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    2020 Vol. 19 No. 2 Previous Issue    Next Issue

    Review
    Special focus: Potato insect pest management
    Section 1 Decoding potato insect pests
    Section 2 Invasive insect pests of potato: global perspectives
    Section 3 The interaction between potato aphids and virus
    Section 4 Integrative management strategies for potato insect pests
    Crop Science
    Horticulture
    Plant Protection
    Agricultural Economics and Management


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    Review
    Principles and practices of the photo-thermal adaptability improvement in soybean
    ZHANG Li-xin, LIU Wei, Mesfin Tsegaw, XU Xin, QI Yan-ping, Enoch Sapey, LIU Lu-ping, WU Ting-ting, SUN Shi, HAN Tian-fu
    2020, 19(2): 295-310.  DOI: 10.1016/S2095-3119(19)62850-9
    Abstract ( )   PDF in ScienceDirect  
    As a short-day (SD) and thermophilic plant, soybean (Glycine max (L.) Merr.) is sensitive to photo-thermal conditions.  This characteristic severely limits the cultivation range of a given soybean cultivar and affects the performances of agronomic traits such as yield, plant architectures, and seed quality.  Therefore, understanding the mechanism of photo-thermal sensitivity will provide a theoretical basis for soybean improvement.  In this review, we introduce the advances in physiological, genetic, and molecular researches in photoperiodism of soybean, and progress in the improvement of the photo-thermal adaptability.  We also summarize the photo-thermal conditions and characteristics of widely-planted soybean cultivars of major production regions in China.  Furthermore, we proposed a novel concept of ‘ecotyping’ and the strategies for widely-adapted soybean cultivar breeding.  This review provides an important guide for improving the adaptability of soybean.
     
    Special focus: Potato insect pest management
    Editorial - Potato insect pest management
    GAO Yu-lin, ZHOU Wen-wu
    2020, 19(2): 311-315.  DOI: 10.1016/S2095-3119(19)62852-2
    Abstract ( )   PDF in ScienceDirect  
    Having an estimated production of 388 million tons in 2017 (FAO 2019), potato is one of the world’s most important food crops, along with rice, wheat, and maize.  Potato plants can adapt to different agricultural environments and are widely grown over many latitudes and elevations (Douches et al. 2004).  In addition to its consumption in Europe, North America and countries of the former Soviet Union, potato is now also popularized in Africa and Asia, especially in the developing countries including China and India.  Since 2015, China has been boosting potato production to become the fourth major crop produced in the country following rice, wheat and maize (Zhang et al. 2017; Xu et al. 2019).  And developing potato as the staple food was also included by Ministry of Agriculture and Rural Affairs of China in its important agenda.  Further improvement of potato production globally could promote the sustainable development of agriculture and safeguard world’s food security in the near future.
    Insect pests are one of the major constraints to commercial production of potato in the world.  For over
    8 000 years since its domestication in the central Andes, the potato has been plagued by a number of serious insect pests (Radcliffe 1982).  These include some of the most prolific and adaptable species known to human.  If left uncontrolled, the insect pests can completely destroy the affected crops.  With the rapid development of international trade, many insect herbivores of crops have spread across the continents along with agricultural products, and soon outbroke and became serious pests in their colonized areas (Carrillo et al. 2019).  To deal with the potato insect pest problems, currently several issues remain to be solved: (1) Know these insect pests.  A deep decoding of the biology and ecology of the potato insect pests is the basis for developing counter-measures to them.  (2) Know how the insects come and where they will go.  Figuring out the spreading of the invasive insects of potato can help achieve a better prevention and slow down their damage risks.  (3) Know their helpers during the harm to crops.  The co-occurrence of insects and plant pathogens in potato fields requires the raveling of how they interacts.  (4) Know the integrative management strategies.  Insect management in commercial potato production is heavily reliant on synthetic backlash and causing environmental pollution, and thus new strategies are needed to achieve a more ecological control of these pests. 
    As guest editors, we are pleased to present 12 papers about the biology, ecology and management of major insect pests damaging on the potato crop in this special focus of the Journal of Integrative Agriculture.  We hope to improve our understanding of insect pests of potato and provide guidance for countries facing the IPM of those pests worldwide.  The 12 papers are organized into the following four sections.
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    Section 1 Decoding potato insect pests
    Decoding Phthorimaea operculella (Lepidoptera: Gelechiidae) in the new age of change
    Silvia I. RONDON
    2020, 19(2): 316-324.  DOI: 10.1016/S2095-3119(19)62740-1
    Abstract ( )   PDF in ScienceDirect  
    Arthropods and pathogens constantly challenge potato Solanum tuberosum L. production.  Scenarios of climate variation have increased the possibility of changes in pests’ biological and ecological patterns by increasing or reducing overwintering length, changes in population growth rates, number of generations, crop-pest relationship, and therefore affecting their expansion.  Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae) is one of the main pests affecting potatoes worldwide.  Adults oviposit single or multiple eggs in leaves, stems, and tubers, while the larvae in immature stage mine leaves or burrows into tubers turning them unmarketable.  Traditional control methods are effective in controlling P. operculella, but many factors determine the success of the control chosen.  This review provides key highlights of current information available that could be used as a resource to fight this pest. 
     
