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2020 Vol. 19 No. 8 Previous Issue    Next Issue

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Review
Crop Science
Horticulture
Plant Protection
Animal Science · Veterinary Medicine
Agro-ecosystem & Environment


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Rhododendron fortunei has beautiful flowers with bright colors showing high ornamental value and economic potential in the flower industry. Polyploid plants usually show superiority in growth, disease resistance, and adaption over their diploid relatives. The cover photo shows the seedlings of R. fortunei treated with different concentrations of oryzalin. This illustration was provided by Dr. Lin Erpei from Zhejiang A&F University. See pages 2016–2026 for more details.


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Review

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Research progress on the mechanism of improving peanut yield by single-seed precision sowing ZHANG Jia-lei, GENG Yun, GUO Feng, LI Xin-guo, WAN Shu-bo 2020, 19(8): 1919-1927.  DOI: 10.1016/S2095-3119(19)62763-2 Abstract ( )   PDF in ScienceDirect   The contradiction between the supply and demand of edible vegetable oil in China is prominent, and the self-sufficiency rate is less than 35%.  Peanut has a very outstanding status in ensuring the security of edible oil and food.  The emphasis of increasing peanut yield should be the improvement of pod yield per unit area, because the total yield of peanut has not increased as required.  This is attributed to mainly two factors - low increase in the crop productivity and the competition for land for grain and cotton crops.  For traditional double-seed sowing pattern, it is difficult to further increase the peanut yield due to the serious contradiction between populations and individuals and the declining population quality under high-yield conditions.  Single-seed precision sowing was proven to be a new way to increase the economic coefficient (economic yield/biological yield) with the basic stability of the total biomass, which could make plants distribute evenly, reduce the competition among individuals and attain the full production potential of single plant.  In order to reveal the mechanism of increasing peanut yield by single-seed precision sowing, the effects on the ontogenetic development (plant character, physiological characteristic and nutrient utilization) and population structure (population uniformity and photosynthesis, source-sink relationship and yield composition) were systematically expounded.  This study reports establishment of the high-yield cultivation technology system with the key technology of single-seed precision sowing and the supporting technology of fertilizing and management.  We anticipate its wider application for the improvement of peanut yield.

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Alphaherpesvirus-vectored vaccines against animal diseases: Current progress HU Yang, WANG Ming-shu, CHENG An-chun, JIA Ren-yong, YANG Qiao, WU Ying, LIU Ma-feng, ZHAO Xin-xin, ZHU De-kang, CHEN Shun, ZHANG Sha-qiu, WANG Yin, GAO Qun, OU Xu-min, MAO Sai, WEN Xing-jian, XU Zhi-wen, CHEN Zheng-li, ZHU Ling, LUO Qi-hui, TIAN Bin, PAN Lei-chang, Mujeeb Ur REHMAN, LIU Yun-ya, YU Yan-ling, ZHANG Ling, CHEN Xiao-yue 2020, 19(8): 1928-1940.  DOI: 10.1016/S2095-3119(20)63175-6 Abstract ( )   PDF in ScienceDirect   Recombinant virus-vectored vaccines are novel agents that can effectively activate specific and nonspecific immunity, are multivalent and multieffective, and have high safety ratings.  Animal alphaherpesviruses have a large genome, contain multiple nonessential regions that do not affect viral replication and are capable of accepting the insertion of an exogenous gene and expressing the antigen protein.  Furthermore, animal alphaherpesviruses have a wide host spectrum, can replicate in the host and continuously stimulate the animal to produce immunity to the corresponding pathogen, thus making them ideal carriers for recombinant virus-vectored vaccines.  With the development of gene-editing technology, recombinant viruses capable of expressing foreign genes can be constructed by various methods.  Currently, studies on recombinant virus-vectored vaccines constructed based on animal alphaherpesviruses have involved poultry, pigs, cattle, sheep, and companion animals.  Studies have shown that the construction of recombinant animal alphaherpesviruses enables the acquisition of immunity to multiple diseases.  This article mainly summarizes the current progress on animal alphaherpesvirus-vectored vaccines, aiming to provide reference for the development of new animal alphaherpesvirus-vectored vaccines.

Crop Science

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The breeding of japonica rice in northern China: An 11-year study (2006–2016) CUI Yue, ZHU Meng-meng, XU Zheng-jin, CHEN Wen-fu 2020, 19(8): 1941-1946.  DOI: 10.1016/S2095-3119(19)62799-1 Abstract ( )   PDF in ScienceDirect   The world’s population is facing food shortages due to climate change and the competition for arable land between food and energy crops.  Many national and international projects to develop “super rice” cultivars were established in recent decades to attain a ‘third leap forward’ in rice production.  In order to evaluate the breeding process in northern China, an 11-year tracking survey of japonica rice breeding, which involved a total of 520 rice accessions and 67 test plots, was completed in this study.  The results showed that the yields of these accessions had increased stably, which was similar to control check varieties (CKs).  The breeding strategy reduced the panicle number and increased the grain number per panicle through an increase of spikelet density (number of grains per centimeter on the panicle).  This high spikelet density benefits not only the yield but also the blast resistance and amylose content.  At higher latitudes, the preferred rice accessions had slim grain shape and extended growth period.  In the middle latitudes among the test plots, the breeders focused on reducing the amylose content to improve the cooking quality of the rice accessions.  Yield and blast resistance were the two highest priorities during the breeding selection process.  The present study evaluated the breeding process in northern China during the last decade, which may lead to new insights into the future of rice breeding.

