2021 Vol. 20 No. 5 Previous Issue    Next Issue

    Special Focus: Resource utilization of agricultural solid waste
    Crop Science
    Plant Protection
    Animal Science · Veterinary Medicine
    Agricultural Economics and Management

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    Special Focus: Resource utilization of agricultural solid waste
    Editorial - Resource utilization of agricultural solid waste
    2021, 20(5): 1119-1120.  DOI: 10.1016/S2095-3119(21)63648-1
    Abstract ( )   PDF in ScienceDirect  
    China, one of the world’s largest agricultural countries, inevitably generates a massive amount of agricultural solid waste (ASW) every year.  As it is estimated, China annually produced 3.8 billion, 900 million and 200 million tons of livestock and poultry manure, crop straw, and agricultural product processing waste, respectively (Cong et al. 2020).  As an important renewable resource, ASW has great potential and value for resource utilization.  Efficient utilization of ASW is not only beneficial to environmental protection, but also provides great economic benefits.  Since the beginning of the 21st century, research has been fruitful on how to utilize livestock and poultry manure by microbial conversion (Chen et al. 2019; Feng et al. 2020).  However, we have not yet fully understood the changes in microbial diversity and its interaction with different heavy metals during the microbial conversion process of crop straw and agricultural product processing waste.  In addition, insect-based bioconversion (i.e., by earthworms, black soldier flies, etc.) is an emerging and high-value method for ASW treatment.  However, more research is needed to identify the factors influencing the insect-based bioconversion process, investigate the role of microorganisms, and explore the conversion mechanisms in which ASW is converted into multiple valuable commodities by insects, such as proteins, biofuels, fertilizers, etc.  Therefore, in this special focus of ‘Resource utilization of agricultural solid waste’, five papers, respectively contributed by Chang et al. (2021), Cui et al. (2021), Liu et al. (2021), Wang et al. (2021) and Zhang et al. (2021), showcase the latest research progress on ASW utilization.  Chang et al. (2021) report the dynamics of microbial diversity during crop straw composting.  Cui et al. (2021) demonstrate that the addition of phosphate rock in swine manure and maize straw composting could reduce the bioavailability of heavy metals by influencing the bacterial communities.  Liu et al. (2021) evaluate the feasibility to employ stevia residue in eco-friendly fermentation of Trichoderma guizhouense.  Wang et al. (2021) investigate the changes in speciation, mobility and bioavailability of different heavy metals during the conversion process of pig manure by black soldier flies.  Zhang et al. (2021) summarize the functional characteristics of microorganisms, influencing factors (such as larval density, manure temperature, type of manure and so on), and possible mechanisms during the conversion processes of livestock and poultry manure by black soldier fly larvae.  It is hoped that the studies presented in this special focus could enhance our basic and applied knowledge in the field of resource utilization of ASW, and stimulate further innovative research in this area.
    Dynamics of microbial diversity during the composting of agricultural straw
    CHANG Hui-qing, ZHU Xiao-hui, WU Jie, GUO Da-yong, ZHANG Lian-he, FENG Yao
    2021, 20(5): 1121-1136.  DOI: 10.1016/S2095-3119(20)63341-X
    Abstract ( )   PDF in ScienceDirect  
    The dynamic changes in microbial diversity during the aerobic composting of agricultural crop straw with additives were evaluated using high-throughput sequencing at four phases of composting (mesophilic, thermophilic, cooling and maturation phases).  In addition, the physicochemical parameters of the composting system were determined in this study.  The fermentation time of the thermophilic period was prolonged with the addition of urea or urea combined with a microbial agent.  The ratio of C/N and germination index variation indicated that the additives were favorable for composting, because the additives directly changed the physicochemical properties of the compost and had effects on the diversity and abundance of bacteria and fungi.  The abundance of operational taxonomic units (OTUs), diversity index (Shannon) and richness index (Chao1) of fungi and bacteria were found to significantly increase when urea+microbial agents  were added to straw in the thermophilic phase.  The relative abundance of the predominant bacteria and fungi at the phylum and genus levels differed during different composting phases.  The abundance of the phyla Firmicutes and Proteobacteria declined in the order of treatments SNW>SN>S (S is straw only compost; SN is straw+5 kg t–1 urea compost; and SNW is straw+5 kg t–1 urea+1 kg t–1 microbial agent compost) in the thermophilic phase.  The abundance of the genera Staphylococcus, Bacillus and Thermobifida followed the same order in the mesophilic phase.  Ascomycota accounted for more than 92% of the total fungal sequences.  With the progression of the composting process, the abundance of Ascomycota decreased gradually.  The abundance of Ascomycota followed the order of S>SN>SNW during the thermophilic phase.  The abundance of Aspergillus accounted for 4–59% of the total abundance of fungi and increased during the first two sampling periods.  Aspergillus abundance followed the order of SNW>SN>S.  Additionally, principal component analysis (PCA) revealed that the community compositions in the straw and straw+urea treatments were similar, and that the bacterial communities in treatments S, SN and SNW in the mesophilic phase (at day 1) were different from those observed in three other phases (at days 5, 11, and 19, respectively), while the fungal communities showed only slight variations in their structure in response to changes in the composting process.  Canonical correlation analysis (CCA) and redundancy analysis (RDA) showed that total carbon (TC), NO3-N (NN), electrical conductivity (EC) and pH were highly correlated with community composition.  Therefore, this study highlights that the additives are beneficial to straw composting and result in good quality compost.