    Behavioral responses of potato tuber moth (Phthorimaea operculella) to tobacco plant volatiles
    LI Xiang, ZHANG Xiu-ge, XIAO Chun, GAO Yu-lin, DONG Wen-xia
    2020, 19(2): 325-332.  DOI: 10.1016/S2095-3119(19)62663-8
    Abstract ( )   PDF in ScienceDirect  
    Potato tuber moth (PTM) Phthorimaea operculella, also known as tobacco splitworm, is an important pest of tobacco plants.  The knowledge on the interaction of tobacco plant volatiles and PTM behavior is limited.  To clarify the effect of tobacco plant volatiles on the orientation and oviposition behaviors of PTM and to identify potential compounds for PTM control, tobacco plant volatiles were collected by headspace collection method, and volatile compounds were identified by gas chromatography-mass spectrometry.  Thirteen electrophysiological active compounds were screened by employing coupled gas chromatography-electroantennogram detection and from which nine available compounds were further verified by electroantennogram recording.  cis-3-Hexen-1-ol showed significant attractant effect on the orientation behaviors of both male and female moths.  Nonanal and decanal could only attract females, while octanal exhibited repellent effect on males.  Oviposition selection experiment indicated that nonanal, decanal, decane and methyl hexadecanoate could stimulate the gravid females to lay more eggs, while octanal and 2,6-bis(1,1-dimethylenthyl)-4-methyl phenol inhibited their oviposition.  Our study added more compounds to the list that could serve as potential PTM deterrents or attractants.
     
    Ecology and management of Bactericera cockerelli and Candidatus Liberibacter solanacearum in New Zealand
    Jessica VEREIJSSEN
    2020, 19(2): 333-337.  DOI: 10.1016/S2095-3119(19)62641-9
    Abstract ( )   PDF in ScienceDirect  
    The psyllid Bactericera cockerelli was first reported in New Zealand in 2006 and spread quickly throughout all potato growing regions.  In 2009, B. cockerelli was associated with the plant pathogenic bacterium Candidatus Liberibacter solanacearum, the putative causal agent of zebra chip disease in potato.  Both the psyllid and the bacterium have non-crop host plants which can serve as reservoirs when the crop is not available.  Growers apply different management strategies that fit integrated pest management programmes to manage B. cockerelli and subsequently lower incidence of zebra chip disease in potato crops.  Despite best management efforts, complete control of B. cockerelli and zero incidence of zebra chip disease are not achievable at the current time.
     
    Section 2 Invasive insect pests of potato: global perspectives
    Bactericera cockerelli (Sulc), a potential threat to China’s potato industry
    Oluwashola OLANIYAN, Neus RODRíGUEZ-GASOL, Nathalie CAYLA, Eleonor MICHAUD, Steve D. WRATTEN
    2020, 19(2): 338-349.  DOI: 10.1016/S2095-3119(19)62754-1
    Abstract ( )   PDF in ScienceDirect  
    The potato psyllid Bactericera cockerelli (Hemiptera: Triozidae) has recently emerged as a serious pest of potatoes and other solanaceous crops.  It causes direct feeding damage and also vectors Candidatus Liberibacter solanaceaerum (Lso), a pathogen that causes zebra chip disease in potatoes and which potentially costs growers millions of dollars each year.  Such producers rely on frequent sprays of pesticides for psyllid control but the results are unsatisfactory and there are negative side effects.  The psyllid has spread beyond its native range in southwest US and northern Mexico to Canada, El Salvador, Honduras, Guatemala and Nicaragua via medium to long range dispersal flights perhaps aided by wind currents, and through anthropogenic means.  It was accidentally introduced into New Zealand in 2006 and most recently Australia, most likely through the importation of infested plant material.  This review summarizes information from studies on the biology, impact and management of B. cockerelli, and highlights the imminent risk of this insect and its associated pathogen invading China, the world’s largest producer of fresh potatoes.  Development of risk maps leading to increased surveillance, could prevent or delay an incursion and facilitate early detection or eradication should this occur.  Long-term management with Lso-tolerant potato cultivars and psyllid control using the parasitic wasp Tamarixia triozae and other natural enemies should be pursued, rather than depending on synthetic pesticides.
    Genetic structure of the invasive Colorado potato beetle Leptinotarsa decemlineata populations in China
    YANG Fang-yuan, GUO Jian-jun, LIU Ning, ZHANG Run-zhi
    2020, 19(2): 350-359.  DOI: Received 30 August, 2018 Accepted 3 December, 201810.1016/S2095-3119(19)62600-6
    Abstract ( )   PDF in ScienceDirect  
    The Colorado potato beetle (CPB), Leptinotarsa decemlineata Say, is an infamous invasive species worldwide.  It was first found in Xinjiang Uygur Autonomous Region of China in 1993 and spread to Northeast China in 2013.  To better understand the genetic structure and the diffusion path of their populations in China, we used nine polymorphic microsatellite loci to elucidate the genetic diversity, genetic structure and gene flow among nine CPB populations across Xinjiang and Northeast China.  The results show that: (1) Two genetically separated clusters were identified by phylogenetic tree, principal coordinate analysis (PCoA) and Bayesian cluster method.  Cluster one contained populations from Xinjiang, China.  Cluster two contained populations from Northeast China.  A genetic differentiation existed between the two clusters.  (2) Three populations in Northeast China hold an obvious genetic differentiation according to the phylogenetic tree and PCoA, indicating that multiple introductions may occur in Northeast China.  (3) The Altay population in Xinjiang showed a closer genetic relationship with the populations in Northeast China which may be due to the fact that they collectively originated in neighboring Russia.  (4) Among all populations, Mulei and Wusu had obvious gene migrations from Tacheng, indicating that the inland populations are most likely to originate from Tacheng, Xinjiang.
     
