2018 Vol. 17 No. 10 Previous Issue    Next Issue

    Special Focus: Beneficial roles silicon plays in agriculture
    Crop Science
    Plant Protection
    Animal Science · Veterinary Medicine
    Agricultural Economics and Management

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    Special Focus: Beneficial roles silicon plays in agriculture
    Editorial - Beneficial roles silicon plays in agriculture
    LIANG Yong-chao
    2018, 17(10): 2137-2137.  DOI: 10.1016/S2095-3119(18)62081-7
    Abstract ( )   PDF in ScienceDirect  
    Silicon (Si), a second most abundant element in soil, is nonessential but beneficial for higher plants. Silicon addition can result in improved plant growth, yield and quality. Indeed, application of Si fertilizer is a rather common agricultural practice in many countries and regions, especially in Southeast Asian countries. Despite that numerous research outcomes show the beneficial roles Si plays in providing plants resistance and/or tolerance to various forms of abiotic and biotic stress, convincing evidence is still lacking that Si is involved directly in plant physiological and/or biochemical metabolisms. Since a decade ago rapid progress has been made in developing molecular modes of Si uptake, transport and distribution, molecular mechanisms by which Si provides resistance to stressful environments remain poorly understood. Apart from the beneficial roles Si offers in resistance against stressful environments, Si has been proven to play important roles in biogeochemical cycles of carbon and nutrients and carbon bio-sequestration. In this special issue, we selected five papers contributed by Fan et al. (2018), Han et al. (2018), Li et al. (2018), Yan et al. (2018) and Zhang et al. (2018), respectively, as a window to reflect the latest research progress of this field in China. We hope that through this special issue both basic and applied researches on Si in agriculture can be boosted further both in China and abroad.
    Silicon acquisition and accumulation in plant and its significance for agriculture
    YAN Guo-chao, Miroslav Nikolic, YE Mu-jun, XIAO Zhuo-xi, LIANG Yong-chao
    2018, 17(10): 2138-2150.  DOI: 10.1016/S2095-3119(18)62037-4
    Abstract ( )   PDF (583KB) ( )  
    Although silicon (Si) is ubiquitous in soil and plant, evidence is still lacking that Si is essential for higher plants.  However, it has been well documented that Si is beneficial for healthy growth of many plant species.  Si can promote plant mechanical strength, light interception, as well as resistance to various forms of abiotic and biotic stress, thus improving both yield and quality.  Indeed, application of Si fertilizer is a rather common agricultural practice in many countries and regions.  As the beneficial effects provided by Si are closely correlated with Si accumulation level in plant, elucidating the possible mechanisms of Si uptake and transport in plants is extremely important to utilize the Si-induced beneficial effects in plants.  Recently, rapid progress has been made in unveiling molecular mechanisms of Si uptake and transport in plants.  Based on the cooperation of Si influx channels and efflux transporters, a model to decipher Si uptake, transport and distribution system in higher plants has been developed, which involves uptake and radial transport in root, xylem and inter-vascular transport and xylem unloading and deposition in leaf.  In this paper, we overviewed the updated knowledge concerning Si uptake, transport and accumulation and its significance for the major crops of agricultural importance and highlighted the further research needs as well.
    Beneficial effects of silicon on photosynthesis of tomato seedlings under water stress
    ZHANG Yi, SHI Yu, GONG Hai-jun, ZHAO Hai-liang, LI Huan-li, HU Yan-hong, WANG Yi-chao
    2018, 17(10): 2151-2159.  DOI: 10.1016/S2095-3119(18)62038-6
    Abstract ( )   PDF (930KB) ( )  
    Silicon can improve drought tolerance of plants, but the mechanism still remains unclear.  Previous studies have mainly concentrated on silicon-accumulating plants, whereas less work has been conducted in silicon-excluding plants, such as tomato (Solanum lycopersicum L.).  In this study, we investigated the effects of exogenous silicon (2.5 mmol L–1) on the chlorophyll fluorescence and expression of photosynthesis-related genes in tomato seedlings (Zhongza 9) under water stress induced by 10% (w/v) polyethylene glycol (PEG-6000).  The results showed that under water stress, the growth of shoot and root was inhibited, and the chlorophyll and carotenoid concentrations were decreased, while silicon addition improved the plant growth and increased the concentrations of chlorophyll and carotenoid.  Under water sterss, chlorophyll fluorescence parameters such as PSII maximum photochemical efficiency (Fv/Fm), effective quantum efficiency, actual photochemical quantum efficiency (ФPSII), photosynthetic electron transport rate (ETR), and photochemical quenching coefficient (qP) were decreased; while these changes were reversed in the presence of added silicon.  The expressions of some photosynthesis-related genes including PetE, PetF, PsbP, PsbQ, PsbW, and Psb28 were down-regulated under water stress, and exogenous Si could partially up-regulate their expressions.  These results suggest that silicon plays a role in the alleviation of water stress by modulating some photosynthesis-related genes and regulating the photochemical process, and thus promoting photosynthesis.