    Phosphate rock reduces the bioavailability of heavy metals by influencing the bacterial communities during aerobic composting
    CUI Hu, OU Yang, WANG Li-xia, YAN Bai-xing, LI Ying-xin, DING Da-wei
    2021, 20(5): 1137-1146.  DOI: 10.1016/S2095-3119(20)63300-7
    Abstract ( )   PDF in ScienceDirect  
    Available information on the microbial mechanisms associated with heavy metal (HM) passivation during co-composting amended with phosphate rock (PR) remains limited.  Thus, this study investigated the dynamic changes in bacterial communities and HM-fractions (Zn, Cu, Cd, Cr and Pb) during swine manure composting with maize straw, and ascertained the bacterial influence on HM-passivation.  The results demonstrated that the addition of PR improved HM-passivation, especially for Zn and Cd, with their bioavailability factors (BFs) reduced by 247.41 and 176.25%, respectively.  As for bacterial communities, the proportion of Firmicutes decreased, while the proportions of Proteobacteria, Bacteroidetes, Deinococcus-Thermus and Gemmatimonadetes increased in all treatments.  PR significantly changed the primary bacterial phyla in the thermophilic phase.  Bacteroidetes were the main bacterial component controlling the passivation of Zn, Cu and Cr, while Deinococcus-Thermus mainly regulated the mobility of Zn and Pb, and Proteobacteria only dominated the transformation among Cd-fractions.  These results may provide a reference for the use of HM-passivation techniques during composting.
    Spore production in the solid-state fermentation of stevia residue by Trichoderma guizhouense and its effects on corn growth
    LIU Hong-jun, DUAN Wan-dong, LIU Chao, MENG Ling-xue, LI Hong-xu, LI Rong, SHEN Qi-rong
    2021, 20(5): 1147-1156.  DOI: 10.1016/S2095-3119(20)63478-5
    Abstract ( )   PDF in ScienceDirect  
    Trichoderma is an important and widely used plant growth-promoting fungus (PGPF).  In this study, stevia residue amended with amino acids hydrolyzed from animal carcasses was used for the production of Trichoderma guizhouense NJAU 4742 by solid-state fermentation, and then its potential to promote corn plant growth was evaluated in combination with chemical fertilizer (CF) or organic fertilizer (OF).  The highest spore number of 7×109 CFU g–1 fresh weight was obtained under the following optimal parameters: material ratio of 50% (stevia residue:rice bran=1:1), pH value of 3.0 (amended with 6.67% amino acids), initial moisture content of 60%, inoculum size of 10%, material thickness of 3 cm and an incubation time of 4 days.  The aboveground corn plant biomass obtained with T. guizhouense applied alone and with CF treatments were slightly higher than those of no fertilizer control and CF treatments, respectively.  However, T. guizhouense applied with OF significantly (P<0.05) increased aboveground biomass compared to OF and yielded the highest aboveground biomass among all the treatments.  Moreover, T. guizhouense applications primarily in?uenced the fungal bulk soil community composition, among which three OTUs (OTU_2 and OTU_9 classified as Chaetomium, and OTU_4 classified as Trichoderma) were stimulated in both bulk and rhizosphere soil.  Notably, a specific OTU_3 (Phymatotrichopsis) was only stimulated by T. guizhouense applied with OF, possibly leading to high soil productivity.  These results show that it is feasible to employ stevia residue in the eco-friendly fermentation of T. guizhouense, which is strongly suggested for enhancing OF applications.
    Changes in speciation, mobility and bioavailability of Cd, Cr and As during the transformation process of pig manure by black soldier fly larvae (Hermetia illucens)
    WANG Xiao-bo, WU Nan, CAI Rui-jie, GENG Wei-na, XU Xiao-yan
    2021, 20(5): 1157-1166.  DOI: 10.1016/S2095-3119(20)63333-0
    Abstract ( )   PDF in ScienceDirect  
    The black soldier fly larvae (BSFL) (Hermetia illucens) are a good candidate for poultry and livestock manure treatment.  The harvested insect bodies and feces can be used as animal feed and organic fertilizer.  However, heavy metals have a negative impact on the transformation process of the manure by BSFL.  Here we evaluated the effects of Cd, Cr and As in pig manure on the growth of BSFL, as well as the mobility and changes in speciation of the metals during the transformation process.  The results showed that As significantly reduced the weight of BSFL, but Cr and Cd had no significant effects on BSFL growth.  The bioaccumulation factors (BAFs) at various concentrations of Cd (2.8–3.7) were significantly higher than those of Cr (0.44–0.62) and As (0.43–0.45).  The heavy metals in pig manure were mainly transferred to BSFL feces, and the distribution percentages of Cd, Cr and As in the BSFL feces were 52.6–62.0%, 90.3–94.2% and 93.0–93.3%, respectively.  Cd concentrations in BSFL feces were significantly lower than those in the pig manure, while there were no significant differences in the concentrations of Cr and As between BSFL feces and pig manure (except for the treatment with the addition of 150 mg Cr kg–1).  The metal speciation (weak acid soluble, reducible, oxidizable and residual fractions) in BSFL feces obviously changed when compared with pig manure.  In BSFL feces, the reducible proportion of Cr decreased while the oxidizable proportion increased.  Cd mainly existed in the weak acid soluble and reducible states in pig manure and BSFL feces.  For As, the proportions of weak acid soluble and reducible states decreased in BSFL feces.  After the BSFL transformation process, the bioavailable fraction of Cr decreased by 17.3–23.1%, but those of Cd and As did not change significantly, except for As in the CK group.  These findings contribute to our understanding of the roles of BSFL during the biotransformation process of livestock manure as well as the safe utilization of transformed products.