    Management of Colorado potato beetle in invasive frontier areas
    WANG Cong, XU Han, PAN Xu-bin
    2020, 19(2): 360-366.  DOI: 10.1016/S2095-3119(19)62801-7
    Abstract ( )   PDF in ScienceDirect  
    Colorado potato beetle (CPB) is one of the most devastating invasive insects and it is native to North America.  It feeds on several wild species of the genus Solamum, such as S. elaeagnifolium and S. rostratum Dunal, and is one of the major pests of potato and eggplant.  Beginning in the early 19th century, CPB has rapidly spread across North America, Europe, and Central Asia.  CPB was first reported to invade Xinjiang of China in 1993 and it was effectively controlled in Mori County.  Since 2013, CPB has also been found in Jilin and Heilongjiang in Northeast China, and it likely migrated to these provinces from Russia.  Thus, China has become the frontier for the global CPB spread, and risk management and monitoring systems for this pest are urgently needed.  Here, we summarize pest management methods that are used in areas at the frontier of the CPB invasion, and put forward frameworks for further preventing and controlling of the spread of CPB.  The management methods for CPB can also serve as an example for the control of invasive species mitigation in frontier areas. 
     
    Section 3 The interaction between potato aphids and virus
    Aphids and their transmitted potato viruses: A continuous challenges in potato crops
    XU Yi, Stewart M. GRAY
    2020, 19(2): 367-389.  DOI: 10.1016/S2095-3119(19)62842-X
    Abstract ( )   PDF in ScienceDirect  
    Aphid is one of the most destructive insect pests on cultivated plants in temperate regions.  Their piercing-sucking mouthparts and phloem feeding behavior directly damage crops and deplete plant nutrients.  Potato (Solanum tuberosum L.) is one of the most important food sources on the planet, and several aphid species, e.g., Myzus persicae (Sulzer) (green peach aphid) and Macrosiphum euphorbiae (Thomas) (potato aphid) (Hemiptera: Aphididae) colonize potato and transmit several economically important viruses.  Aphid-transmitted potato viruses have been emerging all over the world as a very serious problem in potato production, inducing a wide variety of foliar and tuber symptoms, leading to severe yield reduction and loss of tuber quality.  In this review, recent advances in understanding the interactions of potato viruses with their hosts, aphid vectors and the environment are described. 
     
    Simulation modelling of potato virus Y spread in relation to initial inoculum and vector activity
    Andrew GALIMBERTI, Andrei ALYOKHIN, Hongchun QU, Jason ROSE
    2020, 19(2): 376-388.  DOI: 10.1016/S2095-3119(19)62656-0
    Abstract ( )   PDF in ScienceDirect  
    Potato virus Y (PVY) is a non-persistent virus that is transmitted by many aphid species and causes significant damage to potato production.  We constructed a spatially-explicit model simulating PVY spread in a potato field and used it to investigate possible effects of transmission efficiency, initial inoculum levels, vector behavior, vector abundance, and timing of peak vector activity on PVY incidence at the end of a simulated growing season.  Lower PVY incidence in planted seed resulted in lower virus infection at the end of the season.  However, when populations of efficient PVY vectors were high, significant PVY spread occurred even when initial virus inoculum was low.  Non-colonizing aphids were more important for PVY spread compared to colonizing aphids, particularly at high densities.  An early-season peak in the numbers of non-colonizing aphids resulted in the highest number of infected plants in the end of the season, while mid- and late-season peaks caused relatively little virus spread.  Our results highlight the importance of integrating different techniques to prevent the number of PVY-infected plants from exceeding economically acceptable levels instead of trying to control aphids within potato fields.  Such management plans should be implemented very early in a growing season.
    Section 4 Integrative management strategies for potato insect pests
    Potential of Steinernema carpocapsae (Weiser) as a biological control agent against potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)
    YAN Jun-jie, Shovon Chandra SARKAR, MENG Rui-xia, Stuart REITZ, GAO Yu-lin
    2020, 19(2): 389-393.  DOI: 10.1016/S2095-3119(19)62826-1
    Abstract ( )   PDF in ScienceDirect  
    The entomopathogenic nematode, Steinernema carpocapsae, was evaluated for control of the potato tuber moth, Phthorimaea operculella, under laboratory conditions.  We evaluated different concentrations of S. carpocapsae for control of 2nd, 3rd, and 4th instar P. operculella.  The median lethal concentration (LC50) of S. carpocapsae infective juveniles (IJs) to 2nd, 3rd and 4th instar larvae of P. operculella was 200, 363, 181 IJs mL–1, respectively.  With the extension of treatment time, the cumulative mortality increased for 2nd, 3rd, and 4th instar larvae and pupae of P. operculella.  Fourth instars were the most susceptible for all observation periods.  Therefore, our results suggest that S. carpocapsae could be an effective biological control agent for P. operculella.
     
    Potato/Maize intercropping reduces infestation of potato tuber moth, Phthorimaea operculella (Zeller) by the enhancement of natural enemies
    ZHENG Ya-qiang, ZHANG Li-min, CHEN Bin, YAN Nai-sheng, GUI Fu-rong, ZAN Qing-an, DU Guang-zu, HE Shu-qi, LI Zheng-yue, GAO Yu-lin, XIAO Guan-li
    2020, 19(2): 394-405.  DOI: 10.1016/S2095-3119(19)62699-7
    Abstract ( )   PDF in ScienceDirect  
    The potato tuber moth (PTM), Phthorimaea operculella (Zeller), is one of the most economically significant insect pests for potato in both field and storage worldwide.  To evaluate the infestation, reduction of potato yield and the control efficacy for PTM, field tests were conducted in two seasons by intercropping of potato as the host plant with maize as a non-host plant of PTM.  Three intercropping patterns were tested, which were 2 rows of potatoes with either 2, 3, or 4 rows of maize (abbreviated 2P:2M, 2P:3M, and 2P:4M), and the monocropped potato as the control, 2 rows of potatoes, without maize,  (abbreviated 2P:0M).  Results showed that the population and infestation of PTM in the 2P:3M intercropping pattern was significantly lower than those in 2P:2M, 2P:4M and the monocropping pattern of 2P:0M, due to the enhancement of natural enemies.  Cumulative mines and tunneling in potato leaves in 2P:3M intercropping were significantly lower than those in 2P:2M and 2P:4M patterns.  The population of parasitoids and the parasitism rate of PTM in intercropping pattern of 2P:3M were significantly higher than that in intercropping pattern of 2P:2M, 2P:4M and monocropping pattern of 2P:0M.  We conclude that the potato intercropped with maize reduced the adult and larva populations, and reduced the damage from PTM by enhancing the number of parasitoids and the level of parasitism.  The greatest population density of parasitoids and parasitism rate were in the intercropping pattern of 2 rows of potatoes with 3 rows of maize.  These data indicate that the host/non-host intercropping patterns can be used as a biological control tactic against PTM by enhancing the density of natural enemies in the agro-ecosystems.
     