    Physiological response and phenolic metabolism in tomato (Solanum lycopersicum) mediated by silicon under Ralstonia solanacearum infection
    FAN Xue-ying, LIN Wei-peng, LIU Rui, JIANG Ni-hao, CAI Kun-zheng
    2018, 17(10): 2160-2171.  DOI: 10.1016/S2095-3119(18)62036-2
    Abstract ( )   PDF (878KB) ( )  
    Bacterial wilt, caused by Ralstonia solanacearum (Rs) is a serious soil-borne disease and silicon can enhance tomato resistance against this disease.  However, few studies have focused on the mechanisms of Si-mediated pathogen resistance from the rhizosphere perspective.  In this study, two tomato genotypes, HYT (susceptible) and H7996 (resistant), were used to investigate the effects of silicon application on disease inhibition, root growth, and organic acid content in both roots and root exudates under R. solanacearum infection.  The results showed that Si application significantly suppressed bacterial wilt in HYT, but had no effect in H7996.  Silicon concentrations in roots, stems and leaves of tomato were significantly increased by Si treatment under R. solanacearum inoculation.  In HYT, Si application increased root dry weight by 22.8–51.6% and leaf photosynthesis by 30.6–208.0%, and reduced the concentrations of citric acid in root exudates by 71.4% and in roots by 83.5%.  However, organic acids did not influence R. solanacearum growth.  Results also demonstrated that salicylic acid (SA) content in roots was significantly increased by silicon addition for H7996 and exogenous SA application could reduce bacterial wilt disease index.  Collectively, these results suggest that Si-modulated phenolic compound metabolism in roots or root exudates, especially citric acid and SA, may be a potential mechanism in the amelioration of bacterial wilt disease by Si.
    Effects of silicon amendment on the occurrence of rice insect pests and diseases in a field test
    HAN Yong-qiang, WEN Ji-hui, PENG Zhao-pu, ZHANG De-yong, HOU Mao-lin
    2018, 17(10): 2172-2181.  DOI: 10.1016/S2095-3119(18)62035-0
    Abstract ( )   PDF (1034KB) ( )  
    Rice is one of the most important staple foods for the world population, but it is attacked by a number of destructive pests.  While evidence from greenhouse and laboratory tests has shown that silicon (Si) amendment can confer enhanced resistance to pests in rice, few studies have directly demonstrated the Si-mediated protection from pests in a field situation.  In this study, field plots with silicon amendments at 0, 75, 150 and 300 kg SiO2 ha–1 in early- and late-season rice were employed to evaluate the effects of silicon amendment on the occurrence of major insect pests and diseases and rice yield.  Compared with the control plots without silicon amendment, plant damage by stem borer and leaf folder and population size of planthopper were significantly lower in three to five of the seven monitoring observations in each season in the plots amended with 300 kg SiO2 ha–1.  The disease index of rice blast in the early-season rice was lower in the plots amended with Si at 300 kg SiO2 ha–1 than in the control plots, while Si protection from rice blast in the late-season rice and from rice sheath blight in the early-season rice were not apparent.  An insignificant increase of rice yield by 16.4% (604 kg ha–1) was observed in the plots amended with 300 kg SiO2 ha–1 over the control plots.  Our results indicate that Si amendment at 300 kg SiO2 ha–1 can provide substantial protection from some of the rice pests under field conditions.  These findings support the recommendation of silicon amendment as a key component of integrated management of rice pests.
    Impacts of silicon on biogeochemical cycles of carbon and nutrients in croplands
    LI Zi-chuan, SONG Zhao-liang, YANG Xiao-min, SONG A-lin, YU Chang-xun, WANG Tao, XIA Shaopan, LIANG Yong-chao
    2018, 17(10): 2182-2195.  DOI: 10.1016/S2095-3119(18)62018-0
    Abstract ( )   PDF (1235KB) ( )  
    Crop harvesting and residue removal from croplands often result in imbalanced biogeochemical cycles of carbon and nutrients in croplands, putting forward an austere challenge to sustainable agricultural production.  As a beneficial element, silicon (Si) has multiple eco-physiological functions, which could help crops to acclimatize their unfavorable habitats.  Although many studies have reported that the application of Si can alleviate multiple abiotic and biotic stresses and increase biomass accumulation, the effects of Si on carbon immobilization and nutrients uptake into plants in croplands have not yet been explored.  This review focused on Si-associated regulation of plant carbon accumulation, lignin biosynthesis, and nutrients uptake, which are important for biogeochemical cycles of carbon and nutrients in croplands.  The tradeoff analysis indicates that the supply of bioavailable Si can enhance plant net photosynthetic rate and biomass carbon production (especially root biomass input to soil organic carbon pool), but reduce shoot lignin biosynthesis.  Besides, the application of Si could improve uptake of most nutrients under deficient conditions, but restricts excess uptake when they are supplied in surplus amounts.  Nevertheless, Si application to crops may enhance the uptake of nitrogen and iron when they are supplied in deficient to luxurious amounts, while potassium uptake enhanced by Si application is often involved in alleviating salt stress and inhibiting excess sodium uptake in plants.  More importantly, the amount of Si accumulated in plant positively correlates with nutrients release during the decay of crop biomass, but negatively correlates with straw decomposability due to the reduced lignin synthesis.  The Si-mediated plant growth and litter decomposition collectively suggest that Si cycling in croplands plays important roles in biogeochemical cycles of carbon and nutrients.  Hence, scientific Si management in croplands will be helpful for maintaining sustainable development of agriculture.