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Quantitative trait loci analysis for root traits in synthetic hexaploid wheat under drought stress conditions LIU Rui-xuan, WU Fang-kun, YI Xin, LIN Yu, WANG Zhi-qiang, LIU Shi-hang, DENG Mei, MA Jian, WEI Yu-ming, ZHENG You-liang, LIU Ya-xi 2020, 19(8): 1947-1960.  DOI: 10.1016/S2095-3119(19)62825-X Abstract ( )   PDF in ScienceDirect   Synthetic hexaploid wheat (SHW), possesses numerous genes for drought that can help breeding for drought-tolerant wheat varieties.  We evaluated 10 root traits at seedling stage in 111 F9 recombinant inbred lines derived from a F2 population of a SHW line (SHW-L1) and a common wheat line, under normal (NC) and polyethylene glycol-simulated drought stress conditions (DC).  We mapped quantitative trait loci (QTLs) for root traits using an enriched high-density genetic map containing 120 370 single nucleotide polymorphisms (SNPs), 733 diversity arrays technology markers (DArT) and 119 simple sequence repeats (SSRs).  With four replicates per treatment, we identified 19 QTLs for root traits under NC and DC, and 12 of them could be consistently detected with three or four replicates.  Two novel QTLs for root fresh weight and root diameter under NC explained 9 and 15.7% of the phenotypic variation respectively, and six novel QTLs for root fresh weight, the ratio of root water loss, total root surface area, number of root tips, and number of root forks under DC explained 8.5–14% of the phenotypic variation.  Here seven of eight novel QTLs could be consistently detected with more than three replicates.  Results provide essential information for fine-mapping QTLs related to drought tolerance that will facilitate breeding drought-tolerant wheat cultivars.

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Characterization and map-based cloning of miniature2-m1, a gene controlling kernel size in maize GUAN Hai-ying, DONG Yong-bin, LU Shou-ping, LIU Tie-shan, HE Chun-mei, LIU Chun-xiao, LIU Qiang, DONG Rui, WANG Juan, LI Yu-ling, QI Shi-jun, WANG Li-ming 2020, 19(8): 1961-1973.  DOI: 10.1016/S2095-3119(19)62797-8 Abstract ( )   PDF in ScienceDirect   Kernel development plays an important role in determining kernel size in maize.  Here we present the cloning and characterization of a maize gene, nitrate transporter1.5 (NRT1.5), which controls small kernel phenotype by playing an important role in kernel development.  A novel recessive small kernel mutant miniature2-m1 (mn2-m1) was isolated from self-pollinated progenies of breeding materials.  The mutant spontaneously showed small kernel character arresting both embryo and endosperm development at an early stage after pollination.  Utilizing 21 polymorphic SSR markers, the mn2-m1 locus was limited to a 209.9-kb interval using 9 176 recessive individuals of a BC1 segregating population from mn2-m1/B73.  Only one annotated gene was located in this 209.9 kb region, Zm00001d019294, which was predicted to encode nitrate transporter1.5 (NRT1.5).  Allelism tests confirmed that mn2-m1 was allelic to miniature2-m2 (mn2-m2) and miniature2-710B (mn2-710B).  The mn2-m1 and mn2-m2 alleles both had nucleotide deletions in the coding region resulting in premature termination, and the mn2-710B allele had some missence mutations.  Subcellular localization showed that Miniature 2 (MN2) is localized in the plasma membrane.  Quantitative real-time PCR (qRT-PCR) analysis revealed that the expression of MN2 and some genes involved in the basal endosperm transfer layer (BETL) and embryo surrounding region (ESR) development were affected in mn2-m1 seeds.  These results suggested that MN2 plays an important role in maize seed development.