    Botanicals and plant strengtheners for potato and tomato cultivation in Africa
    Tewodros MULUGETA, Jean-Baptiste MUHINYUZA, Reinette GOUWS-MEYER, Lerato MATSAUNYANE, Erik ANDREASSON, Erik ALEXANDERSSON
    2020, 19(2): 406-427.  DOI: 10.1016/S2095-3119(19)62703-6
    Abstract ( )   PDF in ScienceDirect  
    This review provides a summary of botanicals and plant strengtheners that have potential uses for disease and pest management in potato and tomato cultivation in African.  We discuss their possible use to prevent major diseases and pests which infest potato and tomato, such as early and late blight, bacterial wilt, potato tuber moth, and tomato leafminer.  There are several examples of the successful uses of botanicals for pathogen and pest control relevant for different African climatic conditions; however, most of these studies have been conducted in vitro and often lack field verification.  Plant strengtheners (substances that induce and improve crop resistance, yield, and quality) are little studied and used in Africa in comparison to North America and Europe.  The possible benefits of using botanicals and plant strengtheners instead of conventional pesticides are discussed here in relation to human health and the environment as well as their modes of action and accessibility to farmers.  Lack of knowledge of the composition and active ingredients of extracts, environmental concerns, uncertainties regarding stability and formulation, lack of legislation and limited support from governments, hamper the development of botanicals and plant strengtheners for use in sustainable African agriculture.
    RNA interference in Colorado potato beetle (Leptinotarsa decemlineata): A potential strategy for pest control
    MA Mei-qi, HE Wan-wan, XU Shi-jing, XU Le-tian, ZHANG Jiang
    2020, 19(2): 428-427.  DOI: 10.1016/S2095-3119(19)62702-4
    Abstract ( )   PDF in ScienceDirect  
    Colorado potato beetle (CPB), Leptinotarsa decemlineata, is a notorious destructive pest that mainly feeds on the leaves of potato and several other solanaceous plants.  CPB is widely recognized for its adaptation to a remarkable variety of host plants and diverse climates, and its high resistance to insecticides and Bacillus thuringiensis toxins.  RNA interference (RNAi) is a sequence-specific, endogenous gene silencing mechanism evoked by small RNA molecules that is used as a robust tool for virus and pest control.  RNAi has been extensively tested for CPB management by employing various target genes and delivery methods.  This article reviews the screening of RNAi target genes, efficient RNAi delivery systems, and factors affecting RNAi efficiency in CPB, which may help understand the mechanisms of RNAi and its application in CPB control strategy.
     
    Crop Science
    Genetic progress in stem lodging resistance of the dominant wheat cultivars adapted to Yellow-Huai River Valleys Winter Wheat Zone in China since 1964
    ZHANG Hong-jun, LI Teng, LIU Hong-wei, MAI Chun-yan, YU Guang-jun, LI Hui-li, YU Li-qiang, MENG Ling-zhi, JIAN Da-wei, YANG Li, LI Hong-jie, ZHOU Yang
    2020, 19(2): 438-448.  DOI: 10.1016/S2095-3119(19)62627-4
    Abstract ( )  
    Analysis of genetic progress for lodging-related traits provides important information for further improvement of lodging resistance.  Forty winter wheat cultivars widely grown in the Yellow-Huai River Valleys Winter Wheat Zone (YHWZ) of China during the period of 1964–2015 were evaluated for several lodging-related traits in three cropping seasons.  Plant height, height at center of gravity, length of the basal second internode, and lodging index decreased significantly in this period, and the average annual genetic gains for these traits were –0.50 cm or –0.62%, –0.27 cm or –0.60%, –0.06 cm or –0.63%, and –0.01 or –0.94%, respectively.  Different from other traits, stem strength showed a significant increasing trend with the breeding period, and the annual genetic gains were 0.03 N or 0.05%.  Correlation analysis showed that lodging index was positively correlated with plant height, height at center of gravity, and length of the basal second internode, but negatively correlated with stem strength.  Meanwhile, significantly positive correlations were observed between plant height, height at center of gravity, and length of the basal first and second internodes.  By comparison with the wild types, dwarfing genes had significant effects on all lodging-related traits studied except for length of the basal first internode and stem strength.  Principle component analysis demonstrated that plant height and stem strength were the most important factors influencing lodging resistance.  Clustering analysis based on the first two principle components further indicated the targets of wheat lodging-resistant breeding have changed from reducing plant height to strengthening stem strength over the breeding periods.  This study indicates that the increase of stem strength is vital to improve lodging resistance in this region under the high-yielding condition when plant height is in an optimal range.
     