    Crop Science
    Rapid and convenient transformation of cotton (Gossypium hirsutum L.) using in planta shoot apex via glyphosate selection
    GUO Wen-fang, Kevin Yueju Wang, WANG Nan, LI Jun, LI Gang-qiang, LIU De-hu
    2018, 17(10): 2196-2203.  DOI: 10.1016/S2095-3119(17)61865-3
    Abstract ( )   PDF (8968KB) ( )  
    Cotton plants are recalcitrant with regards to transformation and induced regeneration.  In the present study, 5-enolpyruvylshikimate-3-phosphate (EPSPS), a glyphosate resistant gene from the bacterium Agrobacterium sp. strain CP4, was introduced into an elite Bt transgenic cotton cultivar with a modified technique involving in planta Agrobacterium-mediated transformation of shoot apex.  Primary transformants were initially screened using a 0.26% glyphosate spray and subsequently by PCR analysis.  Five out of 4 000 transformants from T1 seeds were obtained resulting in an in planta transformation rate of 0.125%.  Four homozygous lines were produced by continuous self-fertilization and both PCR-based selection and glyphosate resistance.  Transgene insertion was analyzed by Southern blot analysis.  Gene transcription and protein expression levels in the transgenic cotton lines were further investigated by RT-PCR, Western blot, and ELISA methods.  Transgenic T3 plants were resistant to as much as 0.4% of glyphosate treatments in field trials.  Our results indicate that the cotton shoot apex transformation technique which is both tissue-culture and genotype-independent would enable the exploitation of transgene technology in different cotton cultivars.  Since this method does not require sterile conditions, the use of specialized growth media or the application of plant hormones, it can be conducted under the greenhouse condition.
    Overexpression of AmDUF1517 enhanced tolerance to salinity, drought, and cold stress in transgenic cotton
    HAO Yu-qiong, LU Guo-qing, WANG Li-hua, WANG Chun-ling, GUO Hui-ming, LI Yi-fei, CHENG Hong-mei
    2018, 17(10): 2204-2214.  DOI: 10.1016/S2095-3119(17)61897-5
    Abstract ( )   PDF (4492KB) ( )  
    As abiotic stresses become more severe as a result of global climate changes, the growth and development of plants are restricted. In the development of agricultural crops with greater stress tolerance, AmDUF1517 had been isolated from the highly stress-tolerant shrub Ammopiptanthus mongolicus, and can significantly enhance stress tolerance when inserted in Arabidopsis thaliana. In this study, we inserted this gene into cotton to analyze its potential for conferring stress tolerance. Two independent transgenic cotton lines were used. Southern blot analyses indicated that AmDUF1517 was integrated into the cotton genome. Physiological analysis demonstrated that AmDUF1517-transgenic cotton had stronger resistance than the control when treated with salt, drought, and cold stresses. Further analysis showed that trans-AmDUF1517 cotton displayed significantly higher antioxidant enzyme (superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione S-transferase (GST)) activity and less reactive oxygen species (ROS) accumulation, which suggests that overexpression of AmDUF1517 can improve cotton resistance to stress by maintaining ROS homeostasis, as well as by alleviating cell membrane injury. These results imply that AmDUF1517 is a candidate gene in improving cotton resistance to abiotic stress. 