    Black soldier fly: A new vista for livestock and poultry manure management
    ZHANG Ji-bin, ZHANG Jia, LI Jia-hui, Jeffery K. TOMERLIN, XIAO Xiao-peng, Kashif ur REHMAN, CAI Min-min, ZHENG Long-yu, YU Zi-niu
    2021, 20(5): 1167-1178.  DOI: 10.1016/S2095-3119(20)63423-2
    Abstract ( )   PDF in ScienceDirect  
    The number of intensive livestock and poultry farms is expected to increase substantially in future because of consumer demand.  Unfortunately, such demand also results in a great deal of manure being generated, which threatens the environment if it is not properly managed.  Concurrent developments in biotransformation of these wastes with the black soldier fly (BSF), Hermetia illucens (L.) (Diptera: Stratiomydiae), demonstrates such concerns can be abated, while also producing products (e.g., protein, chitin, biodiesel, and fertilizer) of value.  In this review, we analyzed the factors influencing black soldier fly larvae (BSFL) conversion processes, the role of microorganisms, and the mechanisms used by BSFL when converting livestock and poultry manure into these valuable products.  The effects of BSFL conversion technology on reducing the hazards of such materials and their associated pathogens are reviewed, and the economics of livestock and poultry manure conversion by BSF larvae is discussed. 
    Crop Science
    QTL mapping of seedling biomass and root traits under different nitrogen conditions in bread wheat (Triticum aestivum L.)
    YANG Meng-jiao, WANG Cai-rong, Muhammad Adeel HASSAN, WU Yu-ying, XIA Xian-chun, SHI Shu-bing, XIAO Yong-gui, HE Zhong-hu
    2021, 20(5): 1180-1192.  DOI: 10.1016/S2095-3119(20)63192-6
    Abstract ( )   PDF in ScienceDirect  
    Plant nitrogen assimilation and use efficiency in the seedling’s root system are beneficial for adult plants in field condition for yield enhancement.  Identification of the genetic basis between root traits and N uptake plays a crucial role in wheat breeding.  In the present study, 198 doubled haploid lines from the cross of Yangmai 16/Zhongmai 895 were used to identify quantitative trait loci (QTLs) underpinning four seedling biomass traits and five root system architecture (RSA) related traits.  The plants were grown under hydroponic conditions with control, low and high N treatments (Ca(NO3)2·4H2O at 0, 0.05 and 2.0 mmol L−1, respectively).  Significant variations among the treatments and genotypes, and positive correlations between seedling biomass and RSA traits (r=0.20 to 0.98) were observed.  Inclusive composite interval mapping based on a high-density map from the Wheat 660K single nucleotide polymorphisms (SNP) array identified 51 QTLs from the three N treatments.  Twelve new QTLs detected on chromosomes 1AL (1) in the control, 1DS (2) in high N treatment, 4BL (5) in low and high N treatments, and 7DS (3) and 7DL (1) in low N treatments, are first reported in influencing the root and biomass related traits for N uptake.  The most stable QTLs (RRS.caas-4DS) on chromosome 4DS, which were related to ratio of root to shoot dry weight trait, was in close proximity of the Rht-D1 gene, and it showed high phenotypic effects, explaining 13.1% of the phenotypic variance.  Twenty-eight QTLs were clustered in 12 genetic regions.  SNP markers tightly linked to two important QTLs clusters C10 and C11 on chromosomes 6BL and 7BL were converted to kompetitive allele-specific PCR (KASP) assays that underpin important traits in root development, including root dry weight, root surface area and shoot dry weight.  These QTLs, clusters and KASP assays can greatly improve the efficiency of selection for root traits in wheat breeding programmes.
    Establishment and application of an accurate identification method for fragrant soybeans
    ZHANG Yong-fang, ZHANG Chun-yan, ZHANG Bo, YIN Man, HONG Hui-long, YU Li-li, GAO Hua-wei, GU Yong-zhe, LIU Zhang-xiong, LI Fu-heng, QIU Li-juan
    2021, 20(5): 1193-1203.  DOI: 10.1016/S2095-3119(20)63328-7
    Abstract ( )   PDF in ScienceDirect  
    In order to screen the aroma characteristics of soybean, a new method was established which can quickly quantify the content of 2-acetyl-1pyrroline (2-AP), an important compound related to soybean aroma, using gas chromatography-mass spectrometry (GC-MS).  Based on peak profile, total peak area and retention time as test indexes, an accurate identification method for fragrant soybeans was established.  The optimum parameters of the protocol consisted of column temperature 70°C, sample injector temperature 180°C, optimum extraction alcohol content 1 mL, NaCl content 0.1 g, ultrasonication time 10 min, and extraction time 1 h, which were established by using the orthogonal test of single factors and three factors with four levels (L9(3)4).  2-AP content of leaves had significant correlations with seeds, which were easier to measure.  The protocol was simple and easy to carry out, consumed only small amounts of reagents, and provided accurate and reliable results with good reproducibility.  A total of 101 soybean genotypes from different geographical sources were analyzed using this protocol.  The results showed that the average content of 2-AP was 0.29 mg L–1, ranging from 0.094 to 1.816 mg L–1, and the genetic diversity index was 0.54.  Among all genotypes-tested, they were classified into three grades, including seven elite genotypes identified as “grade one fragrant soybeans”, which were Zhonglong 608, Heinong 88, Ha13-2958, Hongmiandou, Heinong 82, Huangmaodou, and Jiyu 21.  These results provide both an identification technique and several elite aroma genotypes for gene discovery and good quality breeding in soybean.