    Genome-wide identification and comparative analysis of drought related genes in roots of two maize inbred lines with contrasting drought tolerance by RNA sequencing
    HAO Lu-yang, LIU Xu-yang, ZHANG Xiao-jing, SUN Bao-cheng, LIU Cheng, ZHANG Deng-feng, TANG Huai-jun, LI Chun-hui, LI Yong-xiang, SHI Yun-su, XIE Xiao-qing, SONG Yan-chun, WANG Tian-yu, LI Yu
    2020, 19(2): 449-464.  DOI: 10.1016/S2095-3119(19)62660-2
    Abstract ( )   PDF in ScienceDirect  
    Drought is one of the most important abiotic stresses affecting maize growth and development and therefore resulting in yield loss.  Thus it is essential to understand molecular mechanisms of drought stress responses in maize for drought tolerance improvement.  The root plays a critical role in plants sensing water deficit.  In the present study, two maize inbred lines, H082183, a drought-tolerant line, and Lv28, a drought-sensitive line, were grown in the field and treated with different water conditions (moderate drought, severe drought, and well-watered conditions) during vegetative stage.  The transcriptomes of their roots were investigated by RNA sequencing.  There were 1 428 and 512 drought-responsive genes (DRGs) in Lv28, 688 and 3 363 DRGs in H082183 under moderate drought and severe drought, respectively.  A total of 31 Gene Ontology (GO) terms were significantly over-represented in the two lines, 13 of which were enriched only in the DRGs of H082183.  Based on results of Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis, “plant hormone signal transduction” and “starch and sucrose metabolism” were enriched in both of the two lines, while “phenylpropanoid biosynthesis” was only enriched in H082183.  Further analysis revealed the different expression patterns of genes related to abscisic acid (ABA) signal pathway, trehalose biosynthesis, reactive oxygen scavenging, and transcription factors might contribute to drought tolerance in maize.  Our results contribute to illustrating drought-responsive molecular mechanisms and providing gene resources for maize drought improvement.
    Exogenous strigolactones promote lateral root growth by reducing the endogenous auxin level in rapeseed
    MA Ni, WAN Lin, ZHAO Wei, LIU Hong-fang, LI Jun, ZHANG Chun-lei
    2020, 19(2): 465-482.  DOI: 10.1016/S2095-3119(19)62810-8
    Abstract ( )   PDF in ScienceDirect  
    Strigolactones (SLs) are newly discovered plant hormones which regulate the normal development of different plant organs, especially root architecture.  Lateral root formation of rapeseed seedlings before winter has great effects on the plant growth and seed yield.  Here, we treated the seedlings of Zhongshuang 11 (ZS11), an elite conventional rapeseed cultivar, with different concentrations of GR24 (a synthetic analogue of strigolactones), and found that a low concentration (0.18 µmol L–1) of GR24 could significantly increase the lateral root growth, shoot growth, and root/shoot ratio of seedlings.  RNA-Seq analysis of lateral roots at 12 h, 1 d, 4 d, and 7 d after GR24 treatment showed that 2 301, 4 626, 1 595, and 783 genes were significantly differentially expressed, respectively.  Function enrichment analysis revealed that the plant hormone transduction pathway, tryptophan metabolism, and the phenylpropanoid biosynthesis pathway were over-represented.  Moreover, transcription factors, including AP2/ERF, AUX/IAA, NAC, MYB, and WRKY, were up-regulated at 1 d after GR24 treatment.  Metabolomics profiling further demonstrated that the amounts of various metabolites, such as indole-3-acetic acid (IAA) and cis-zeatin were drastically altered.  In particular, the concentrations of endogenous IAA significantly decreased by 52.4 and 75.8% at 12 h and 1 d after GR24 treatment, respectively.  Our study indicated that low concentrations of exogenous SLs could promote the lateral root growth of rapeseed through interaction with other phytohormones, which provides useful clues for the effects of SLs on root architecture and crop productivity.
     
    Higher leaf area through leaf width and lower leaf angle were the primary morphological traits for yield advantage of japonica/indica hybrids
    WEI Huan-he, YANG Yu-lin, SHAO Xing-yu, SHI Tian-yi, MENG Tian-yao, LU Yu, TAO Yuan, LI Xin-yue, DING En-hao, CHEN Ying-long, DAI Qi-gen
    2020, 19(2): 483-494.  DOI: 10.1016/S2095-3119(19)62628-6
    Abstract ( )   PDF in ScienceDirect  
    The yield potential of japonica/indica hybrids (JIH) has been achieved over 13.5 t ha–1 in large-scale rice fields, and some physiological traits for yield advantage of JIH over japonica inbred rice (JI) and indica hybrid rice (IH) were also identified.  To date, little attention has been paid to morphological traits for yield advantage of JIH over JI and IH.  For this reason, three JIH, three JI, and three IH were field-grown at East China (Ningbo, Zhejiang Province) in 2015 and 2016.  Compared with JI and IH, JIH had 14.3 and 20.8% higher grain yield, respectively, attributed to its more spikelets per panicle and relatively high percentage of filled grains.  The advantage in spikelets per panicle of JIH over JI and IH was shown in number of grains on the upper, middle, and lower branches.  Compared with JI and IH, JIH had higher leaf area through leaf width and lower leaf angle of upper three leaves, higher leaf area index and leaf area per tiller at heading and maturity stages, higher stem weight per tiller and K and Si concentrations of stem at maturity, higher dry matter weight in leaf, stem, and panicle at heading and maturity stages, and higher biomass accumulation after heading and lower biomass translocation from stem during ripening.  Leaf width of upper three leaves were correlated positively, while leaf angle of upper three leaves were correlated negatively with biomass accumulation after heading, stem weight per tiller, and per unit length.  Our results indicated that the grain yield advantage of JIH was ascribed mainly to the more spikelets per panicle and relatively high percentage of filled grains.  Higher leaf area through leaf width and more erect leaves were associated with improved biomass accumulation and stem weighing during ripening, and were the primary morphological traits underlying higher grain yield of JIH.
     