    Advances in salinity tolerance of soybean: Genetic diversity, heredity, and gene identification contribute to improving salinity tolerance
    CHEN Hua-tao, LIU Xiao-qing, ZHANG Hong-mei, YUAN Xing-xing, GU He-ping, CUI Xiao-yan, CHEN Xin
    2018, 17(10): 2215-2221.  DOI: 10.1016/S2095-3119(17)61864-1
    Abstract ( )   PDF (725KB) ( )  
    Salt stress is one of the major abiotic stresses affecting soybean growth.  Genetic improvement for salt tolerance is an effective way to protect soybean yield under salt stress conditions.  Successful improvement of salt tolerance in soybean relies on identifying genetic variation that confers tolerance in soybean germplasm and subsequently incorporating these genetic resources into cultivars.  In this review, we summarize the progress in genetic diversity and genetics of salt tolerance in soybean, which includes identifying genetic diversity for salt tolerant germplasm; mapping QTLs conferring salt tolerance; map-based cloning; and conducting genome-wide association study (GWAS) analysis in soybean.  Future research avenues are also discussed, including high throughput phenotyping technology, the CRISPR/Cas9 Genome-Editing System, and genomic selection technology for molecular breeding of salt tolerance.
    Effects of slow or controlled release fertilizer types and fertilization modes on yield and quality of rice
    WEI Hai-yan, CHEN Zhi-feng, XING Zhi-peng, ZHOU Lei, LIU Qiu-yuan, ZHANG Zhen-zhen, JIANG Yan, HU Ya-jie, ZHU Jin-yan, CUI Pei-yuan, DAI Qi-gen, ZHANG Hong-cheng
    2018, 17(10): 2222-2234.  DOI: 10.1016/S2095-3119(18)62052-0
    Abstract ( )   PDF in ScienceDirect  
    There is limited information about the influence of slow or controlled release fertilizer (S/CRF) on rice yield and quality.  In this study, japonica rice cultivar Nanjing 9108 was used to study the effects of three different S/CRFs (polymer-coated urea (PCU), sulfur-coated urea (SCU), and urea formaldehyde (UF)) and two fertilization modes (both S/CRF and common urea (CU) as basal fertilizer, S/CRF as basal and CU as tillering fertilizer) on rice yield and quality.  CU only was applied separately as control (CK).  Results showed that, rice grain yield, chalky kernel rate, chalky area, overall chalkiness, and the content of gliadin, glutenin, and protein, all showed the trends of UF>PCU>SCU within the same fertilization mode, and showed the trends of S/CRF as basal and CU as tillering fertilizer>both S/CRF and CU as basal fertilizer within the same type of S/CRF.  In contrast, the contents of amylose, amylopectin, and starch, as well as taste value, and peak and hot viscosity showed trends of SCU>PCU>UF, and the trends of both S/CRF and CU as basal fertilizer>S/CRF as basal and CU as tillering fertilizer.  Among S/CRF treatments and fertilization modes, taste values of cooked rice were positively correlated with amylose, amylopectin, and starch contents, as well as gel consistency, peak viscosity, hot viscosity, and cool viscosity, while negatively correlated with globulin, gliadin, glutenin, and protein contents.  The types of S/CRF and fertilization modes are important for improving rice yield and quality.  Compared to CK, higher yield and similar quality of rice was achieved with UF as basal and CU as tillering fertilizer, and similar yield with improved appearance and eating and cooking quality of rice was achieved with either both UF and CU as basal fertilizer, or PCU as basal and CU as tillering fertilizer.
    Evaluation and analysis of intraspecific competition in maize: A case study on plant density experiment
    ZHAI Li-chao, XIE Rui-zhi, MING Bo, LI Shao-kun, MA Da-ling
    2018, 17(10): 2235-2244.  DOI: 10.1016/S2095-3119(18)61917-3
    Abstract ( )   PDF (1198KB) ( )  
    Intraspecific competition is a common phenomenon in agricultural production, and maize is one of the most sensitive grass species to intraspecific competition due to its low tillering ability.  This study evaluated and analyzed intraspecific competition in maize, and screened competitive indices that could be used to evaluate intraspecific competition in a maize population.  A 2-year field experiment was conducted using the maize hybrid Zhongdan 2 at 12 plant densities ranging from 1.5 to 18.0 plants (pl) m–2.  The results showed that the response of single-plant grain yield and dry matter at harvest to increased plant density decreased exponentially and that the harvest index decreased linearly.  The response of population-level grain yield to plant density was curvilinear, producing a maximum value at the optimum population density.  However, the yield-density equation agreed well with the Steinhart-Hart equation curves, but not with the quadratic equation curves reported by most previous studies.  Competitive indices are used to evaluate competition in a plant population or plant species.  The present results show that competitive intensity (CI) and absolute severity of competition (ASC) increased with increasing plant density; however, relative yield (RY) and relative reproductive efficiency (RReff) decreased.  The different responses of these indices reflect different aspects of competition.  According to the analysis of CI, ASC, RY, and RReff higher CI and ASC values indicate higher intraspecific competition, whereas higher RY and RReff values indirectly reflect lower intraspecific competition.  These competitive indices evaluate not only the intraspecific competitive intensity under different plant densities of the same cultivar but also those of different cultivars under the same plant density.  However, some overlap exists in the calculations of ASC, CI, and RY, so one could simply select any one of these indices to evaluate intraspecific competition in a maize population.  In conclusion, the present study provides a method to evaluate intraspecific competition in maize populations, which may be beneficial for breeding high-yield maize varieties in the future.   
