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    Weed growth, herbicide efficacy, and rice productivity in dry seeded paddy field under different wheat stubble management methods
    Muhammad Zia-Ul-Haq, Abdul Khaliq, Qiang Sheng, Amar Matloob, Saddam Hussain, Saba Fatima, Zeshan Aslam
    2019, 18 (4): 907-926.   DOI: 10.1016/S2095-3119(18)62004-0
    Abstract250)      PDF (1875KB)(239)      
    To ascertain the influence of wheat stubble management options and chemical weed control methods on weed growth and productivity of dry direct-seeded fine rice, a two years’ field study was undertaken at the Agronomic Research Farm, University of Agriculture, Faisalabad, Pakistan in 2013 and 2014.  Different wheat stubble management methods, viz., incorporation, burning and retention were executed during seed-bed preparation.  While, herbicide treatments comprised of a weed check, weed free, pendimethalin followed by tank mixture of fenoxaprop p-ethyl+ethoxysulfuron ethyl, and bispyribac sodium followed by tank mixture of fenoxaprop p-ethyl+ethoxysulfuron ethyl.  Results revealed that weed control efficacy of both herbicide treatments ranged from 84 to 94%.  Herbicide treatments significantly reduced weed density (88–90%) and dry weight (86–88%), while improved the rice growth attributes compared with weed check.  Application of bispyribac sodium followed by tank mixture of fenoxaprop p-ethyl+ethoxysulfuron ethyl in stubble retention recorded 226 and 273% increase in kernel yield over weedy check in 2013 and 2014, respectively.  In stubble incorporation, pendimethalin followed by tank mixture of fenoxaprop p-ethyl+ethoxysulfuron ethyl was more effective in increasing (256–293%) rice yields over weedy check.  Among different treatment combinations, the maximum net benefits (1 397.49–1 472.22 USD ha–1), net returns (636–700 USD ha–1), benefit cost ratio (1.77–1.83) and marginal rate of return (2 187–2 330%) were recorded with the application of bispyribac sodium followed by fenoxaprop p-ethyl+ethoxysulfuron ethyl in stubble retention.  In crux, application of bispyribac sodium followed by tank mixture of fenoxaprop p-ethyl+ethoxysulfuron ethyl in stubble retention is efficient approach to control weeds, and get maximum rice productivity and net economic returns under dry seeded system.
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    An investigation of weed seed banks reveals similar potential weed community diversity among three different farmland types in Anhui Province, China
    HE Yun-he, GAO Ping-lei, QIANG Sheng
    2019, 18 (4): 927-937.   DOI: 10.1016/S2095-3119(18)62073-8
    Abstract267)      PDF (1086KB)(508)      
    Crop type is one of main factors influencing weed community structure.  However, the identity of weed communities associated with the cultivation of different crops in farmlands remains largely unclear.  A field survey of weed seed banks was conducted in 2 280 fields at 228 sites of 62 locations representing three different types of farmland (95 paddy, 73 summer-ripe, and 60 autumn-ripe farmlands) along the bank of the Yangtze River in Anhui Province, China.  A total of 43 families and 174 species of weeds were found in these weed seed banks.  A comparison of the composition of weed groups in the seed banks showed that the species number and density percentage of grass, sedge and broadleaf weed groups were similar among the different types of farmland.  The seed banks of all three farmland types shared 71 common weed species, accounting for 40.80% of the total number of species.  These common weeds, which were both associated and not associated with crops, accounted for 91.71% of the total dominance degree among all farmland types.  The crop-associated weed species were distributed in all soil layers of each farmland type.  The Shannon-Wiener index (description of species diversity which is more sensitive to dense species) and Pielou’s evenness index J (description of species evenness) in summer-ripe farmland were similar to those in autumn-ripe farmland but differed from those in paddy farmland.  However, the Simpson’s index D (description of species diversity which is more sensitive to sparse species) was similar among all three farmland types.  The results of similarity comparison indicated that although the aboveground weed community differed among the different cropping patterns, the weed species composition in the soil seed bank was still similar.  Consequently, our results demonstrate that after the implementation of long-term monoculture patterns, weed species compositions in the soil seed bank in different farmlands become homogenized regardless of the crop type. 