    Screening of drought resistance indices and evaluation of drought resistance in cotton (Gossypium hirsutum L.)
    ZOU Jie, HU Wei, LI Yu-xia, HE Jia-qi, ZHU Hong-hai, ZHOU Zhi-guo
    2020, 19(2): 495-508.  DOI: 10.1016/S2095-3119(19)62696-1
    Abstract ( )   PDF in ScienceDirect  
    Sixteen cotton cultivars widely planted in China were sowed under five different drought concentrations (0, 2.5, 5, 7.5, and 10%) using PEG6000 to screen the indices of drought resistance identification and explore the drought resistance of different cotton cultivars.  Eighteen physiological indices including root, stem, and leaf water contents (RWC, SWC, and LWC), net photosynthetic rate (Pn), the maximum photochemical quantum yield (Fv/Fm), the actual photochemical quantum yield (ΦPSII), non-photochemical quenching coefficient (NPQ), leaf water potential (LWP), osmotic potential (Ψs), leaf relative conductivity (REC), leaf proline content (Pro), leaf and root soluble protein contents (LSPC and RSPC), leaf and root malondialdehyde (MDA) contents (LMDA and RMDA), root superoxide dismutase, peroxidase, and catalase activities (RSOD, RPOD, and RCAT) were measured.  Results indicated the 18 physiological indices can be converted into five or six independent comprehensive indices by principal component analysis, and nine typical indices (Fv/Fm, SWC, LWP, Pro, LMDA, RSPC, RMDA, RSOD, and RCAT) screened out by a stepwise regression method could be utilized to evaluate the drought resistance.  Moreover, the 16 cotton cultivars were divided into four types: drought sensitive, drought weak sensitive, moderate drought resistant, and drought resistant types.  The resistance ability of two selected cotton cultivars (drought resistant cultivar, Dexiamian 1; drought sensitive cultivar, Yuzaomian 9110) with contrasting drought sensitivities were further verified by pot experiment.  Results showed that the responses of final cotton biomass, yield, and yield composition to drought were significantly different between the two cultivars.  In conclusion, drought resistant cultivar Dexiamian 1 and drought sensitive cultivar Yuzaomian 9110 were screened through hydroponics experiment, which can be used as ideal experimental materials to study the mechanism of different cotton cultivars with contrasting drought sensitivities in response to drought stress.
     
    One-time fertilization at first flowering improves lint yield and dry matter partitioning in late planted short-season cotton
    LUO Hong-hai, WANG Qiang, ZHANG Jie-kun, WANG Lei-shan, LI Ya-bing, YANG Guo-zheng
    2020, 19(2): 509-517.  DOI: 10.1016/S2095-3119(19)62623-7
    Abstract ( )   PDF in ScienceDirect  
    Cotton producers have substantially reduced their inputs (labor, nutrients, and management) mainly by adopting a short-season cropping management that is characterized by late sowing, high density, and reduced fertilization with one-time application at the first bloom stage without lint yield reduction.  However, it has been hypothesized that one-time fertilization at an earlier growth stage could be a more effective and economic management practice.  A two-year field experiment was conducted by applying five fertilizer one-time fertilization at 0 (FT1), 5 (FT2), 10 (FT3), 15 (FT4), and 20 (FT5) days after the first flower appeared in the field and one three-split fertilizer application taken as the conventional control (FT6), making six treatments altogether.  Cotton growth period, biomass accumulation, yield, and its formation were quantified.  The results showed that the one-time fertilization did not affect the cotton growth progress as compared to FT6, however, the total crop cycles for FT3–FT5 were 3 days shorter.  FT1 produced the highest cotton lint yield (1 396 kg ha–1), which was similar to the FT6 but higher than the other treatments, and could be attributed to more bolls per unit area and higher lint percentage. Cotton yield was positively correlated with cotton plant biomass accumulated.  FT1 had both the highest average (VT) (193.7 kg ha–1 d–1) and the highest maximum (VM) (220.9 kg ha–1 d–1) rates during the fast biomass accumulation period.  These results suggest that one-time fertilizer application at the first flower stage might be an adjustment that is more effective than at first bloom, and allowed for easier decision making for application date due to non counting of plants with flowers is needed.
     
    Horticulture
    Allelochemical p-hydroxybenzoic acid inhibits root growth via regulating ROS accumulation in cucumber (Cucumis sativus L.)
    HUANG Cheng-zhen, XU Lei, Sun Jin-jing, ZHANG Zhong-hua, FU Mei-lan, TENG Hui-ying, YI Ke-ke
    2020, 19(2): 518-527.  DOI: 10.1016/S2095-3119(19)62781-4
    Abstract ( )   PDF in ScienceDirect  
    Allelopathy is prevalent in agricultural ecosystems and mediated by plant-derived secondary metabolites (allelochemicals).  Allelochemicals are released by donor plants and affect the root growth and development of receptor plants.  Allelopathy is responsible for the continuous cropping obstacles in cucumber (Cucumis sativus L.).  p-Hydroxybenzoic acid (pHBA), an autotoxin from root exudates of cucumber, has been proposed to be an important allelopathic chemical.  However, the molecular mechanism by which pHBA affect root growth and development in cucumber is unknown.  Here, we found that pHBA treatment suppressed root growth of cucumber by reducing the meristem activity and cell length.  This root growth defect is caused by reduced reactive oxygen species (ROS) accumulation in root tips.  After pHBA treatment, the expression levels of several ROS-scavenging-related genes were increased, including peroxidase (POD), catalase (CAT) and metallothionein (MT).  Moreover, exogenously application of salicylhydroxamate (SHAM), a peroxidase inhibitor, can partially restore the pHBA treatment induced root growth inhibition.  Furthermore, we found that there is natural variation for the inhibitory effect of pHBA on root growth.  We also showed that pHBA treatment could maintain higher level of ROS accumulated in the pHBA less sensitive cucumber than that in the pHBA-sensitive cucumber.  These results suggest that pHBA inhibits root growth by reducing root tip ROS level in cucumber.
     