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Unraveling waterlogging tolerance-related traits with QTL analysis in reciprocal intervarietal introgression lines using genotyping by sequencing in rapeseed (Brassica napus L.) DING Xiao-yu, XU Jin-song, HUANG He, QIAO Xing, SHEN Ming-zhen, CHENG Yong, ZHANG Xue-kun 2020, 19(8): 1974-1983.  DOI: 10.1016/S2095-3119(19)62783-8 Abstract ( )   PDF in ScienceDirect   Soil waterlogging is a major environmental stress that suppresses the growth and productivity of rapeseed (Brassica napus L.).  Natural genetic variations in waterlogging tolerance (WT) were observed but no QTL mapping has been done for WT related traits in rapeseed. In this study, QTL associated with three WT related traits including relative root length (RRL), relative hypocotyl length (RHL) and relative fresh weight (RFW) were dissected using a set of reciprocal introgression lines (ILs) derived from the cross GH01×ZS9, which showed significant difference in WT.  Genotyping-by-sequencing (GBS) of the populations were performed, totally 1 468 and 1 450 binned SNPs were identified for GIL (GH01 as the recurrent parent) and ZIL (ZS9 as the recurrent parent) population, respectively.  A total of 66 distinct QTLs for WT at the seedling establishment stage including 31 for RRL, 17 for RHL and 18 for RFW were detected.  Among the 66 QTLs, 20 (29.4%) QTLs were detected in both genetic backgrounds and then they were integrated into six QTL clusters, which can be targeted in rapeseed breeding for improvement of WT through marker-assisted selection (MAS).  Based on the physical positions of SNPs and the functional annotation of the Arabidopsis thaliana genome, 56 genes within the six QTL cluster regions were selected as preliminary candidate genes, then the resequencing and transcriptome information about parents were applied to narrow the extent of candidate genes.  Twelve genes were determined as candidates for the six QTL clusters, some of them involved in RNA/protein degradation, most of them involved in oxidation-reduction process.  These findings provided genetic resources, candidate genes to address the urgent demand of improving WT in rapeseed breeding.

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Heat stability of winter wheat depends on cultivars, timing and protective methods LI Qiang, CHANG Xu-hong, MENG Xiang-hai, LI Ding, ZHAO Ming-hui, SUN Shu-luan, LI Hui-min, QIAO Wen-chen 2020, 19(8): 1984-1997.  DOI: 10.1016/S2095-3119(19)62760-7 Abstract ( )   PDF in ScienceDirect   Heat stress negatively affects wheat production in many regions of the world.  At present, sensitivity to heat stress remains one of the least understood aspects of wheat genetics and breeding, and measures for preventing heat stress are understudied. In this study, we used three cultivars of winter wheat (GY2018, SL02-1 and SY20) to evaluate the effect of heat stress at different days after anthesis (DAA) on yield and quality.  Heat stability of the cultivars were analyzed and evaluated for the effects of two kinds of regulators on wheat under heat stress conditions.  Heat treatment at 7 DAA led to the most substantial reduction in yield while GY2018 had the best heat stability with respect to yield, and demonstrated the most positive effects on several quality traits including protein content, sedimentation volume and glutenin and gliadin contents.  Heat treatment at 14 DAA had the least reduction in yield, while SY20 had the best heat stability with respect to yield and heat treatment had minimal effects on quality.  Heat treatment at 21 DAA had only a limited effect on yield, while SL02-1 had the best heat stability with respect to yield, but it showed the most negative effects on quality.  Stable time at 14 DAA and protein content at 21 DAA can be used as indicators for detecting the stability of quality under heat stress.  Among the three studied cultivars, SY20 was the most sensitive to heat stress with the stable time decreasing from 26.4 to 9.1 min, a higher sedimentation volume at 7 DAA, and a lower γ-gliadin content which increased 2.4-fold under high-temperature treatment.  The addition of various regulators had different effects: potassium dihydrogen phosphate (KDP) was more protective of yield with heat stress at 7 DAA, while Duntianbao (DTB) had better effects on quality with heat stress at 21 DAA.

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Detection and enumeration of wheat grains based on a deep learning method under various scenarios and scales WU Wei, YANG Tian-le, LI Rui, CHEN Chen, LIU Tao, ZHOU Kai, SUN Cheng-ming, LI Chun-yan, ZHU Xin-kai, GUO Wen-shan 2020, 19(8): 1998-2008.  DOI: 10.1016/S2095-3119(19)62803-0 Abstract ( )   PDF in ScienceDirect   Grain number is crucial for analysis of yield components and assessment of effects of cultivation measures.  The grain number per spike and thousand-grain weight can be measured by counting grains manually, but it is time-consuming, tedious and error-prone.  Previous image processing algorithms cannot work well with different backgrounds and different sizes.  This study used deep learning methods to resolve the limitations of traditional image processing algorithms.  Wheat grain image datasets were collected in the scenarios of three varieties, six background and two image acquisition devices with different heights, angles and grain numbers, 1 748 images in total.  All images were processed through color space conversion, image flipping and rotation.  The grain was manually annotated, and the datasets were divided into training set, validation set and test set.  We used the TensorFlow framework to construct the Faster Region-based Convolutional Neural Network Model.  Using the transfer learning method, we optimized the wheat grain detection and enumeration model.  The total loss of the model was less than 0.5 and the mean average precision was 0.91.  Compared with previous grain counting algorithms, the grain counting error rate of this model was less than 3% and the running time was less than 2 s.  The model can be effectively applied under a variety of backgrounds, image sizes, grain sizes, shooting angles, and shooting heights, as well as different levels of grain crowding.  It constitutes an effective detection and enumeration tool for wheat grain.  This study provides a reference for further grain testing and enumeration applications.