    Effects of different mechanical direct seeding methods on grain yield and lodging resistance of early indica rice in South China
    WANG Wen-xia, DU Jie, ZHOU Yan-zhi, ZENG Yong-jun, TAN Xue-ming, PAN Xiao-hua, SHI Qing-hua, WU Zi-ming, ZENG Yan-hua
    2021, 20(5): 1204-1215.  DOI: 10.1016/S2095-3119(20)63191-4
    Abstract ( )   PDF in ScienceDirect  
    Direct seeding of rice has become a main planting method due to the low labor input and high economic benefit in South China.  Dry direct seeding (DDS) has been widely used for single-season rice planting establishment.  However, few studies have examined the performance of early-season indica rice under mechanical dry direct seeding.  A two-year field experiment was conducted with two indica rice cultivars (i.e., Zhongjiazao 17 and Zhuliangyou 819) to study lodging characteristics and grain yield formation under DDS, flooded direct seeding (FDS) and wet direct seeding (WDS) patterns.  The results showed that the annual grain yield in DDS was higher by 14.42–26.34% for cultivar ZLY819 and 6.64–24.58% for cultivar ZJZ17 than in WDS and FDS, respectively, and these increases were mainly attributed to the improvement of the panicles.  The DDS pattern significantly increased the seedling emergence rate of early indica rice cultivars, and increased total dry weight and crop growth rate.  Meanwhile, shorter basal internodes, better stem diameter and stem wall thickness and lower lodging index were found in DDS in contrast to FDS and WDS.  In particular, DDS improved the stem lodging resistance.  Our results suggested that the appropriate direct seeding method was beneficial for improving the grain yield and lodging resistance of early indica rice.
    Changes of oxidative metabolism in the roots of wheat (Triticum aestivum L.) seedlings in response to elevated ammonium concentrations
    LIU Yang, LI Yu-xiang, LI Yi-xiang, TIAN Zhong-wei, HU Jin-ling, Steve ADKINS, DAI Ting-bo
    2021, 20(5): 1216-1228.  DOI: 10.1016/S2095-3119(20)63216-6
    Abstract ( )   PDF in ScienceDirect  
    To elucidate the response of oxidative metabolism, triggered by elevated ammonium (NH4+) concentrations, on root growth of wheat seedlings, Yumai 49 (NH4+-tolerant) and Lumai 15 (NH4+-sensitive) cultivars were supplied with either 5.0 mmol L–1 NH4+-N (EAC) or 5.0 mmol L–1 NO3-N (CON) under hydroponic conditions.  Root growth in both cultivars was significantly reduced under EAC, and the negative effect was greater in Lumai 15.  EAC enhanced the activities of monodehydroascorbate reductase and dehydroascorbate reductase in the roots of both cultivars, while it decreased ascorbic acid (ASA) content and GDP-mannose pyrophosphorylase (GMPase) activity at the 12th day after treatment in Lumai 15 by 62.0 and 71.4%; and in Yumai 49 by 38.8 and 62.2%, respectively, indicating that the regeneration of ASA was increased, but the biosynthesis of ASA was reduced under EAC treatment.  Moreover, EAC increased DHA/ASA, reactive oxygen species (ROS), and malondialdehyde contents, as well as antioxidant enzyme activities in the roots of both cultivars.  Relatively greater increases in ROS and soluble sugar, and lower antioxidant enzyme activities in Lumai 15 indicate severe disruption of oxidative metabolism when compared to Yumai 49.  Results reveal that the reduction of ASA biosynthesis via decreased GMPase activity under the EAC condition probably acts as a trigger for accumulated ROS and imbalanced redox status, resulting in root growth inhibition during wheat seedling growth stage.  Yumai 49, being an NH4+-tolerant cultivar, had the stronger capacity to protect itself from oxidative stress, which allowed it to retain a lower DHA to ASA ratio by maintaining a better redox homeostasis than could be maintained in the NH4+-sensitive cultivar Lumai 15.
    Nitrogen spraying affects seed Bt toxin concentration and yield in Bt cotton
    ZHANG Xiang, ZHOU Ming-yuan, LI Ya-bing, LIU Zhen-yu, CHEN Yuan, CHEN De-hua
    2021, 20(5): 1229-1238.  DOI: 10.1016/S2095-3119(20)63243-9
    Abstract ( )   PDF in ScienceDirect  
    Cotton bolls exhibit the lowest insecticidal efficacy among all organs of Bt cotton, which would ultimately affect the yield formation.  The objective of this study was to investigate the effects of different urea concentrations on the seed Bt protein contents, seed cotton yield and the corresponding protein metabolism mechanism.  The experiments were conducted during 2017–2018 cotton growing seasons.  Two cultivars, Sikang 3 (hybrid, SK3) and Sikang 1 (conventional, SK1), were treated with six urea concentrations and their seed Bt protein contents were compared during boll formation period.  The urea spray concentration had a significant effect on the seed Bt toxin content and seed cotton yield.  Spraying of either 5 or 6% urea led to higher insecticidal protein contents and higher seed cotton yield for both cultivars.  Moreover, the highest amino acid and soluble protein contents, as well as GPT and GOT activities, and lower protease and peptidase activities were observed at the 5 to 6% urea levels.  Significant positive correlations between the seed Bt toxin and amino acid contents, and between the seed Bt toxin content and GPT activities were detected.  The lower boll worm number and hazard boll rate were also observed with the 5 to 6% urea treatments, which may be the reason why nitrogen spraying increased the seed cotton yield.  Therefore, our results suggested that the seed Bt toxin content and insect resistance were impacted markedly by external nitrogen application, and 5 to 6% urea had the greatest effect on insect resistance.