    Supplemental blue light increases growth and quality of greenhouse pak choi depending on cultivar and supplemental light intensity
    ZHENG Yin-jian, ZHANG Yi-ting, LIU Hou-cheng, LI Ya-min, LIU Ying-liang, HAO Yan-wei, LEI Bing-fu
    2018, 17(10): 2245-2256.  DOI: 10.1016/S2095-3119(18)62064-7
    Abstract ( )   PDF in ScienceDirect  
    To evaluate the supplementary blue light intensity on growth and health-promoting compounds in pak choi (Brassica campestris ssp. chinensis var. communis), four blue light intensity treatments (T0, T50, T100 and T150 indicate 0, 50, 100, and 150 μmol m–2 s–1, respectively) were applied 10 days before harvest under greenhouse conditions.  Both of cultivars (green- and red-leaf pak choi) under T50 had the highest yield, content of chlorophyll and sugars.  With light intensity increasing, antioxidant compounds (vitamin C and carotenoids) significantly increased, while nitrate content showed an opposite trend.  The health-promoting compounds (phenolics, flavonoids, anthocyanins, and glucosinolates) were significantly higher under supplementary light treatment than T0, so as the antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl and ferric-reducing antioxidant power).  The species-specific differences in photosynthetic pigment and health-promoting compounds was found in green- and red-leaf pak choi.  T50 treatment could be used for yield improvement, whereas T100 treatment could be applied for quality improvement.  Results showed that blue light intensity can regulate the accumulation of biomass, morphology and health-promoting compounds in pak choi under greenhouse conditions.
    Exogenous GSH protects tomatoes against salt stress by modulating photosystem II efficiency, absorbed light allocation and H2O2- scavenging system in chloroplasts
    ZHOU Yan, DIAO Ming, CUI Jin-xia, CHEN Xian-jun, WEN Ze-lin, ZHANG Jian-wei, LIU Hui-ying
    2018, 17(10): 2257-2272.  DOI: 10.1016/S2095-3119(18)62068-4
    Abstract ( )   PDF in ScienceDirect  

    The effects of exogenous GSH (reduced glutathione) on photosynthetic characteristics, photosystem II efficiency, absorbed light energy allocation and the H2O2-scavenging system in chloroplasts of salt-stressed tomato (Solanum lycopersicum L.) seedlings were studied using hydroponic experiments in a greenhouse.  Application of exogenous GSH ameliorated saline-induced growth inhibition, the disturbed balance of Na+ and Cl ions and Na+/K+ ratios, and the reduction of the net photosynthetic rate (Pn).  GSH also increased the maximal photochemical efficiency of PSII (Fv/Fm), the electron transport rate (ETR), the photochemical quenching coefficient (qP), and the non-photochemical quenching coefficient (NPQ).  In addition, GSH application increased the photochemical quantum yield (Y(II)) and relative deviation from full balance between the photosystems (β/α–1) and decreased the PSII excitation pressure (1–qP) and quantum yield of non-regulated energy dissipation (Y(NO)) in leaves of salt-stressed tomatoes without BSO (L-buthionine-sulfoximine, an inhibitor of key GSH synthesis enzyme γ-glutamylcysteine synthetase) or with BSO.  Further, the addition of GSH depressed the accumulation of H2O2 and malondialdehyde (MDA), induced the redistribution of absorbed light energy in PSII reaction centers, and improved the endogenous GSH content, GSH/GSSH ratio and activities of H2O2-scavenging enzymes (including superoxidase dismutase (SOD), catalase (CAT), peroxidase (POD) and key enzymes in the AsA-GSH cycle and Grx system) in the chloroplasts of salt-stressed plants with or without BSO.  Therefore, GSH application alleviates inhibition of salt-induced growth and photosynthesis mainly by overcoming stomatal limitations, improving the PSII efficiency, and balancing the uneven distribution of light energy to reduce the risk of ROS generation and to mediate chloroplast redox homeostasis and the antioxidant defense system to protect the chloroplasts from oxidative damage.  Thus, GSH may be used as a potential tool for alleviating salt stress in tomato plants.