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The influence of drought stress on malt quality traits of the wild and cultivated barleys HONG Ye, ZHANG Guo-ping 2020, 19(8): 2009-2015.  DOI: 10.1016/S2095-3119(19)62794-2 Abstract ( )   PDF in ScienceDirect   As a major abiotic stress, drought causes instability and deterioration of malt barley quality.  There is distinct difference among barley cultivars in the responses of the main malt quality traits to drought stress.  In the previous study, we identified some Tibetan wild barley accessions with relatively less change of malt quality traits under drought.  In this study, we examined the impact of drought stress during grain filling stage on grain weight and several important malt quality traits, including total protein content, β-glucan content, limit dextrinase activity, β-amylase activity, and protein fractions in four barley genotypes (two Tibetan wild accessions and two cultivars).  Drought treatment reduced grain weight, β-glucan content, and increased total protein content, β-amylase activity.  These changes differed among barley genotypes and treatments, and are closely associated with grain filling process and kernel weight.  All the results indicated Tibetan wild barley had great potential for developing drought tolerant barley cultivars.  Relatively stable kernel weight or filling process under water stress should be highlighted in malt barley breeding in order to reduce the effect of water stress on malt barley quality.

Horticulture

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Induction and characterization of polyploids from seeds of Rhododendron fortunei Lindl. MO Lan, CHEN Jun-hao, CHEN Fei, XU Qiang-wei, TONG Zai-kang, HUANG Hua-hong, DONG Ren-hui, LOU Xiong-zhen, LIN Er-pei 2020, 19(8): 2016-2026.  DOI: 10.1016/S2095-3119(20)63210-5 Abstract ( )   PDF in ScienceDirect   Most Rhododendron species are ornamental flowering species widely distributed in Asia, North America, and West Europe.  Rhododendron fortunei, one of the endemic Rhododendron species in China, has beautiful flowers with bright colors and is being exploited to meet the needs of the flower market.  Polyploid plants usually show superiority in growth, disease resistance, and adaption over their diploid relatives.  Here, we report the first case of polyploid induction in R. fortunei.  In order to induce polyploidy in R. fortunei, germinating seeds were treated with different concentrations of oryzalin for 16 h.  By evaluating ploidy level with flow cytometry, a total of 34 polyploid R. fortunei lines, including 27 tetraploid lines and seven octoploid lines, were obtained.  A comparison of treatments indicated that 7.5 mg L–1 oryzalin was the optimal concentration for polyploid induction in seeds of R. fortunei.  Compared with diploid plants, tetraploid and octoploid plants exhibited slower growth rates and had thicker and rounder curled leaves with more leaf epidermal hairs.  Moreover, larger stomata at lower density were also observed in the leaves of polyploid plants.  Chlorophyll contents were also significantly increased in polyploid plants, which leads to a darker green leaf color.  Both small and large individuals exhibiting the same characteristics were observed among the obtained tetraploid plants.  Overall, our study establishes a feasible method for polyploid induction in R. fortunei, thus providing a basis for breeding new R. fortunei varieties.

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The effect of artificial solar spectrum on growth of cucumber and lettuce under controlled environment ZOU Jie, ZHOU Cheng-bo, XU Hong, CHENG Rui-feng, YANG Qi-chang, LI Tao 2020, 19(8): 2027-2034.  DOI: 10.1016/S2095-3119(20)63209-9 Abstract ( )   PDF in ScienceDirect   Light-emitting diodes (LEDs) have been widely applied in the controlled environment agriculture, which are characterized by relatively narrow-band spectra and energetical efficiency.  Most recently, the spectrum of Sunlike LEDs has been engineered and it closely resembles solar spectrum in the range of photosynthetic active radiation (PAR, 400–700 nm).  To investigate how plant growth responses to the spectrum of Sunlike LEDs, cucumber and lettuce plants were cultivated and their responses were compared with the conventional white LEDs as well as composite of red and blue LEDs (RB, R/B ratio was 9:1).  We observed that although Sunlike LEDs resulted in a longer stem in cucumber, dry weight and leaf area were similar as those under RB LEDs, and significantly higher than those under white LEDs.  Moreover, cucumber leaves grown under Sunlike and white LEDs showed higher photosynthetic capacity than those grown under RB LEDs.  For lettuce, plants grown under Sunlike LEDs showed larger leaf area and higher dry weight than the other two treatments.  However, the leaf photosynthetic capacity of lettuce grown under Sunlike LEDs was the lowest.  In this context, the spectrum induced plant functions are species-dependent.  Furthermore, the three types of LEDs show distinct light spectra and they are different in many aspects.  Therefore, it is difficult to attribute the different plant responses to certain specific light spectra.  We conclude that plants grown under Sunlike LEDs exhibit larger leaf area, which may be due to some specific spectrum distributions (such as more far-red radiation), and consequently are favorable for light interception and therefore result in greater production.