    Ultrastructural studies of seed coat and cotyledon during rapeseed maturation
    CAO Jian-bo, HE Li-min, Chinedu Charles NWAFOR, QIN Li-hong, ZHANG Chun-yu, SONG Yan-tun, HAO Rong
    2021, 20(5): 1239-1249.  DOI: 10.1016/S2095-3119(20)63189-6
    Abstract ( )   PDF in ScienceDirect  
    Brassica napus L. (B. napus) is an important oil crop worldwide and it rapidly accumulates oil at late stage of seed maturation. However, little is known about the cellular mechanism of oil accumulation and seed color changes during the late stage of rapeseed development.  Here, we analyzed the ultrastructure of seed coat, aleurone and cotyledon in embryos of B. napus from 25 to 70 days after flowering (DAF).  The pigments, which were deposited on the cell wall of palisade cells in seed coat, determined dark black color of rapeseed.  The chloroplasts degenerated into non-photosynthetic plastids which caused the green cotyledon to turn into yellow.  The chloroplasts in aleurone and cotyledon cells respectively degenerated into remnants without inner and outer envelope membranes and ecoplasts with intact inner and outer envelope membranes.  From 40 to 70 DAF, there were degraded chloroplasts without thylakoid, oil bodies contacting with plastids or protein bodies, big starch deposits of chloroplasts degrading into small particles then disappearing, and small endoplasmic reticulum (ER) in aleurone and cotyledon cells.  Additionally, there were decreases of chlorophyll content and dramatic increases of oil content in rapeseed.  These results suggested that the rapid oil accumulation was independent on the NADPH synthesized by photosynthesis of chloroplasts and probably utilized other sources of reductant, such as the oxidative pentose phosphate pathway during the late stage of rapeseed development.  The triacylglycerol assembly presumably utilizes the enzymes in the plastid, cytosol or oil body of cotyledon and aleurone cells.
    Effects of shading stress during the reproductive stages on photosynthetic physiology and yield characteristics of peanut (Arachis hypogaea Linn.)
    WANG Yi-bo, HUANG Rui-dong, ZHOU Yu-fei
    2021, 20(5): 1250-1265.  DOI: 10.1016/S2095-3119(20)63442-6
    Abstract ( )   PDF in ScienceDirect  
    In intercropping systems, high-positioned crops often exert shading stress on low-positioned crops, thus affecting the agronomic characteristics of the low-positioned crops.  This study determined the mechanisms of photosynthetic, physiological and yield variations among peanut cultivars under shading stress.  Four peanut cultivars, S60, C4, P12, and YS151, were grown in the field and subjected to shading stress for 77 days during reproductive stages.  S60 and P12 showed lower yield and reduced biomass accumulation than C4 and YS151 under shading stress.  Shading stress induced higher antioxidant enzyme activities in S60 and P12, relative to C4 and YS151.  Under shading stress, S60 and P12 showed a higher light-trapping capability than C4 and YS151, which was associated with changes in chlorophyll (Chl) a and b contents, and Chl a/b ratio.  The net photosynthetic rate, stomatal conductance and transpiration rates of C4 and YS151 were decreased, but the intercellular CO2 concentration increased under shading stress.  The results demonstrated that non-stomatal limiting factors decreased the photosynthetic capacity of peanut under shading stress.  The maximum photochemical efficiency of PSII (Fv/Fm) and non-photochemical quenching (NPQ) were higher in S60 and P12 than in C4 and YS151 under shading stress.  These results suggest that S60 and P12 could absorb more light energy from weak light environments for photosynthesis than C4 and YS151 and dissipate the excess energy in the form of heat to improve their light protection ability.  This study explains the inter-variety differences in shading stress tolerance in peanut and provides physiological parameters for guiding the selection of shade-tolerant cultivars.
    Transcriptomic insights into growth promotion effect of Trichoderma afroharzianum TM2-4 microbial agent on tomato plants
    ZHAO Juan, LIU Ting, LIU Wei-cheng, ZHANG Dian-peng, DONG Dan, WU Hui-ling, ZHANG Tao-tao, LIU De-wen
    2021, 20(5): 1266-1276.  DOI: 10.1016/S2095-3119(20)63415-3
    Abstract ( )   PDF in ScienceDirect  
    Plant growth promoting fungi are receiving increased attention as valuable beneficial microorganisms in crop cultivation due to their capacity to produce bioactive substances, promote plant growth and enhance immune defense functions.  In this study, a novel Trichoderma isolate, designated as TM2-4, was screened from healthy tomato rhizosphere soil and identified as Trichoderma afroharzianum.  Culture filtrate of the isolate TM2-4 displayed obvious bioactive substance production and an evident effect in promoting tomato seed germination, with hypocotyl length, radical length and vigor index increased by 28.7, 19.4 and 62.1%, respectively, after a 100-fold dilution treatment.  To assess the promotion effect and related mechanism of isolate TM2-4, the plant biological indexes and gene expression profiles of tomato plants treated with or without T. afroharzianum TM2-4 microbial agent were investigated by greenhouse pot experiment and RNA sequencing.  The results demonstrated that T. afroharzianum TM2-4 significantly promoted tomato plant growth in terms of plant height, dry weight, number of leaves per plant and root activity, through efficient colonization in the rhizosphere and root system of the plants.  Transcriptome analyses identified a total of 984 differentially expressed genes in T. afroharzianum microbial agent inoculated tomato roots, which were mainly engaged in the biological process of phytohormone homeostasis, antioxidant activity, as well as metabolic pathways including phenylpropanoid biosynthesis and glutathione metabolism.  These findings provide useful information for understanding the mechanism of isolate TM2-4 for tomato plant growth promotion, which would facilitate further development of T. afroharzianum TM2-4 microbial agent for use in vegetable crop production.
