been extensively used to engineer genetic loci for the generation of knockouts, insertions, and point mutations in animal models.  However, many mutations that have been reported in animals are small insertions or deletions.  This study used the CRISPR/Cas9 system to induce large DNA fragment deletions in MSTN via three guide RNAs in sheep.  This successfully achieved the precise gene editing of the ovine MSTN gene by injecting both Cas9 mRNA and sgRNAs into embryos at the one-cell stage.  Of 10 edited animals, 3 animals (30%) exhibited large genomic fragment deletions (~5 kb).  Furthermore, the body weights of these 3 animals were significantly different (P0<0.0001, P15=0.001, P30=0.005, P60=0.027) between lambs with large deletions and wildtype lambs.  In addition, the edited lambs were also significantly different (P0<0.0001, P15<0.0001, P30=0.002, P60=0.011) compared with wildtype.  These results suggest that the generated MSTN knockout sheep is a reliable and effective animal model for further study.  Furthermore, this method is time- and labor-saving, and efficient for the creation of animal models for agriculture, biology, and medicine.
    Effects of palm fat powder and coated folic acid on growth performance, ruminal fermentation, nutrient digestibility and hepatic fat accumulation of Holstein dairy bulls
    ZHANG Zhen, LIU Qiang, WANG Cong, GUO Gang, HUO Wen-jie, ZHANG Yan-li, PEI Cai-xia, ZHANG Shuan-lin
    2020, 19(4): 1074-1084.  DOI: 10.1016/S2095-3119(19)62752-8
    Abstract ( )   PDF in ScienceDirect  
    This study evaluated the effects of palm fat powder (PFP) and coated folic acid (CFA) on growth performance, ruminal fermentation, nutrient digestibility, microbial enzyme activity, microflora, hepatic lipid content and gene expression in dairy bulls.  Forty-eight Chinese Holstein bulls ((362±12.4) days of age and (483±27.1) kg of body weight (BW)) were assigned to four groups in a completely randomized design with a 2×2 factorial arrangements.  Supplemental PFP (0 or 30 g PFP kg–1 dietary dry matter (DM)) and CFA (0 or 120 mg FA d–1 as CFA) were mixed into the top one-third of a total mixed ration.  The study included a 20-day adaptation period and followed by a 90-day collection period.  The lower (P<0.01) feed conversion ratio with PFP or CFA addition resulted from the constant DM intake and the higher (P<0.05) average daily gain.  The higher (P<0.05) ruminal pH, ether extract digestibility, microbial α-amylase activity, Butyrivibrio fibrisolvens copy, and expression of peroxisome-proliferator-activated receptor α (PPARα) and carnitine palmitoyl transferase-1 (CPT1), and lower ruminal total volatile fatty acids (VFA) concentration, acetate to propionate ratio, neutral detergent fibre (NDF) digestibility, copies of total protozoa and Ruminococcus flavefaciens, and expression of sterol regulatory element binding protein-1 (SREBP1) and acetyl-coenzyme A carboxylase α (ACACA) were observed for PFP addition.  Supplementation with CFA increased (P<0.05) ruminal total VFA concentration, acetate to propionate ratio, digestibility of DM, organic matter, crude protein and NDF, activity of cellobiase, pectinase and α-amylase, copies of selected microbial except for total protozoa, as well as expression of PPARα, but decreased (P<0.05) ruminal pH, and expression of SREBP1 and ACACA.  The PFP×CFA interaction (P<0.05) was observed for ammonia N, hepatic TG content, and mRNA expression of CPT1 and FAS.  There had no significant difference in hepatic TG content when CFA was supplemented in the diet without PFP addition, the lower (P=0.001) hepatic TG content was observed when CFA was supplemented in the diet with PFP addition.  The higher (P<0.05) mRNA expression of CPT1, and the lower (P<0.05) mRNA expression of FAS and ammonia N concentration were observed when CFA was supplemented in diet either without or with PFP addition.  The results indicated that supplementation of CFA in PFP diet was more effective on increasing hepatic CPT1 expression, and decreasing ammonia N, hepatic TG content and FAS expression than in diet without PFP.  Supplementation with PFP or CFA improved growth performance of dairy bulls by promoting nutrient utilization, microbial enzyme activity, microflora, and hepatic gene expression.