Plant Protection

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Genome-wide association analysis for stripe rust resistance in spring wheat (Triticum aestivum L.) germplasm Sher MUHAMMAD, Muhammad SAJJAD, Sultan Habibullah KHAN, Muhammad SHAHID, Muhammad ZUBAIR, Faisal Saeed AWAN, Azeem Iqbal KHAN, Muhammad Salman MUBARAK, Ayesha TAHIR, Muhammad Umer, Rumana KEYANI, Muhammad Inam AFZAL, Irfan MANZOOR, Javed Iqbal WATTOO, Aziz-ur REHMAN 2020, 19(8): 2035-2043.  DOI: 10.1016/S2095-3119(19)62841-8 Abstract ( )   PDF in ScienceDirect   Stripe rust is a continuous threat to wheat crop all over the world.  It causes considerable yield losses in wheat crop every year.  Continuous deployment of adult plant resistance (APR) genes in newly developing wheat cultivars is the most judicious strategy to combat this disease.  Herein, we dissected the genetics underpinning stripe rust resistance in Pakistani wheat germplasm.  An association panel of 94 spring wheat genotypes was phenotyped for two years to score the infestation of stripe rust on each accession and was scanned with 203 polymorphic SSRs.  Based on D´ measure, linkage disequilibrium (LD) exhibited between loci distant up to 45 cM.  Marker-trait associations (MTAs) were determined using mixed linear model (MLM).  Total 31 quantitative trait loci (QTLs) were observed on all 21 wheat chromosomes.  Twelve QTLs were newly discovered as well as 19 QTLs and 35 previously reported Yr genes were validated in Pakistani wheat germplasm.  The major QTLs were QYr.uaf.2AL and QYr.uaf.3BS (PVE, 11.9%).  Dissection of genes from the newly observed QTLs can provide new APR genes to improve genetic resources for APR resistance in wheat crop.

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The M43 domain-containing metalloprotease RcMEP1 in Rhizoctonia cerealis is a pathogenicity factor during the fungus infection to wheat PAN Li-jun, LU Lin, LIU Yu-ping, WEN Sheng-xian, ZHANG Zeng-yan 2020, 19(8): 2044-2055.  DOI: 10.1016/S2095-3119(19)62874-1 Abstract ( )   PDF in ScienceDirect   Wheat (Triticum aestivum L.) is an important staple crop for global human.  The necrotrophic fungus Rhizoctonia cerealis is the causal pathogen of sharp eyespot, a devastating disease of wheat.  Herein, we identified RcMEP1, a zinc metalloprotease-encoding gene from R. cerealis genomic sequences, and characterized its pathogenesis function.  RcMEP1 expressed at markedly-high levels during R. cerealis infection process to wheat.  The predicted protein RcMEP1 comprises of 287 amino acid residues and contains a signal peptide and a M43 metalloprotease domain harboring the active site motif (HEVGHWLGLYH).  The assays of Agrobacterium tumefaciens-mediated transient expression in Nicotiana benthamiana leaves indicated that RcMEP1 is an apoplastic elicitor of cell death, and that the predicted signal peptide functions and is required for secretion and cell death-induction.  The purified RcMEP1 protein and its M43 domain peptide were individually able to induce plant cell death and H2O2 accumulation, and to inhibit expression of host chitinases when infiltrated into wheat and N. benthamiana leaves, while the M43 domain-deleting peptide and negative control lacked the capacity.  Moreover, compared with the control pretreatment, the purified RcMEP1 protein or its M43-domain peptide resulted in enhanced pathogenesis in the inoculated wheat, whereas the M43 domain-deleting peptide failed.  These results suggest that RcMEP1 acted as an important pathogenicity factor during R. cerealis infection to wheat and that its signal peptide and M43 domain are required for the secretion and pathogenesis of RcMEP1.  This study provides insights into pathogenesis role of M43 domain-containing metalloproteases during R. cerealis infection to wheat.