    Fingerprinting 146 Chinese chestnut (Castanea mollissima Blume) accessions and selecting a core collection using SSR markers
    NIE Xing-hua, WANG Ze-hua, LIU Ning-wei, SONG Li, YAN Bo-qian, XING Yu, ZHANG Qing, FANG Ke-feng, ZHAO Yong-lian, CHEN Xin, WANG Guang-peng, QIN Ling, CAO Qing-qin
    2021, 20(5): 1277-1286.  DOI: 10.1016/S2095-3119(20)63400-1
    Abstract ( )   PDF in ScienceDirect  
    Chinese chestnut is an important nut tree around the world.  Although the types of Chinese chestnut resources are abundant, resource utilization and protection of chestnut accessions are still very limited.  Here, we fingerprinted and determined the genetic relationships and core collections of Chinese chestnuts using 18 fluorescently labeled SSR markers generated from 146 chestnut accessions.  Our analyses showed that these markers from the tested accessions are highly polymorphic, with an average allele number (Na) and polymorphic information content (PIC) of 8.100 and 0.622 per locus, respectively.  Using these strongly distinguishing markers, we successfully constructed unique fingerprints for 146 chestnut accessions and selected seven of the SSR markers as core markers to rapidly distinguish different accessions.  Our exploration of the genetic relationships among the five cultivar groups indicated that Chinese chestnut accessions are divided into three regional type groups: group I (North China (NC) and Northwest China (NWC) cultivar groups), group II (middle and lower reaches of the Yangtze River (MLY) cultivar group) and group III (Southeast China (SEC) and Southwest China (SWC) cultivar groups).  Finally, we selected 45 core collection members which represent the most genetic diversity of Chinese chestnut accessions.  This study provides valuable information for identifying chestnut accessions and understanding the phylogenetic relationships among cultivar groups, which can serve as the basis for efficient breeding in the future.
    High density genetic map and quantitative trait loci (QTLs) associated with petal number and flower diameter identified in tetraploid rose
    YU Chao, WAN Hui-hua, Peter M. BOURKE, CHENG Bi-xuan, LUO Le, PAN Hui-tang, ZHANG Qi-xiang
    2021, 20(5): 1287-1301.  DOI: 10.1016/S2095-3119(20)63416-5
    Abstract ( )   PDF in ScienceDirect  

    Rose is one of the most important ornamental and economic plants in the world.  Modern rose cultivars are primarily tetraploid, and during meiosis, they may exhibit double reduction or preferential chromosome pairing.  Therefore, the construction of a high density genetic map of tetraploid rose is both challenging and instructive.  In this study, a tetraploid rose population was used to conduct a genetic analysis using genome sequencing.  A total of 17 382 single nucleotide polymorphism (SNP) markers were selected from 2 308 042 detected SNPs.  Combined with 440 previously developed simple sequence repeats (SSR) and amplified fragment length polymorphism (AFLP) markers, a marker dosage of 6 885 high quality markers was successfully assigned by GATK software in the tetraploid model.  These markers were used in the construction of a high density genetic map, containing the expected seven linkage groups with 6 842 markers, a total map length of 1 158.9 cM, and an average inter-marker distance of 0.18 cM.  Quantitative trait locus (QTL) analysis was subsequently performed to characterize the genetic architecture of petal number and flower diameter.  One major QTL (qpnum-3-1) was detected for petal number in three consecutive years, which explained 20.18–22.11% of the variation in petal number.  Four QTLs were detected for flower diameter; the main locus, qfdia-2-2, was identified in two consecutive years.  Our results will benefit the molecular marker-assisted breeding of modern rose cultivars.  In addition, this study provides a guide for the genetic and QTL analysis of autotetraploid plants using sequencing-based genotyping methods. 

    Plant Protection
    Identification of leaf rust resistance genes in common wheat varieties from China and foreign countries
    LIU Yuan, Takele Weldu GEBREWAHID, ZHANG Pei-pei, LI Zai-feng, LIU Da-qun
    2021, 20(5): 1302-1313.  DOI: 10.1016/S2095-3119(20)63371-8
    Abstract ( )   PDF in ScienceDirect  
    Wheat leaf rust, triggered by Puccinia triticina Eriks (Pt), is among the most important diseases of wheat worldwide.  Deploying resistant varieties against leaf rust is the most effective, environmentally-friendly and economic way to control the disease.  In the present study, 66 wheat varieties form China and foreign countries were tested with 17 Pt races for gene postulation during the seedling stage in the greenhouse.  All the varieties were also planted to identify slow rusting responses to leaf rust at the adult plant stage in Baoding and Zhoukou field trials during the 2016/2017 to 2017/2018 cropping seasons.  Moreover, 12 closely linked molecular markers to known leaf rust resistance (Lr) genes were used for assessing all the varieties.  The results of both gene postulation and molecular marker identification showed that a total of eight Lr genes, Lr1, Lr10, Lr17, Lr20, Lr26, Lr34, Lr37 and Lr46, either singly or in combination were detected in 32 varieties.  Known Lr genes were not identified in the remaining 34 varieties.  Seventeen varieties were found to have slow rusting resistance.  The resistance sources identified in this study can be used as resources for resistance against leaf rust in wheat breeding programs in China and the respective foreign countries.