    Antiviral activity of traditional Chinese medicinal plants Dryopteris crassirhizoma and Morus alba against dengue virus
    Maqsood MARYAM, Kian Keong TE, Fai Chu WONG, Tsun Thai CHAI, Gary K K LOW, Seng Chiew GAN, Hui Yee CHEE
    2020, 19(4): 1085-1096.  DOI: 10.1016/S2095-3119(19)62820- 0
    Abstract ( )   PDF in ScienceDirect  
    Dengue virus (DENV) has emerged as a major virus that is spread by mosquitoes.  Recently, it has spread to more than a hundred nations but continues to lack specific treatable medication.  Many traditional Chinese medicinal (TCM) plants are in practice for dengue fever in dengue endemic regions.  These traditional medicines persevere with treatments, which modern medicines lack.  The study aims to substantiate the anti-dengue potential of some traditional herbs and make them available for further studies to facilitate TCM users.  Twelve TCM plants aqueous extracts were evaluated, which are described as cool herbs used for the diseases with high fever.  Lead plants were established through detailed in vitro foci forming unit reduction analysis (FFURA) against all four serotypes and validated through quantitative real-time RT-PCR (qRT-PCR).  Four plants potentially inhibited the virus in primary phenotypic in vitro evaluation.  Two lead plants Dryopteris crassirhizoma (DC) and Morus alba (MA) were identified with half minimal inhibitory concentration (IC50) 130 and 221 µg mL–1, respectively, while the selectivity indices (SI) were 4.21 and 4.62, respectively.  Lead plants equally inhibited all four serotypes of DENV.  Time-of-addition analysis suggested that, DC was active at later stages of viral replication, whereas MA was active during the early stages and even showed some prophylactic activity.  Liquid chromatography-mass spectrometry (HPLC/MS) analysis revealed presence of flavonoids.  DC and MA are identified as potential anti-dengue plants, active against varied stages of dengue virus replication cycle.  These results may serve as the base knowledge for further investigation on their combined treatments or integrative treatment with western medicines, which may improve the overall anti-dengue activity in future.  
    Agro-ecosystem & Environment
    Effectiveness and longevity of amendments to a cadmium-contaminated soil
    ZHAO Rui, LÜ Yi-zhong, MA Yi-bing, LI Ju-mei
    2020, 19(4): 1097-1104.  DOI: 10.1016/S2095-3119(19)62821-2
    Abstract ( )   PDF in ScienceDirect  
    The effectiveness and longevity of amendments will influence the reduction in cadmium (Cd) bioavailability by in situ remediation techniques.  Different amendments, including red mud (RM), corn straw (CS), rape straw (RS), and their combinations with zinc (Zn) fertilizer, were evaluated based on a long-term field experiment.  It was found that all amendments decreased the concentration of available-Cd (EDTA-Cd and Exch-Cd) in soil and also reduced the Cd content (%) in plants.  The amendments were still effective after eight years, although the effect did decline over time.  The reduction of plant Cd content was 83.5% for red mud plus rape straw (RMRS), 65.3% for red mud plus corn straw (RMCS), 50.9% for RS, 54.0% for RM, and 37.3% for CS in the first few years.  The reduction in plant Cd content was still 17.2% for RMRS after eight years, and RMRS was found to be the most effective treatment for decreasing Cd bioavailability.  This study also explained that why the reduction in plant Cd content declined over time is the change of available Cd content in soil over time, which is important for guiding agricultural practice.  It was concluded that RM, CS, RS, and their combinations with Zn fertilizer as effective amendments can have a profound and lasting positive impact on Cd-contaminated soils.