     
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    Preparation and characterization of atrazine-loaded biodegradable PLGA nanospheres
    CHEN Xiao-ting, Tongxin Wang
    2019, 18 (5): 1035-1041.   DOI: 10.1016/S2095-3119(19)62613-4
    Abstract158)      PDF in ScienceDirect      
    Atrazine is the second mostly used herbicide in USA, but low utilization ratio causes severe environmental problem, so controlled release system is highly needed in order to minimize the negative impact on environment.  In this paper, a herbicide delivery system, atrazine-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) were prepared by forming an oil-in-water emulsion using the emulsion-solvent evaporation method.  By varying the preparation conditions of PLGA-NPs, such as sonication time, surfactant content, solvent fraction, and polymer content, the particle sizes of the PLGA-NPs were well controlled from 204 to 520 nm.  The morphology and size distribution of PLGA-NPs were evaluated using dynamic light scattering (DLS) and scanning electron microscopy (SEM).  Both the encapsulation efficiency and release profile of the herbicide from the PLGA-NPs were typically evaluated by using 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine (atrazine, ATZ) as the model.  ATZ encapsulation efficiency within the PLGA-NPs was ranged from 31.6 to 50.5%.  The release profiles of ATZ-loaded PLGA-NPs exhibited a much slower release rate in comparison with that of pure herbicide.  The results demonstrated that the prepared PLGA-NPs had a high encapsulation efficiency and slow release rate, which could be used as a promising herbicide release system in agriculture to diminish the impact on the environment and minimize the potential harm to the farmers. 
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    Effect of tillage and burial depth and density of seed on viability and seedling emergence of weedy rice
    ZHANG Zheng, GAO Ping-lei, DAI Wei-min, SONG Xiao-ling, HU Feng, QIANG Sheng
    2019, 18 (8): 1914-1923.   DOI: 10.1016/S2095-3119(19)62583-9
    Abstract148)      PDF in ScienceDirect      
    Weedy rice (Oryza sativa f. spontanea) is one of the three worst paddy weeds in most rice growing areas.  The unexpected heavy infestation is derived from a persistence of soil seed bank of weedy rice, which the shattered seeds chiefly feed back to.  Information on soil seed bank dynamics is imperative to predict the infestation of weeds.  In the present paper, the effect of rotary tillage on weedy rice seed bank structure was studied first, and a burial experiment of marked seeds was conducted to observe the overwintering survival, seed viability and seedling emergence of weedy rice.  The results showed that the proportion of weedy rice seeds in deeper soil increased but seedling emergence decreased with increasing plowing depth.  The viability of weedy rice seeds decreased as the burial duration time extended but more slowly in deeper soil layers.  Additionally, there was no significant effect of burial density on seed viability.  Moreover, the logistic model fitted well (R2≥0.95, P≤0.01) with the depressive trends of seed viability with increasing burial time under all burial depths and densities which can provide us further information about seed survival.  In field experiments, number of seedling emergence significantly decreased as seed burial depth increased, conversely, proportion of seedling emergence increased as seed burial density decreased.  This study has important implications for determining strategies for weedy rice management by exhausting its seed bank through the alteration of tillage practices.