    Jasmonic acid and ethylene signaling pathways participate in the defense response of Chinese cabbage to Pectobacterium carotovorum infection
    CHEN Chang-long, YUAN Fang, LI Xiao-ying, MA Rong-cai, XIE Hua
    2021, 20(5): 1314-1326.  DOI: 10.1016/S2095-3119(20)63267-1
    Abstract ( )   PDF in ScienceDirect  
    Chinese cabbage (Brassica rapa subsp. pekinensis) suffers from soft rot disease caused by Pectobacterium carotovorum (Pc).  To uncover the mechanisms underlying the defense response of Chinese cabbage to Pc, we constructed a suppression subtractive hybridization (SSH) library from Pc-infected cabbage and obtained 1 919 non-redundant expressed sequence tags (ESTs), which were used for cDNA microarray.  We detected 800 differentially expressed genes (DEGs) in cabbage at different time points post-Pc inoculation, which were further confirmed by quantitative real-time PCR.  One quarter of these DEGs were involved in the biotic stress pathways visualized by MapMan.  Among them, 8, 8, 1, 3, and 2 DEGs were related to jasmonic acid (JA), ethylene (ET), JA+ET, auxin, and abscisic acid (ABA) signaling pathways, respectively, while no DEG was detected for salicylic acid (SA) signaling.  Assessment of phytohormone production in the Pc-infected leaves showed that JA and ET production was increased, while SA production was decreased.  Treatment with JA, methyl jasmonate (MeJA), the ET precursor 1-aminocyclopropane-1-carboxylate (ACC), or combinations thereof, reduced the disease severity, and the JA and JA+ACC treatments were superior and performed equally well.  Our findings suggest that JA and ET may act synergistically against Pc infection in Chinese cabbage, and JA-mediated signaling might be the most significant. 
    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
    Abstract ( )   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.
    Effect of a near-zero magnetic field on development and flight of oriental armyworm (Mythimna separata)
    YAN Meng-meng, ZHANG Lei, CHENG Yun-xia, Thomas W. SAPPINGTON, PAN Wei-dong, JIANG Xing-fu
    2021, 20(5): 1336-1345.  DOI: 10.1016/S2095-3119(20)63287-7
    Abstract ( )   PDF in ScienceDirect  
    The geomagnetic field affects all living organisms on the Earth.  In this study we investigated the developmental and behavioral effects of rearing Mythimna separata in a near-zero magnetic field (<500 nT) compared to the local geomagnetic field (approximately 50 μT).  The near-zero magnetic field produced by a Helmholtz coil system significantly lengthened larval and pupal development durations, increased male longevity, and reduced pupal weight, female reproduction, and the relative expression level of the vitellogenin (Vg) gene in newly emerged females.  Moreover, the near-zero magnetic field had a considerable negative effect on the mating ratio of M. separata adults.  In addition, the moths in the near-zero magnetic field displayed less flight activity late in the night than those in the Earth’s normal geomagnetic field, indicating that the flight rhythm of M. separata may be affected by the near-zero magnetic field.  Reduction in magnetic field intensity may have negative effects on the development and flight of oriental armyworm, with consequent additional effects on its migration.
    Animal Science · Veterinary Medicine
    circRNA landscape of non-pregnant endometrium during the estrus cycle in dairy goats
    LIU Xiao-rui, ZHANG Lei, CUI Jiu-zeng, YANG Li-chun, HAN Jin-cheng, CHE Si-cheng, CAO Bin-yun, LI Guang, SONG Yu-xuan
    2021, 20(5): 1346-1358.  DOI: 10.1016/S2095-3119(20)63464-5
    Abstract ( )   PDF in ScienceDirect  
    Endometrial development is a complicated process involving numerous regulatory factors.  Circular RNAs (circRNAs) have been known as a member of the naturally occurring non-coding RNA family, and are reportedly crucial for a variety of physiological processes.  This study investigated the circRNA landscape of non-pregnant endometrium of dairy goats during estrus.  Non-pregnant endometrial samples of goats at estrus day 5 (Ed5) and estrus day 15 (Ed15) were used to methodically analyze the circRNA landscape using strand-specific Ribo-Zero RNA-Seq.  A total of 2 331 differentially expressed (P<0.05) circRNAs (DEciRs) between Ed5 and Ed15 were discovered in the goat endometrium.  It was found that Nipped-B-like (NIPBL) and calcium responsive transcription factor (CARF) may participate in the development of the endometrium by decreasing (P<0.05) the levels of their circRNA-transcript forms.  Furthermore, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of DEciR host genes (hgDEciRs) revealed that tight junctions and GTPases may be involved in endometrial development during the estrus cycle.  A total of 2 331 DEciRs were discovered in the endometrium at Ed5 and Ed15.  Based on GO and KEGG enrichment analyses, it could be inferred that tight junctions and GTPases are likely to play an important role in the development of goat endometrium during the estrus cycle.  This circRNA study greatly enhances our knowledge of global trends in the development of non-pregnant endometrium during the estrus cycle in goats; these results help us to better understand the molecular regulation of endometrial development in dairy goats.