    Canopy morphological changes and water use efficiency in winter wheat under different irrigation treatments
    ZHAO Hong-xiang, ZHANG Ping, WANG Yuan-yuan, NING Tang-yuan, XU Cai-long, WANG Pu
    2020, 19(4): 1105-1116.  DOI: 10.1016/S2095-3119(19)62750-4
    Abstract ( )   PDF in ScienceDirect  
    Water is a key limiting factor in agriculture.  Water resource shortages have become a serious threat to global food security.  The development of water-saving irrigation techniques based on crop requirements is an important strategy to resolve water scarcity in arid and semi-arid regions.  In this study, field experiments with winter wheat were performed at Wuqiao Experiment Station, China Agricultural University in two growing seasons in 2013–2015 to help develop such techniques.  Three irrigation treatments were tested: no-irrigation (i.e., no water applied after sowing), limited-irrigation (i.e., 60 mm of water applied at jointing), and sufficient-irrigation (i.e., a total of 180 mm of water applied with 60 mm at turning green, jointing and anthesis stages, respectively).  Leaf area index (LAI), light transmittance (LT), leaf angle (LA), transpiration rate (Tr), specific leaf weight, water use efficiency (WUE), and grain yield of winter wheat were measured.  The highest WUE of wheat in the irrigated treatments was found under limited-irrigation and grain yield was only reduced by a small amount in this treatment compared to the sufficient irrigation treatment.  The LAI and LA of wheat plants was lower under limited irrigation than sufficient irrigation, but canopy LT was greater.  Moreover, the specific leaf weight of winter wheat was significantly lower under sufficient than limited irrigation conditions, while the leaf Tr was significantly higher.  Correlation analysis showed that the increased LAI was associated with an increase in the leaf Tr, but the specific leaf weight had the opposite relationship with transpiration.  Optimum WUE occurred over a reasonable range in leaf Tr.  In conclusion, reduced irrigation can optimize wheat canopies and regulate water consumption, with only small reductions in final yield, ultimately leading to higher wheat WUE and water saving in arid and semi-arid regions.
    Effects of sediment load on the abrasion of soil aggregate and hydraulic parameters in experimental overland flow
    WANG Jun-guang, YU Bing, NI Shi-min, GUO Zhong-lu, CAI Chong-fa
    2020, 19(4): 1117-1126.  DOI: 10.1016/S2095-3119(19)62719-X
    Abstract ( )   PDF in ScienceDirect  
    The breakdown of soil aggregates under rainfall and their abrasion in overland flow are important processes in water erosion due to the production of more fine and transportable particles and, the subsequent significant effect on the erosion intensity.  Currently, little is known about the effects of sediment load on the soil aggregate abrasion and the relationship of this abrasion with some related hydraulic parameters.  Here, the potential effects of sediment load on soil aggregate abrasion and hydraulic parameters in overland flow were investigated through a series of experiments in a 3.8-m-long hydraulic flume at the slope gradients of 8.7 and 26.8%, unit flow discharges from 2×10–3 to 6×10–3 m2 s−1, and the sediment concentration from 0 to 110 kg m–3.  All the aggregates from Ultisols developed Quaternary red clay, Central China.  The results indicated that discharge had the most significant (P<0.01) effect on the aggregates abrasion with the contributions of 58.76 and 60.34%, followed by sediment feed rate, with contributions of 39.66 and 34.12% at the slope gradients of 8.7 and 26.8%, respectively.  The abrasion degree of aggregates was found to increase as a power function of the sediment concentration.  Meanwhile, the flow depth, friction factor, and shear stress increased as a power function along with the increase of sediment concentration at different slope gradients and discharges.  Reynolds number was obviously affected by sediment concentration and it decreased as sediment concentration increased.  The ratio of the residual weight to the initial weight of soil aggregates (Wr/Wi) was found to increase as the linear function with an increasing flow depth (P=0.008) or Reynolds number (P=0.002) in the sediment-laden flow.  The Wr/Wi values followed a power function decrease with increasing friction factor or shear stress in the sediment-laden flow, indicating that friction factor is the best hydraulic parameter for prediction of soil aggregate abrasion under different sediment load conditions.  The information regarding the soil aggregate abrasion under various sediment load conditions can facilitate soil process-based erosion modeling.