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A LAMP-assay-based specific microbiota analysis reveals community dynamics and potential interactions of 13 major soybean root pathogens YE Wen-wu, ZENG Dan-dan, XU Miao, YANG Jin, MA Jia-xin, WANG Yuan-chao, ZHENG Xiao-bo 2020, 19(8): 2056-2063.  DOI: 10.1016/S2095-3119(19)62855-8 Abstract ( )   PDF in ScienceDirect   Soybean root diseases are associated with numerous fungal and oomycete pathogens; however, the community dynamics and interactions of these pathogens are largely unknown.  We performed 13 loop-mediated isothermal amplification (LAMP) assays that targeted specific soybean root pathogens, and traditional isolation assays.  A total of 159 samples were collected from three locations in the Huang-Huai-Hai region of China at three soybean growth stages (30, 60, and 90 days after planting) in 2016.  In LAMP results, we found that pathogen communities differed slightly among locations, but changed dramatically between soybean growth stages.  Phytophthora sojae, Rhizoctonia solani, and Fusarium oxysporum were most frequently detected at the early stage, whereas Phomopsis longicolla, Fusarium equiseti, and Fusarium virguliforme were most common in the later stages.  Most samples (86%) contained two to six pathogen species.  Interestingly, the less detectable species tended to exist in the samples containing more detected species, and some pathogens preferentially co-occurred in diseased tissue, including P. sojae–R. solani–F. oxysporum and F. virguliforme–Calonectria ilicicola, implying potential interactions during infection.  The LAMP detection results were confirmed by traditional isolation methods.  The isolated strains exhibited different virulence to soybean, further implying a beneficial interaction among some pathogens.

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Identification of a novel emaravirus infecting lilac through next-generation sequencing WANG Ya-qin, SONG Yu, CAO Meng-ji, CHENG Qi, WU Jian-xiang, HU Tao 2020, 19(8): 2064-2071.  DOI: 10.1016/S2095-3119(19)62806-6 Abstract ( )   PDF in ScienceDirect   Emaraviruses are multipartite negative-sense single-stranded viruses that usually infect flowering plants.  Using unbiased next-generation sequencing (NGS) approach, a novel virus from lilac leaves with yellow mottle symptom was identified.  Five viral genomic RNA segments were detected and completely sequenced.  The molecular characteristics of the viral RNAs and proteins resemble those of members of the genus Emaravirus.  The virus was found to be mechanically transmissible to Nicotiana benthamiana. Sequence alignment and phylogenetic analyses of the virus support the proposal of creating a new species in the genus Emaravirus for which the name lilac chlorotic ringspot-associated virus (LiCRaV) is proposed.

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Predicting the potential geographic distribution of Bactrocera bryoniae and Bactrocera neohumeralis (Diptera: Tephritidae) in China using MaxEnt ecological niche modeling Jing Wan, QI Guo-jun, MA Jun, Yonglin Ren, WANG Rui, Simon MCKIRDY 2020, 19(8): 2072-2082.  DOI: 10.1016/S2095-3119(19)62840-6 Abstract ( )   PDF in ScienceDirect   Bactrocera bryoniae and Bactrocera neohumeralis are highly destructive and major biosecurity/quarantine pests of fruit and vegetable in the tropical and subtropical regions in the South Pacific and Australia.  Although these pests have not established in China, precautions must be taken due to their highly destructive nature.  Thus, we predicted the potential geographic distribution of B.?bryoniae and B. neohumeralis across the world and in particular China by ecological niche modeling of the Maximum Entropy (MaxEnt) model with the occurrence records of these two species. Bactrocera bryoniae and B. neohumeralis exhibit similar potential geographic distribution ranges across the world and in China, and each species was predicted to be able to distribute to over 20% of the globe.  Globally, the potential geographic distribution ranges for these two fruit fly species included southern Asia, the central and the southeast coast of Africa, southern North America, northern and central South America, and Australia.  While within China, most of the southern Yangtze River area was found suitable for these species.  Notably, southern China was considered to have the highest risk of B. bryoniae and B. neohumeralis invasions.  Our study identifies the regions at high risk for potential establishment of B. bryoniae and B. neohumeralis in the world and in particular China, and informs the development of inspection and biosecurity/quarantine measures to prevent and control their invasions.

Animal Science · Veterinary Medicine

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PGC-1α differentially regulates the mRNA expression profiles of genes related to myofiber type specificity in chicken SHAN Yan-ju, JI Gai-ge, ZOU Jian-min, ZHANG Ming, TU Yun-jie, LIU Yi-fan, JU Xiao-jun, SHU Jing-ting 2020, 19(8): 2083-2094.  DOI: 10.1016/S2095-3119(20)63177-X Abstract ( )   PDF in ScienceDirect   Previous studies on mammals showed that peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) played a prominent role in regulating muscle fiber type transition and composition.  However, the role of PGC-1α in chicken muscle has seldom been explored.  To investigate the effect of PGC-1α on chicken skeletal muscles in this study, the PGC-1α gene was overexpressed or silenced in chicken primary myoblasts by using lentivirus, and then the effects of the PGC-1α gene overexpression and knockdown on the mRNA expression profile of genes related to myofiber type specificity were examined during fiber formation.  The results showed that overexpression of PGC-1α from proliferation to differentiation was accompanied by the up-regulated expression of Pax7, MyoD, and CnAα, which was significantly (P<0.01) increased after one day of transfection (1I).  The enhancement of MyoG, MEF2c, and MyHC SM expression lagged, which was improved significantly (P<0.01) after four days of transfection (1I3D).  Overexpression of PGC-1α decreased (P<0.01) the MyHC FWM expression after four days of transfection (1I3D), and it had no significant impact (P>0.05) on the expression of CnB1, NFATc3, and MyHC FRM during myofiber formation.  The effective silence (P<0.01) of PGC-1α by lentivirus mediating short hairpin RNA (shRNA) was detected after four days of transfection (1I3D) in cultures, and the lack of its function in chicken primary myoblasts significantly (P<0.01) down-regulated the expression of Pax7, MyoD, CnAα, MyoG, MEF2c, and MyHC SM, significantly (P<0.01) up-regulated the expression of MyHC FWM, and had no significant impact (P>0.05) on the expression of CnB1, NFATc3, and MyHC FRM.  These results indicated that the role of PGC-1α in regulating the fiber type specificity of chicken skeletal muscles might be similar to that in mammals, which interplayed with key genes related to myocyte differentiation and calcineurin signaling pathway.