    Comparative transcriptome analysis of the effect of different heat shock periods on the unfertilized ovule in watermelon (Citrullus lanatus)
    ZHU Ying-chun, SUN De-xi, DENG Yun, AN Guo-lin, LI Wei-hua, SI Wen-jing, LIU Jun-pu, SUN Xiao-wu
    2020, 19(2): 528-540.  DOI: 10.1016/S2095-3119(19)62777-2
    Abstract ( )   PDF in ScienceDirect  

    In vitro gynogenesis is an important tool used in haploid or homozygous double-haploid plant breeding.  However, because of low repeatability, embryoid induction rate and quality, the molecular mechanisms remain poorly understood.  Heat shock treatment can promote the transformation of the gametophytic pathway into the sporophyte pathway, which induces the occurrence of haploid.  In this study, unfertilized ovaries were heat shocked for 0 h (A0) before flowering and for 0 h (A1), 4 h (A3), 8 h (A5), 12 h (A7), and 24 h (A8), respectively, at 37°C at the first day of the flowering stage.  The ovule enlargement rate was increased from 0% at 25°C to 96.8% at 37°C (24 h treatment).  Thus, we aimed to investigate the gene expression patterns in unfertilized ovules of watermelon after different periods of heat shock by using RNA-Seq technology.  The results showed that compared with A3, A5, A7, and A8, the biosynthesis of amino acid, glycine, serine and threonine metabolic pathways in A1 has changed significantly.  This indicated that heat shock treatment affected the synthesis and transformation of amino acids during ovule expansion.  The transcriptome data suggested gene expressions of ovule growth were significantly changed by heat-specific influences.  The results provide new information on the complex relationship between in vitro gynogenesis and temperature.  This provides a basis for further study of the mechanism of heat shock affecting the expansion of watermelon ovule. 

    Plant Protection
    Bioinformatic analysis and functional characterization of the cfem proteins in maize anthracnose fungus Colletotrichum graminicola
    GONG An-dong, JING Zhong-ying, ZHANG Kai, TAN Qing-qun, WANG Guo-liang, LIU Wen-de
    2020, 19(2): 541-550.  DOI: 10.1016/S2095-3119(19)62675-4
    Abstract ( )   PDF in ScienceDirect  
    Fungal secreted proteins that contain the Common in Fungal Extracellular Membrane (CFEM) domain are important for pathogenicity.  The hemibiotrophic fungus Colletotrichum graminicola causes the serious anthracnose disease of maize.  In this study, we identified 24 CgCFEM proteins in the genome of C. graminicola.  Phylogenic analysis revealed that these 24 proteins (CgCFEM1–24) can be divided into 2 clades based on the presence of the trans-membrane domain.  Sequence alignment analysis indicated that the amino acids of the CFEM domain are highly conserved and contain 8 spaced cysteines, with the exception that CgCFEM1 and CgCFEM24 lack 1 and 2 cysteines, respectively.  Ten CgCFEM proteins with a signal peptide and without the trans-membrane domain were considered as candidate effectors and, thus were selected for structural prediction and functional analyses.  The CFEM domain in the candidate effectors can form a helical-basket structure homologous to the Csa2 protein in Candida albicans, which is responsible for haem acquisition and pathogenicity.  Subcellular localization analysis revealed that these effectors accumulate in the cell membrane, nucleus, and cytosolic bodies.  Additionally, 5 effectors, CgCFEM6, 7, 8, 9 and 15, can suppress the BAX-induced programmed cell death in Nicotiana benthamiana with or without the signal peptide.  These results demonstrate that these 10 CgCFEM candidate effectors with different structures and subcellular localizations in host cells may play important roles during the pathogenic processes on maize plants.
     
    A new Curvularia lunata variety discovered in Huanghuaihai Region in China
    CHANG Jia-ying, LIU Shu-sen, SHI Jie, GUO Ning, ZHANG Hai-jian, CHEN Jie
    2020, 19(2): 551-560.  DOI: 10.1016/S2095-3119(19)62655-9
    Abstract ( )   PDF in ScienceDirect  
    The purpose of this study was to identify the dominant pathogens of Curvularia leaf spot and their pathogenicity variation in Huanghuaihai Region of China in recent years.  In 2013 and 2016–2017, the occurrences of Curvularia leaf spots on maize were investigated in fields located in Henan, Hebei, Shandong, and Anhui provinces, and 292 fungi were isolated from diseased leaves.  These fungal isolates were subjected to morphological identification, and 232 isolates were found to have about 70% uncurved conidia and were identified as Curvularia lunata var.  Most of the conidia of 2 representative isolates, namely, HNWB-131 and HNWB-185, were oblong with parallel septations and were distinctly different from a reference isolate CX-3.  For further determination, the internal transcribed spacer (ITS), glyceraldehyde 3-phosphate dehydrogenase (GPDH), the large subunit (LSU), and translation elongation factor 1-alpha (EF1-α) sequences of HNWB-131, HNWB-185, and CX-3 were amplified and sequenced.  The results of sequence analysis showed that the 4 gene sequences from the 3 isolates had a similarity of more than 99% to C. lunata.  Based on the sequences of ITS and the combined data of the 4 genes, neighbor-joining trees were constructed for phylogenetic analysis.  The results indicated that these 3 isolates were clustered together with C. lunata. The expression of Clg2p and ClUrase genes in mycelia and conidia was significantly (P<0.05) higher in CX-3 than in HNWB-131 and HNWB-185.  This study found that the dominant pathogen of Curvularia leaf spot was a new variety of C. lunata with morphological variations in Huanghuaihai Region from 2013 to 2017.  The pathogenicity of the C. lunata var. was not significantly enhanced, and the expression of Clg2p and ClUrase genes of C. lunata var. was decreased.
    Application of droplet digital PCR in detection of seed-transmitted pathogen Acidovorax citrulli
    LU Yu, ZHANG Hai-jun, ZHAO Zi-jing, WEN Chang-long, WU Ping, SONG Shun-hua, YU Shuan-cang, Luo Lai-xin, XU Xiu-lan
    2020, 19(2): 561-569.  DOI: 10.1016/S2095-3119(19)62673-0
    Abstract ( )   PDF in ScienceDirect  
    Bacterial fruit blotch caused by Acidovorax citrulli is a serious threat to cucurbit industry worldwide.  The pathogen is seed-transmitted, so seed detection to prevent distribution of contaminated seed is crucial in disease management.  In this study, we adapted a quantitative real-time PCR (qPCR) assay to droplet digital PCR (ddPCR) format for A. citrulli detection by optimizing reaction conditions.  The performance of ddPCR in detecting A. citrulli pure culture, DNA, infested watermelon/melon seed and commercial seed samples were compared with multiplex PCR, qPCR, and dilution plating method.  The lowest concentrations detected (LCD) by ddPCR reached up to 2 fg DNA, and 102 CFU mL–1 bacterial cells, which were ten times more sensitive than those of the qPCR.  When testing artificially infested watermelon and melon seed, 0.1% infestation level was detectable using ddPCR and dilution plating method.  The 26 positive samples were identified in 201 commercial seed samples through ddPCR, which was the highest positive number among all the methods.  High detection sensitivity achieved by ddPCR demonstrated a promising technique for improving seed-transmitted pathogen detection threshold in the future.
     