    Screening and degradation characteristics of a tylosin-degrading strain
    FENG Chang-qing, CHENG Deng-miao, FENG Yao, QI Wei-ning, JIA Zhen-hu, Louise WEAVER, LIU Yuan-wang, LI Zhao-jun
    2020, 19(4): 1127-1136.  DOI: 10.1016/S2095-3119(19)62764-4
    Abstract ( )   PDF in ScienceDirect  
    Antibiotics residues have been accumulating in the environment day by day due to overuse of antibiotics.  Recalcitrant antibiotic residues, such as tylosin (TYL), can cause serious environmental problems, which makes it important to eliminate TYL from the environment.  It is important to eliminate TYL from the environment.  In this study, a strain was isolated and purified from fermentation by-product that came from a TYL production factory.  The TYL degrading strain was identified by its morphology, physiological and biochemical reactions and sequencing the PCR-amplified fragments of its 16S rDNA-coding genes.  The temperature, shaking speed, initial TYL concentration, pH and inoculum sizes were investigated under simulated conditions by using single factor tests.  The results showed that TYL2, a high efficient strain was isolated and was identified as Brevibacillus borstelensis.  The degradation rate of TYL by this strain could reach to 75% with an initial concentration of 25 mg L–1 within 7 days under conditions of 7% B. borstelensis (v/v, 2×108 CFU mL–1) at pH 7.0 and at 35°C.  It is interesting that this strain has a very strong ability to degrade the TYL in natural sewage with the degradation rate of 65% within 7 days.  This result could be helpful for the degradation of TYL and provide guidance for the degradation of other antibiotics.
    Agricultural Economics and Management
    Potato farmers’ preference for agricultural insurance in China: An investigation using the choice experimental method
    HUANG Ze-ying, Alec ZUO, SUN Jun-mao, GUO Yan-zhi
    2020, 19(4): 1137-1148.  DOI: 10.1016/S2095-3119(19)62868-6
    Abstract ( )   PDF in ScienceDirect  
    Potato insurance plays an important role in transferring agricultural risks to promote the potato staple strategy.  Understanding farmers’ real preferences for potato insurance attributes is important to improve the potato insurance.  In this study, a choice experiment was designed with attributes such as peril, minimum compensation ratio for production loss, types of crops covered by insurance, annual premium per mu after subsidy, and complexity of claims procedures.  We constructed a mixed logit model based on a questionnaire survey of 362 potato farmers’ choices of insurance attributes from 24 villages in Dingxi City of Gansu Province using random sampling.  The results show that: (1) farmers prefer agricultural insurance with widely perils including output price drop and input cost risk; (2) farmers who have suffered plant disease and insect and pest damage are willing to pay a high premium for the insurance with a high compensation ratio and several types of crops covered; full-time farmers and large-scale farmers preferred insurance products with low complexity of claims procedures.  Therefore, new potato insurance design could be considered specifically for different farmer groups such as those who had previous disaster experiences, and large- or small-scale farm operations. 