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Kinetics of selenium absorption in ligated small intestinal loops of chicks LIU Guo-qing, ZHANG Shu-min, AN Zhi-min, FENG Yan-zhong, DONG Xue-yu, LI Su-fen, LU Lin, ZHANG Li-yang, WANG Run-lian, LUO Xu-gang, LIAO Xiu-dong 2020, 19(8): 2095-2102.  DOI: 10.1016/S2095-3119(20)63194-X Abstract ( )   PDF in ScienceDirect   Selenium (Se) is an essential trace element that has a large number of biological functions for broilers.  However, the absorption kinetics of Se from sodium selenite in the small intestine of broilers remains unclear.  Therefore, two experiments were conducted with 28-d-old commercial male broilers to study the kinetics of Se absorption in ligated small intestinal segments.  In experiment 1, the Se absorption in duodenal, jejunal, and ileal segments at different post-perfusion time points (0, 20, 40, 60, 80, 100 and 120 min) were compared.  In experiment 2, a kinetic study of Se absorption was conducted with the duodenal, jejunal, and ileal loops perfused with solutions containing 0, 0.0375, 0.075, 0.15, 0.30, or 0.60 μg mL–1 of Se as sodium selenite, and Se contents in perfusates were determined at 100 min after perfusion.  The results from experiment 1 showed that the Se absorption increased in an asymptotic response (P<0.0001) to post-perfusion time within 120 min in all the small intestinal segments, but increased linearly (P<0.0001) at less than 100 min after perfusion in duodenal and ileal segments, while more than 96.0% of the maximum Se absorption occurred at 100 min after perfusion in each small intestinal segment.  In experiment 2, there was no difference (P>0.05) in the Se absorption rate among different ligated small intestinal segments perfused with solutions containing 0.0375–0.15 μg mL–1 of Se, however, the Se absorption rate was higher (P<0.05) in the jejunum than that in the duodenum perfused with solutions containing 0.30–0.60 μg mL–1 of Se.  The kinetic curves of Se absorption demonstrated that the Se absorption was a saturated carrier-mediated process in the duodenum, and the maximum absorption rate was 1 271 pg min–1 cm–1; whereas the Se absorptions were a non-saturated diffusion process in the jejunum and ileum, and the diffusive constants were 2 107 and 1 777 cm2 min–1, respectively.  The results from the present study indicate that the jejunum is the main Se absorption site, and the Se absorption is a saturated carrier-mediated process in the duodenum, but a non-saturated diffusion process in the jejunum and ileum of broilers.

Agro-ecosystem & Environment

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Management of rice straw with relay cropping of Chinese milk vetch improved double-rice cropping system production in southern China ZHOU Xing, LIAO Yu-lin, LU Yan-hong, Robert M. REES, CAO Wei-dong, NIE Jun, LI Mei 2020, 19(8): 2103-2115.  DOI: 10.1016/S2095-3119(20)63206-3 Abstract ( )   PDF in ScienceDirect   Improved utilization of rice (Oryza sativa L.) straw and Chinese milk vetch (Astragalus sinicus L., vetch) has positive effects on rice production.  So far, few studies have investigated the productivity of vetch under different residue management practices in double-rice cropping system.  The effects of rice straw on the growth and nutrient accumulation of vetch across seven years (2011–2017) and the subsequent effects of rice straw and vetch on two succeeding rice crops in a vetch–rice–rice cropping system, with the vetch established by relay cropping, were examined.  The seven-year double-rice experiment consisted of the following treatments: (1) 100% chemical fertilizer (F-F100); (2) only vetch without chemical fertilizer (M-Con); (3) 80% chemical fertilizer plus vetch plus a low-cutting height (low-retained stubble) with the removal of straw (M-F80); (4) 80% chemical fertilizer plus vetch plus a low-cutting height with the retention of straw (M-F80-LR); (5) 80% chemical fertilizer plus vetch plus a high-cutting height (high-retained stubble) with the retention of straw (M-F80-HR); and (6) no fertilizer (F-Con).   The yields of the two rice crops after vetch were not affected by either the cutting height of stubble with retention of straw or by the management of straw (retention vs. removal) with low-cutting height of stubble.  The yields of the two rice crops after vetch were significantly higher for M-F80-HR than for M-F80-LR, but the relative contributions of the high-cutting height and straw retention to the higher rice yield could not be determined in this study.  The yield stability of the double-rice grain in M-F80-HR was also increased, as determined by a sustainable yield index.  Significant increases in vetch biomass and nutrient uptake were observed in the fertilized treatments during the rice season compared with the unfertilized treatments.  In M-F80-HR plots, improvements in the growing environment of the vetch by conserving soil water content were associated with the highest vetch biomass, nutrient uptake, and yield stability of vetch biomass.  These increased nutrient inputs partially replaced the demand for chemical fertilizer and stimulated the rice yields.  It can be concluded that retaining higher-cutting stubble residues with straw retention could be the best straw management practice for increasing the vetch biomass and nutrient use efficiency, thereby allowing utilization of high-cutting height with retention of straw and vetch to improve the stability of rice productivity in a double-rice cropping system.