    Endogenous nitric oxide and hydrogen peroxide detection in indole- 3-butyric acid-induced adventitious root formation in Camellia sinensis
    WEI Kang, WANG Li-yuan, RUAN Li, ZHANG Cheng-cai, WU Li-yun, LI Hai-lin, CHENG Hao
    2018, 17(10): 2273-2280.  DOI: 10.1016/S2095-3119(18)62059-3
    Abstract ( )   PDF in ScienceDirect  
    Nitric oxide (NO) and hydrogen peroxide (H2O2) are essential signaling molecules with key roles in auxin induced adventitious root formation in many plants.  However, whether they are the sole determinants for adventitious root formation is worth further study.  In this study, endogenous NO and H2O2 were monitored in tea cutting with or without indole-3-butyric acid (IBA) treatment by using the fluorescent probes diaminofluorescein diacetate (DAF-2DA) and 2’,7’-dichlorodihydrofluorescein diacetate (DCF-DA), respectively.  The overproduction of NO and H2O2 was detected in the rooting parts of tea cuttings treated with or without IBA.  But little NO and H2O2 was detected before the initiation phase of tea cuttings even with IBA treatment indicating that they might be not directly induced by IBA.  Further carbon and nitrogen analysis found that the overproduction of NO and H2O2 were coincident with the consumption of soluble sugars and the assimilation of nitrogen.  These results suggest that rooting phases should be taken into consideration with the hypothesis that auxin induces adventitious root formation via NO- and H2O2-dependent pathways and sink establishment might be a prerequisite for NO and H2O2 mediated adventitious root formation. 
    Plant Protection
    Identification, characterization and full-length sequence analysis of a novel endornavirus in common sunflower (Helianthus annuus L.)
    LIU Wen-wen, XIN Min, CAO Meng-ji, QIN Meng, LIU Hui, ZHAO Shou-qi, WANG Xi-feng
    2018, 17(10): 2281-2291.  DOI: 10.1016/S2095-3119(18)61963-X
    Abstract ( )   PDF (15747KB) ( )  
    To identify the possible quarantine viruses in seven common sunflower varieties imported from the United States of America and the Netherlands, we tested total RNAs extracted from the leaf tissues using next-generation sequencing of small RNAs.  After analysis of small RNA sequencing data, no any quarantine virus was found, but a double-stranded RNA (dsRNA) molecule showing typical genomic features of endornavirus was detected in two varieties, X3939 and SH1108.  Full-length sequence and phylogenetic analysis showed that it is a novel endornavirus, temporarily named as Helianthus annuus alphaendornavirus (HaEV).  Its full genome corresponds to a 14 662-bp dsRNA segment, including a 21-nt 5´ untranslated region (UTR), 3´ UTR ending with the unique sequence CCCCCCCC and lacking a poly(A) tail.  An open reading frame (ORF) that encodes a deduced 4 867 amino acids (aa) polyprotein with three domains: RdRP, Hel and UGT (UDP-glycosyltransferase).  HaEV mainly distributed in the cytoplasm but less in the nucleus of leaf cells by fluorescence in situ hybridization (FISH) experiment.  This virus has a high seed infection rate in the five varieties, X3907, X3939, A231, SH1108 and SR1320.  To our knowledge, this is the first report about the virus of the family Endornaviridae in the common sunflower.
    Genetic diversity and population structure of Commelina communis in China based on simple sequence repeat markers
    YANG Juan, YU Hai-yan, LI Xiang-ju, DONG Jin-gao
    2018, 17(10): 2292-2301.  DOI: 10.1016/S2095-3119(18)61906-9
    Abstract ( )   PDF in ScienceDirect  
    Commelina communis (Asiatic dayflower) is a troublesome weed in China.  Genetic variation of 46 C. communis populations from different collection sites in our country was investigated using 12 simple sequence repeat (SSR) primer pairs.  Polymorphism analysis results showed high level of genetic diversity among these populations.  The alleles (bands) were amplified by these primer pairs.  The polymorphic proportion was 18.25%, and the average polymorphism information content was 0.1330.  The highest effective number of alleles was 1.9915 at locus YP33, and the lowest value was 1.0000 at both loci YP25 and YP31.  C. communis showed major average observed heterozygosity value (0.8655) than that of average expected heterozygosity (0.1330).  C. communis populations were divided into three groups on the basis of unweighted pair-group method with arithmetic mean cluster analysis (Dice genetic similarity coefficient=0.772) and genetic structure analysis (K=3), and a principal coordinate analysis.  The results of this study further illustrated that C. communis populations contained abundant genetic information, and the 12 SSR markers could detect the microsatellite loci of C. communis genomic DNA.  These results might indicate that C. communis maintains high genetic diversity among different populations.