    China’s alfalfa market and imports: Development, trends, and potential impacts of the U.S.–China trade dispute and retaliations
    Qingbin WANG, ZOU Yang
    2020, 19(4): 1149-1158.  DOI: 10.1016/S2095-3119(19)62832-7
    Abstract ( )   PDF in ScienceDirect  
    This study examines the development and trends of China’s alfalfa market and imports, identifies key factors for the rapid increase in China’s alfalfa imports, and discusses potential impacts of the U.S.–China trade dispute and retaliations on the alfalfa markets and trade in both nations.  China’s rapid transition toward larger-scale commercial dairy production, with enhanced feed and cost management as well as quality and safety control, and its limited resources for high-quality alfalfa production are key factors for the dramatic increase in its alfalfa imports, from 19 601 metric tons in 2008 to 1.38 million metric tons (mmt) in 2018.  While the United States dominated China’s alfalfa imports with an average share of 97.01% from 2007 to 2017, the share dropped to 83.76% in 2018 and 63.28% in January 2019 due to the trade dispute and retaliations started in 2018.  China will likely remain a large importer of alfalfa because of both its growing demand and the comparative advantages of imported alfalfa in quality and price, but the imports from the United States will be highly affected by the ongoing trade dispute and negotiations.  China is also expected to make more efforts to reduce its dependence on U.S. alfalfa through increased investment in domestic alfalfa production and identification of alternative sources of alfalfa and other hay imports. 
    How does the arthropod–plant system respond to abrupt and gradual increases in atmospheric CO2?
    ZHENG Xiao-xu, WU Gang
    2020, 19(4): 1159-1161.  DOI: 10.1016/S2095-3119(19)62880-7
    Abstract ( )   PDF in ScienceDirect  
    Global warming caused by elevated carbon dioxide (CO2) is a major environmental and policy issue.  The current global average temperature has been elevated by 1°C since the industrial revolution, and it is likely to reach a temperature increase of 1.5°C between 2030 and 2052 (IPCC 2018).  Human-caused emission of CO2 is responsible for the greenhouse effect and the atmospheric CO2 concentration is higher now than at any other time in the past 500 000 years, and it continues to rise (Lüthi et al. 2008).  Impacts of arthropod–plant interactions on carbon dynamics and the global climate are important but often ignored.  For example, outbreaks of the mountain pine beetle, Dendroctonus ponderosae, in British Columbia during 2000–2020 will cause the release of an estimated 270 Mt carbon and convert the forest from a small carbon sink to a large carbon source (Kurz et al. 2008).   The annual carbon release due to outbreaks of this beetle is almost equivalent to the annual carbon emission from all forest fires occurring in Canada over 1959–1999 (Kurz et al. 2008).
    Most studies of arthropod–plant interactions have focused on the effects of ambient CO2 or abruptly increasing CO2 concentrations.  In general, these studies show that elevated CO2 has a positive direct effect on plant photosynthesis and photosynthate production (Bezemer and Jones 1998; Kim et al. 2015; Andresen et al. 2018; Thomey et al. 2019).  Most scientists expect C3 plants to benefit from this additional CO2 and outcompete C4 species, because the efficiency of C3 photosynthesis increases with increasing CO2 concentration to a far greater extent than it does in C4 photosynthesis (Hovenden and Newton 2018; Reich et al. 2018).  Yan et al. (2020) found that elevated CO2 increased photosynthetic rate, nodule number, yield and total phenolic content of Medicago truncatula.  Dong et al. (2018a) reported that elevated CO2 promoted the yield and nutritional quality of cucumber (Cucumis sativus L.).  After conducting a meta-analysis using 57 articles consisting of 1 015 observations, they found that elevated CO2 increased the concentrations of fructose, glucose, total phenols, and total flavonoids in the edible parts of vegetables by 14.2, 13.2, 8.9, and 45.5%, respectively, but decreased the concentrations of protein and nitrate, by 9.5 and 18.0%, respectively (Dong et al. 2018b).  Robinson et al. (2012) reviewed the evidence from 170 studies and concluded that plant biomass, C:N ratio, total phenolics and flavonoids increase under elevated CO2, while N-based secondary metabolites and plant terpenoid concentrations decrease.  Being an important limiting factor for phytophagous arthropods, changes in foliar C-based secondary metabolites (e.g., condensed tannins and phenolics) and N-based chemicals may have major effects on arthropod performance.