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Application of Chinese milk vetch affects rice yield and soil productivity in a subtropical double-rice cropping system CHEN Jing-rui, QIN Wen-jing, CHEN Xiao-fen, CAO Wei-dong, QIAN Guo-min, LIU Jia, XU Chang-xu 2020, 19(8): 2116-2126.  DOI: 10.1016/S2095-3119(19)62858-3 Abstract ( )   PDF in ScienceDirect   Green manure can be used as a substitute for chemical fertilizer without reducing rice yield.  We studied the responses of soil fertility and rice yield to different combinations of Chinese milk vetch (CMV; Astragalus sinicus L.) and chemical fertilizer in a subtropical double-rice cropping system.  Our goal is to reduce chemical fertilizer use and decrease environmental contamination.  Compared with the recommended rate of chemical fertilizer (CF), both early- and late-rice yields in the two treatments supplied with 15 and 22.5 Mg CMV ha–1 plus 60% CF (represented as 60A and 60B, respectively) showed no significant differences while the two treatments supplied with 30 and 37.5 Mg CMV ha–1 plus 60% CF (represented as 60C and 60D, respectively) showed significantly higher values.  The sustainable yield index (SYI) values in the 60C and 60D treatments with double-rice croppong system were significantly higher than those in other treatments (P<0.05).  Early-rice yield showed a significant positive relationship with the Chinese milk vetch incorporation rate.  The coefficients increased annually from 2009 to 2013 and then decreased in 2014.  Soil organic matter increased over time by the end of the experiment in all of the treatment groups.  Soil organic matter in 60A, 60B and 60C showed no significant difference compared with that in CF, while soil organic matter in 60D was significantly higher than that in CF.  The slopes of soil organic matter and total nitrogen over six years were the highest in 60C and 60D.  The soil total nitrogen content in 60A, 60B, 60C and 60D was higher than that in CF, but the differences were not significant (P>0.05).  Therefore, a relatively high Chinese milk vetch incorporation rate (≥30 Mg ha–1) was more effective in improving the productivity and sustainability of paddy soil.  The decreased coefficients of early-rice yield and the Chinese milk vetch incorporation rate in 2014 implied that the benefits of soil fertility and rice yield created by Chinese milk vetch input may decline after five years under a continuously high rate of Chinese milk vetch incorporation.

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A case-based method of selecting covariates for digital soil mapping LIANG Peng, QIN Cheng-zhi, ZHU A-xing, HOU Zhi-wei, FAN Nai-qing, WANG Yi-jie 2020, 19(8): 2127-2136.  DOI: 10.1016/S2095-3119(19)62857-1 Abstract ( )   PDF in ScienceDirect   Selecting a proper set of covariates is one of the most important factors that influence the accuracy of digital soil mapping (DSM).  The statistical or machine learning methods for selecting DSM covariates are not available for those situations with limited samples.  To solve the problem, this paper proposed a case-based method which could formalize the covariate selection knowledge contained in practical DSM applications.  The proposed method trained Random Forest (RF) classifiers with DSM cases extracted from the practical DSM applications and then used the trained classifiers to determine whether each one potential covariate should be used in a new DSM application.  In this study, we took topographic covariates as examples of covariates and extracted 191 DSM cases from 56 peer-reviewed journal articles to evaluate the performance of the proposed case-based method by Leave-One-Out cross validation.  Compared with a novices’ commonly-used way of selecting DSM covariates, the proposed case-based method improved more than 30% accuracy according to three quantitative evaluation indices (i.e., recall, precision, and F1-score).  The proposed method could be also applied to selecting the proper set of covariates for other similar geographical modeling domains, such as landslide susceptibility mapping, and species distribution modeling.