    Exploring the genetic features and signatures of selection in South China indigenous pigs
    DIAO Shu-qi, XU Zhi-ting, YE Shao-pan, HUANG Shu-wen, TENG Jin-yan, YUAN Xiao-long, CHEN Zan-mou, ZHANG Hao, LI Jia-qi, ZHANG Zhe
    2021, 20(5): 1359-1371.  DOI: 10.1016/S2095-3119(20)63260-9
    Abstract ( )   PDF in ScienceDirect  
    To explore the genetic features and signatures of selection in indigenous pigs from South China and Duroc pigs, 259 pigs from six populations were genotyped using single-nucleotide polymorphism (SNP) BeadChips.  Principal component analysis (PCA), effective population size (Ne), linkage disequilibrium (LD), and signatures of selection were explored and investigated among the six pig populations.  The results showed the Ne of five South China indigenous pig populations has been decreasing rapidly since 100 generations ago.  The LD between pairwise SNP distance at 100 kb ranged from 0.16 to 0.20 for the five indigenous pig populations, while it was 0.32 for the Duroc population.  However, the LD of all six pig populations showed the opposite order at long distances (>5 Mb).  Furthermore, 15 potential signatures of selection associated with meat quality and age at puberty were exclusively detected in South China indigenous pigs, while eight potential signatures of selection associated with growth traits were detected in Duroc pigs.  Our work provides valuable insights for the utilization and conservation of South China indigenous pigs.
    An improved scheme for infectious bursal disease virus genotype classification based on both genome-segments A and B
    WANG Yu-long, FAN Lin-jin, JIANG Nan, GAO Li, LI Kai, GAO Yu-long, LIU Chang-jun, CUI Hong-yu, PAN Qing, ZHANG Yan-ping, WANG Xiao-mei, QI Xiao-le
    2021, 20(5): 1372-1381.  DOI: 10.1016/S2095-3119(20)63424-4
    Abstract ( )   PDF in ScienceDirect  
    Infectious bursal disease (IBD) is caused by infectious bursal disease virus (IBDV), which has a genome consisting of two segments of double-stranded linear RNA.  IBDVs have been traditionally divided into four phenotypes based on their pathogenicity and antigenicity, including classic, variant, very virulent, and attenuated IBDV.  With the emergences of divergent molecular characteristics of novel strains produced by continuous mutations and recombination, it is increasingly difficult to define new IBDV strains using the traditional descriptive classification method.  The most common classification scheme for IBDV with segmented genome is based solely on segment A, while the significance of segment B has been largely neglected.  In this study, an improved scheme for IBDV genotype classification based on the molecular characteristics of both VP2 (a viral capsid protein encoded by segment A) and VP1 (an RNA-dependent RNA polymerase protein encoded by segment B) was proposed for the first time.  In this scheme, IBDV was classified into nine genogroups of A and five genogroups of B, respectively; the genogroup A2 was further divided into four lineages.  The commonly used phenotypic classifications of classic, variant, very virulent, and attenuated IBDVs correspond to the A1B1, A2B1, A3B2, and A8B1 genotypes of the proposed classification scheme.  The novel variant IBDVs including the strains identified in this study were classified as belonging to genotype A2dB1.  The flexibility and versatility of this improved classification scheme will allow the unambiguous identification of existing and emerging IBDV strains, which will greatly facilitate molecular epidemiology studies of IBDV.
    Agricultural Economics and Management
    The river chief system and agricultural non-point source water pollution control in China
    ZHOU Li, LI Ling-zhi, HUANG Ji-kun
    2021, 20(5): 1382-1395.  DOI: 10.1016/S2095-3119(20)63370-6
    Abstract ( )   PDF in ScienceDirect  
    As part of their efforts to control water pollution, local governments in China introduced the river chief system, whereby a named individual undertakes responsibility for protecting a specified waterway.  As one of the most prominent sources of water pollution, agricultural non-point-source (NPS) pollution is becoming increasingly serious.  Determining whether the river chief system, an institutional reform in China’s decentralized environmental regulation regime, is effective in alleviating NPS pollution is important for the realization of green development.  The effect of the river chief system on reducing agricultural NPS pollution is explored in this study using panel data from 308 Chinese counties during the period from 2004 to 2015.  The results reveal that the negative impact of manure output from animal breeding operations on surface water quality is reduced with the implementation of the river chief system.  However, the river chief system is ineffective in dealing with the water pollution caused by fertilizer use.  Furthermore, in the current system, cooperation among river chiefs only occurs within a province.  Local governments should increase their efforts in reducing fertilizer source loads and preventing fertilizer loads from entering surface waters.  In addition, the central government should improve cooperation among the river chiefs in upstream and downstream provinces.
    Can harvest outsourcing services reduce field harvest losses of rice in China?
    QU Xue, Daizo KOJIMA, Yukinaga NISHIHARA, WU La-ping, Mitsuyoshi ANDO
    2021, 20(5): 1396-1406.  DOI: 10.1016/S2095-3119(20)63263-4
    Abstract ( )   PDF in ScienceDirect  
    The purpose of this study is to quantify the rice harvest losses in China and to evaluate the impacts of machinery and harvest outsourcing services on these losses, given the background of high-speed mechanization and outsourcing services.  Data were collected from a national survey conducted in 2016 by the research team in conjunction with the Research Center for the Rural Economy of the Ministry of Agriculture and Rural Affairs of China.  A non-parametric method was used to test whether combine harvesting and outsourcing services could significantly reduce harvest losses.  Next, quantile regression was used to estimate the real effects of machinery and outsourcing services on harvest losses.  The analysis yielded four main study outcomes.  First, the harvest loss rate of rice in China was 3.65%.  Second, mechanical reaping and winnowing caused greater losses than manual methods, while the opposite was true of field transportation.  Third, combine harvesting increased the losses.  Fourth, the effects of an outsourcing service on losses differed among the different harvesting methods.  Outsourcing services increased losses in segmented harvesting but they reduced losses in combine harvesting.