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    Fitness of F1 hybrids between stacked transgenic rice T1c-19 with cry1C*/bar genes and weedy rice
    HUANG Yao, WANG Yuan-yuan, QIANG Sheng, SONG Xiao-ling, DAI Wei-min
    2019, 18 (12): 2793-2805.   DOI: 10.1016/S2095-3119(19)62662-6
    Abstract85)      PDF in ScienceDirect      
    Compared to single-trait transgenic crops, stacked transgenic plants may be more prone to become weedy, and transgene flow from stacked transgenic plants to weedy relatives may pose a potential environmental risk because these hybrids could be more advantageous under specific environmental conditions.  Evaluation of the potential environmental risk caused by stacked transgenes is essential for assessing the environmental consequences caused by crop-weed transgene flow.  The agronomic performance of fitness-related traits was assessed in F1+ (transgene positive) hybrids (using the transgenic line T1c-19 as the paternal parent) in monoculture and mixed planting under presence or absence glufosinate pressure in the presence or absence of natural insect pressure and then compared with the performance of F1– (transgene negative) hybrids (using the non-transgenic line Minghui 63 (MH63) as the paternal parent) and their weedy rice counterparts.  The results demonstrated that compared with the F1– hybrids and weedy rice counterparts, the F1+ hybrid presented higher performance (P<0.05) or non-significant changes (P>0.05) under natural insect pressure, respectively, lower performance (P<0.05) or non-significant changes (P>0.05) in the absence of insect pressure in monoculture planting, respectively.  And compared to weedy rice counterparts, the F1+ hybrid presented higher performance (P<0.05) or non-significant changes (P>0.05) in the presence or absence of insect pressure in mixed planting, respectively.  The F1+ hybrids presented non-significant changes (P>0.05) under the presence or absence glufosinate pressure under insect or non-insect pressure in monoculture planting.  The all F1+ hybrids and two of three F1– hybrids had significantly lower (P<0.05) seed shattering than the weedy rice counterparts.  The potential risk of gene flow from T1c-19 to weedy rice should be prevented due to the greater fitness advantage of F1 hybrids in the majority of cases. 
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    Herbicidal activity of Aureobasidium pullulans PA-2 on weeds and optimization of its solid-state fermentation conditions
    GUO Qing-yun, CHENG Liang, ZHU Hai-xia, LI Wei, WEI You-hai, CHEN Hong-yu, GUO Liang-zhi, WENG Hua, WANG Jian
    2020, 19 (1): 173-182.   DOI: 10.1016/S2095-3119(19)62738-3
    Abstract100)      PDF in ScienceDirect      
    Fungal strain PA-2 was isolated from infected poplar leaves from the Ping’an District, Haidong City of Qinghai Province, China.  Based on the culture characteristics and the internal transcribed spacer (ITS) sequence of its 16S rDNA, the strain was identified as Aureobasidium pullulans.  The culture and metabolites of strain PA-2 showed high herbicidal potential to five tested weeds Galium aparine var. tenerum, Chenopodium album, Malva crispa, Polygonum lapathifolium and Avena fatua.  For the in vitro test, 5 days after the detached leaves were inoculated with PA-2 culture, all leaves infected by the hyphae and became black and rotten.  For the in vivo test, a metabolite filtrate of PA-2 culture was sprayed over the living weed plants, and five days after inoculation, the weed plants became withered and necrotic.  Seven days after inoculation, the fresh weight reductions of G. aparine var. tenerum, C. album, M. crispa, P.?lapathifolium and A.?fatua were 87.25, 78.46, 82.25, 62.11, and 80.27%, respectively.  Galium aparine var. tenerum and M. crispa exhibited significant reductions in fresh weight.  The bio-safety test on the five crops showed no significant plant height reductions, which was also observed for wheat (Triticum aestivum), faba bean (Vicia faba), and barley (Hordeum vulgare).  By contrast, oilseed rape (Brassica napus) and pea (Pisum sativum) exhibited light spots but no significant reductions in plant height.  These results indicated that A.?pullulans could be a potential microbial herbicide for the control of the target weeds in crops.  Optimization of the carbon and nitrogen sources for cultural media and substances for solid-state fermentation indicated that PA-2 had better colony growth and spore production with the optimal carbon source of glucose (C4), nitrogen source of soybean flour (N2), and the optimal substance was wheat bran.  The results in this study provide useful information for the development of A.?pulluans PA-2 as an herbicide for bio-control of the weed.