    Molecular and biological characterization of melon-infecting squash leaf curl China virus in China 
    WU Hui-jie, LI Meng, HONG Ni, PENG Bin, GU Qin-sheng
    2020, 19(2): 570-577.  DOI: 10.1016/S2095-3119(19)62642-0
    Abstract ( )   PDF in ScienceDirect  
    It has been reported that squash leaf curl China virus (SLCCNV) infects some Cucurbitaceae crops except for melon (Cucumis melo L.).  A new disease of melon exhibiting severe leaf curl and dwarfing was observed in Hainan Province of China.  In this study, the pathogen was identified as SLCCNV through biological and molecular characterization.  The isolate (SLCCNV-HN) possess a bipartite genome, DNA-A (HM566112.1) with the highest nucleotide identity (99%) to SLCCNV-Hn (MF062251.1) pumpkin and SLCCNV-Hn61 (AM260205.1) squash isolates from China, whereas DNA-B (HM566113.1) with the highest nucleotide identity (99%) to SLCCNV-Hn (MF062252.1).  Phylogenetic analyses based on the full-length SLCCNV-HN DNA-A and -B sequences indicated that SLCCNV-HN melon isolate is clustered with SLCCNV-Hn pumpkin, SLCCNV-Hn61 and SLCCNV-SY squash isolates from southern China, forming an independent cluster.  Infectious clone of SLCCNV-HN was constructed and the melon plants were inoculated and the infection rate is 100%, the systemic symptoms in melon showed identical to those of melon plants infected in fields.  Additionally, melon plants transmission of this virus by Bemisia tabaci with a transmission rate of 95% (19/20) showed leaf curl and dwarf symptoms 15 days post transmission, thereby fulfilling Koch’s postulates.  Analysis of genomic organization and phylogenetic trees indicated that SLCCNV-HN melon isolate belongs to the Begomovirus genus.  To the best of our knowledge, this is the first characterization of melon-infecting SLCCNV through its genome, infectious clone and transmission.
     
    Agricultural Economics and Management
    Influence of surface ozone on crop yield of maize in China
    YI Fu-jin, FENG Jia-ao, WANG Yan-jun, JIANG Fei
    2020, 19(2): 578-589.  DOI: 10.1016/S2095-3119(19)62822-4
    Abstract ( )   PDF in ScienceDirect  
    This study investigated the adverse effect of surface ozone on the maize yield using a unique panel from 880 counties in China.  To identify the impact of elevated surface ozone concentrations, we constructed an econometric model by controlling the impact of climate variables and related economic variables.  This study also considered the potential spatial correlation in the measurement of the impact of surface ozone on maize yield.  Results confirmed that the increase of ozone concentration decreased the maize yield.  Moreover, maize was found to be the most sensitive to ozone at the end of the second month of the growing season.  The average annual loss of maize caused by ozone pollution is about 4.234 million tons in 2013–2015, accounting for 1.9% of the average output.
     
    Do large-scale farmers use more pesticides?  Empirical evidence from rice farmers in five Chinese provinces 
    QIN Shi-le, Lü Xin-ye
    2020, 19(2): 590-599.  DOI: 10.1016/S2095-3119(19)62864-9
    Abstract ( )   PDF in ScienceDirect  
    It is of great theoretical and practical significance to understand the rules of the differences in pesticide use behaviors between large-scale and small-scale farmers, so as to regulate the behavior of farmers differently and improve the quality and safety of rice.  The overall pesticide use behavior of large-scale farmers was characterized by large doses and high application frequency, while that of small-scale farmers was characterized by small doses and low application frequency.  The econometric test showed that (i) the proportion of staple food ration has a significant negative impact on the single dose exceeding the standard and pesticide application frequency of small-scale farmers, and the increase of the proportion of staple food ration will reduce the demand among small-scale farmers for pesticides; (ii) yield effect has a greater impact on the frequency of pesticide application by large-scale farmers, and the large yield effect will increase the frequency of pesticide application among large-scale farmers.  Therefore, in pesticide use behaviors, large-scale farmers should reduce pesticide quantity and increase efficiency, while small-scale farmers improve the level of plant protection.