    Numerous studies have found that elevated CO2 indirectly influences arthropod performance via the changes in plant chemical composition (Ge et al. 2010; Xu et al. 2013; Wu 2014; Sun et al. 2018).  Wen et al. (2019) observed a significantly longer larval duration and lower fecundity of Nilaparvata lugens in elevated CO2.  After analyzing 122 studies, Robinson et al. (2012) concluded that elevated CO2 increases arthropod survival, abundance and relative consumption rate, but it reduces fecundity, relative growth rate and adult weight.  Many chewing pests, such as cotton bollworm (Helicoverpa armigera) and gypsy moth, exhibited lower fecundity, consumption rate and finite rate under elevated CO2 (Foss et al. 2013; Liu et al. 2017).  The sucking pests, however, displayed varied responses to elevated CO2.  For example, in aphids, the responses to elevated CO2 in terms of fecundity, development and population growth varied between different species, different hosts or even different genotypes of the same host (Sudderth et al. 2005; Gao et al. 2008; Guo et al. 2013).  The studies documented above indicated that the chewing arthropods and sap feeders employ different strategies in response to elevated CO2
    While it is clear that arthropod–plant interactions are affected by atmospheric CO2 concentrations, it is currently uncertain whether an abrupt increase in CO2 causes similar responses as the gradual increase has been observed since the industrial revolution.  A recent study of Bromus inermis (a perennial grass) and its associated arbuscular mycorrhizal fungi (AMF) shows that abrupt and gradual CO2 change regimes may not elicit the same response (Klironomos et al. 2005).  In a long-term 6-year experiment in which plants were exposed to three CO2 regimes (ambient CO2, gradual increase in CO2, and abrupt increase in CO2) for 21 successive generations, more AMF taxa were lost when CO2 was raised abruptly than when a gradual increase of the same magnitude was implemented.  The abrupt change in CO2 resulted in a significant change in mycorrhizal diversity in the first generation, although little change occurred in subsequent generations.  Species richness of AMF was similar in the gradual and ambient CO2 treatments but was significantly lower in the abrupt CO2 change treatment (Klironomos et al. 2005).  It is not known whether these effects would be similar in an intact field experiment where fungal meta-community dynamics may come into play and mediate any local species extinctions.  A comparable long-term 3-year experiment (Wu et al., unpublished data) investigating impacts of abrupt vs. gradual increases in CO2 on life-history traits of N. lugens feeding on rice over 16 successive generations, indicated that the gradual increase in CO2 treatment can promote the growth and physiological metabolism of N. lugens relative to the abrupt CO2 increase treatment.  So, the effects of abrupt and gradual CO2 change regimes on arthropods, plants and their associated organisms could differ because the changes affecting organisms are initially the greatest for the first subsequent generation in the abrupt regime, while the evolutionary responses of the interacting organisms differ between the two regimes.
    Current generalizations about the effects of increasing atmospheric CO2 on arthropod–plant interactions are mainly based on experiments using the abrupt approach.  However, a major assumption of these approaches has not been tested, i.e., whether a single-step increase in CO2 yields similar responses in arthropod–plant systems as a gradual increase over several decades.  If a sudden increase in CO2 does not yield a response that is similar to a gradual increase of the same magnitude, some of these generalizations could be affected.  Hovenden and Newton (2018) considered that long-term experiments show unexpected plant responses to elevated CO2 concentrations.  Therefore, most current research may overestimate the impact of abrupt changes in CO2 concentrations on the arthropod–plant systems.  We must be cautious when designing experiments and explaining the effects of CO2 concentrations on the arthropod–plant system, because the magnitudes of responses to environmental changes that are significantly more abrupt may be different than those that would occur in nature.  Therefore, other model systems and intact ecosystems should be used to understand how an increase in atmospheric CO2 influences interactions between arthropods and their host plants.