    Identifying glyphosate-tolerant maize by soaking seeds in glyphosate solution
    YAN Shu-feng, Sher Muhammad, LIU Hai-fang, TIE Shuang-gui, SUN Shu-ku
    2018, 17(10): 2302-2309.  DOI: 10.1016/S2095-3119(18)61964-1
    Abstract ( )   PDF (2382KB) ( )  
    The identification of glyphosate-tolerant maize genotypes by field spraying with glyphosate is time-consuming, costly and requires treatment of a large area.  We report a potentially better technique of seed-soaking to identify glyphosate-tolerant maize genotypes.  The effects of soaking maize seeds in glyphosate solution under controlled conditions were studied on seed germination rate, seedling morphological indices, seedling growth and leaf chlorophyll content.  These responses were compared among a glyphosate-tolerant transgenic maize cultivar CC-2, glyphosate-susceptible inbred line Zheng 58 (the recurrent parent of CC-2) and hybrid cultivar Zhengdan 1002.  The results showed that the germination rate, seedling morphological indices and leaf chlorophyll content of glyphosate-tolerant CC-2 seeds did not change significantly among five different concentrations of glyphosate treatment (0 to 2%).  In contrast, germination rates, seedling morphological indices and leaf chlorophyll contents of Zheng 58 and Zhengdan 1002 seeds were significantly negatively affected by exposure to increasing concentrations of glyphosate.  The glyphosate-tolerant inbred line CC-2 displayed a strong tolerance to glyphosate after soaking in 0.1 to 2.0% glyphosate solutions, while both the inbred line Zheng 58 and hybrid Zhengdan 1002 were susceptible to glyphosate.  The accuracy of the glyphosate-soaking method for screening glyphosate-tolerant maize was confirmed using a field spraying trial.
    Molecular identification and enzymatic properties of laccase2 from the diamondback moth Plutella xylostella (Lepidoptera: Plutellidae)
    LIU Zhen-gang, WANG Huan-huan, XUE Chao-bin
    2018, 17(10): 2310-2319.  DOI: 10.1016/S2095-3119(17)61764-7
    Abstract ( )   PDF in ScienceDirect  
    Laccase (EC is known to oxidize various aromatic and nonaromatic compounds via a radical-catalyzed reaction, which generally includes two types of laccase, Lac1 and Lac2. Lac1 oxidizes toxic compounds in the diet, and Lac2 is known to play an important role in melanizing the insect exoskeleton. In this study, we cloned and sequenced the cDNA of the diamondback moth, Plutella xylostella Lac2 (PxLac2), from the third instar larvae using polymerase chain reaction (PCR) and rapid amplification of cDNA ends techniques. The results showed that the full-length PxLac2 cDNA was 1 944 bp long and had an open reading frame of 1 794 bp. PxLac2 encoded a protein with 597 amino acids and had a molecular weight of 66.09 kDa. Moreover, we determined the expression levels of PxLac2 in different stages by quantitative PCR (qPCR). The results indicated that PxLac2 was expressed differently in different stages. We observed the highest expression level in pupae and the lowest expression level in fourth instar larvae. We also investigated the enzymatic properties of laccase, which had optimal activity at pH 3.0 and at 35°C. Under these optimal conditions, laccase had a Michaelis constant (Km) of 0.97 mmol L−1, maximal reaction speed (Vm) of 56.82 U mL−1, and activation energy (Ea) of 17.36 kJ mol−1 to oxidize 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid ammonium salt). Type II copper enhanced laccase activity below 0.8 mmol L−1 and reduced enzyme activity above 0.8 mmol L−1 with an IC50 concentration of 1.26 mmol L−1. This study provides insights into the biological function of laccase.
    Animal Science · Veterinary Medicine
    Beneficial role of melatonin in protecting mammalian gametes and embryos from oxidative damage
    PANG Yun-wei, JIANG Xiao-long, ZHAO Shan-jiang, HUANG Zi-qiang, ZHU Hua-bin
    2018, 17(10): 2320-2335.  DOI: 10.1016/S2095-3119(18)61942-2
    Abstract ( )   PDF in ScienceDirect  

    Mammalian gametes and embryos are particularly vulnerable to oxidative stress-induced damage, which is mainly caused by reactive oxygen species (ROS) originating from normal metabolism and/or the external environment.  Several researchers have implicated the role of oxidative stress in the activation of apoptosis, causing peroxidative damage to sperms/oocytes and inducing embryo fragmentation, arrest, or demise.  Melatonin is a tryptophan derivative that is known for its powerful free radical-scavenging activity and broad-spectrum antioxidant property.  Numerous studies have shown that melatonin and its metabolic derivatives can sequentially detoxify ROS in an antioxidant cascade, and modulate various antioxidant enzymes via its receptors to prevent radical-mediated damage.  The identification of melatonin receptors in cumulus/granulosa cells, oocytes, and epididymal tissues implies that melatonin has protective actions on gametes and embryos.  Enriching the semen extender or culture medium with melatonin significantly benefits sperm characteristics, improves oocyte maturation potential and quality, and enhances the developmental competence of preimplantation embryos.  Certainly, further comparative studies are needed to show the unique antioxidant role and the advantage of melatonin in this field.  This review summarizes the harmful effects of ROS and the beneficial role of melatonin against oxidative damage of gametes and embryos. 