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    Beneficial rhizobacterium provides positive plant–soil feedback effects to Ageratina adenophora
    SUN Yuan-yuan, ZHANG Qiu-xin, ZHAO Yun-peng, DIAO Yue-hui, GUI Fu-rong, YANG Guo-qing
    2021, 20 (5): 1327-1335.   DOI: 10.1016/S2095-3119(20)63234-8
    Abstract94)      PDF in ScienceDirect      
    Rhizosphere microbial communities play important roles in facilitating or inhibiting the establishment of exotic species.  Since some invasive plants interact with soil microbial communities such as rhizosphere bacteria, changes triggered by rhizosphere bacteria may alter competitive interactions between exotic and native plants.  This study compared the Bacillus cereus content in soils with different degrees of Ageratina adenophora invasion, and investigated the effects of A. adenophora allelochemicals on B. cereus growth and soil characteristics and the feedback effects of B. cereus on A. adenophora growth.  Bacillus cereus content in the rhizosphere of A. adenophora increased with intensification of the invasion process, and newly invaded soil contained almost twice as much bacteria as noninvaded soil.  When rhizosphere soil was added to the root exudates of A. adenophora, the contents of B. cereus were twice as much as the control, except on the first day.  Certain soil parameters increased significantly, such as ammonium nitrogen (NH4+-N) and available phosphorus (AP), which were increased by 41 and 27%, respectively.  Soil treatment with B. cereus promoted the degradation of two allelochemicals from the rhizosphere of A. adenophora, amorpha-4,7(11)-dien-8-one and 6-hydroxy-5-isopropy1-3,8-dimethyl-4a,5,6,7,8,8a-hexahydraphthalen-2(1H)-one, to varying degrees; and increased the germination rate by 50%, root length by 117%, shoot length by 48% and fresh weight by 81% for A. adenophora compared to those of untreated soil.  Our results confirmed that the invasion of A. adenophora will promote an increase of B. cereus, a beneficial rhizosphere bacterium, which in turn induces a positive feedback effect on A. adenophora.
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    Transcriptomic analysis reveals the transcription factors involved in regulating the expression of EPSPS gene, which confers glyphosate resistance of goosegrass (Eleusine indica)
    ZHANG Chun, YU Chao-jie, ZHANG Tai-jie, GUO Wen-lei, TIAN Xing-shan
    2021, 20 (8): 2180-2194.   DOI: 10.1016/S2095-3119(21)63682-1
    Abstract136)      PDF in ScienceDirect      
    Glyphosate inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) and overexpression of the EPSPS gene is one of the molecular mechanisms conferring glyphosate resistance in weeds.  A regulatory sequence of EPSPS gene was isolated previously, and an alteration in its 5´-untranslated region (UTR) pyrimidine (Py)-rich stretch element is involved in the regulation of EPSPS expression in glyphosate-resistant (GR) Eleusine indica.  However, the transcription factors involved in this regulatory sequence remain to be elucidated.  In this study, we investigated the regulatory network of EPSPS overexpression associated genes in a GR E. indica population by RNA-seq.  The differentially expressed transcript analyses revealed that glyphosate treatment caused an increase in the expression of 2 752 unigenes and a decrease in the expression of 4 025 unigenes in the GR E. indica, compared to the glyphosate-susceptible (GS) E. indica.  Among them, 1 373 unigenes were identified to be co-expressed with the EPSPS gene in GR E. indica.  GO and KEGG pathway analyses showed that the up-regulated unigenes were mainly enriched in chloroplasts and associated with the shikimate biosynthesis pathway, chlorophy II and peroxisome metabolism processes.  Notably, the expression of a Shikimate kinase which catalyzed the conversion of Shikimate to Shikimate 3-phosphate (S3P, a substrate of EPSPS), was also up-regulated.  Eight transcription factors were identified as likely to be involved in the regulation of the EPSPS expression, and three of them (ARF2, ARF8 and BPC6) showed more binding sites because of a (CT)n insertion of the 5´-UTR Py-rich stretch element in GR.  However, the yeast one-hybrid assay illustrated that ARF8 and BPC6 could bind to the 5´-UTR Py-rich stretch element of wild type EPSPS, but could not bind to the mutated form.  Our data suggests that the transcriptional regulation of EPSPS expression is complex and was significantly altered in GR E. indica.  These discoveries provide new references for further study of the EPSPS overexpression mechanism that endows glyphosate resistance. 
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