    Effects of lairage after transport on post mortem muscle glycolysis, protein phosphorylation and lamb meat quality
    LI Xin, XIA An-qi, CHEN Li-juan, DU Man-ting, CHEN Li, KANG Ning, ZHANG De-quan
    2018, 17(10): 2336-2344.  DOI: 10.1016/S2095-3119(18)61922-7
    Abstract ( )   PDF in ScienceDirect  
    The objective of this study was to investigate the effect of lairage after transport on post mortem muscle glycolysis, protein phosphorylation and lamb meat quality.  Two preslaughter animal treatments, transport for 3 h and lairage for 0 h (T3L0) and transport for 3 h and then lairage for 12 h (T3L12), were compared with a control treatment of 0 h transport and 0 h lairage.  Data obtained showed that preslaughter transport had a significant effect on lamb meat quality.  Loins from lambs of the T3L0 treatment showed higher (P=0.026) pH24 h and higher (P=0.021) pH48 h values, but lower (P<0.001) drip loss and lower (P<0.05) glycolytic potential at 0 h post mortem than those of the T3L12 and control groups.  Muscle samples of the T3L0 group showed higher (P=0.046) shear force and lower (P=0.005) b* value than those of the T3L12 group.  Muscle glycogen concentration at 0, 2, 4 h post mortem were lower (P<0.05) in the T3L0 group than in control.  No significant difference (P>0.05) in most meat quality parameters was determined between the T3L12 group and control, showing lairage for 12 h allowed lambs to recover from the effects of transport for 3 h and resulted in similar meat quality characteristics compared to no transport.  Lairage after transport did not affect most meat quality indices in comparison with control, but increased the meat drip loss and b* value of lambs possibly through decreasing glycogen concentration and glycolytic potential.
    Agricultural Economics and Management
    Determinants of cooperative pig farmers' safe production behaviour in China – Evidences from perspective of cooperatives' services
    JI Chen, CHEN Qin, Jacques Trienekens, WANG Hai-tao
    2018, 17(10): 2345-2355.  DOI: 10.1016/S2095-3119(18)62058-1
    Abstract ( )   PDF in ScienceDirect  
    Farmers’ production behaviour is a key to ensuring the safety and quality of their final products, and cooperatives play an important role in shaping that behaviour.  This paper aims to explore the determinants of pig farmers' safe production behaviour, giving special focus from the perspective of cooperatives’ services.  This study adopted cross sectional survey data from 27 pig cooperatives and their 540 farmers in China to test the influence of cooperatives’ services on farmers’ safe production behaviour.  The hypotheses were tested using a logit regression model.  The findings indicated that although the number of services is not a key determinant of farmers’ safe production behaviour, service quality matters.  When a cooperative is strongly capable of involving more farmers in certain services, and provides certain services in more frequency, member farmers behave more safely.  The results also show that veterinarian and pig-selling services play an important role in ensuring farmers’ safe production behaviour.  For this study, the quality of cooperatives’ services is implied to have a positive impact on farmers’ safe production behaviour.  Leaders/managers of cooperatives must try to improve the quality of their services instead of merely attempting to provide a large number of services.  For government officials and policy makers, designing policies that encourage cooperatives to improve their service quality is important.  This research contributes to the scant literature on how cooperative services could help farmers engage in safer production behaviour, which would improve the safety of pork products in the future.
    The trade margins of Chinese agricultural exports to ASEAN and their determinants
    SUN Zhi-lu, LI Xian-de
    2018, 17(10): 2356-2367.  DOI: 10.1016/S2095-3119(18)62084-2
    Abstract ( )   PDF in ScienceDirect  
    How do Chinese agricultural exports to ASEAN (Association of Southeast Asian Nations) evolve? And what factors affected the evolution pattern? This study measures the trade margins of Chinese agricultural exports to ASEAN by utilizing the 2000–2015 Harmonized System’s six-digit agricultural trade data, and further analyzes their determinants by developing an augmented gravity model of international trade. The results indicate that, the main growth source of Chinese agricultural exports to ASEAN has shifted from the extensive margin before the formal establishment of CAFTA (China–ASEAN Free Trade Area) in 2010 to the intensive margin since the formal establishment of CAFTA, but changes in Chinese agricultural exports to ASEAN have always mainly depended on the intensive margin. Since the formal establishment of CAFTA, the evolution pattern of Chinese agricultural exports to ASEAN has shifted from “more varieties, low price, and small quantity” to “less varieties, high price, and large quantity”. Relative economic scale, relative population scale, capacity of agricultural export, trade integration, global financial crisis, and common border significantly affect the trade margins of Chinese agricultural exports to ASEAN.