• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Resistance to Aspergillus flavus in maize and peanut: Molecular biology,breeding,environmental stress, and future perspectives

    2015-11-24 12:23:57JkFountinPwnKhrLiminYnSpurthiNykBrinScullyRortZhiYunChnRortKmritRjvVrshnyBozhuGuo
    The Crop Journal 2015年3期

    Jk C.Fountin,Pwn Khr,,Limin Yn,d,Spurthi N.Nyk,Brin T.Scully, Rort D.L,Zhi-Yun Chn,Rort C.Kmrit,Rjv K.Vrshny,Bozhu Guo*

    aDepartment of Plant Pathology,University of Georgia,Tifton,GA,USA

    bInternational Crops Research Institute for the Semi-Arid Tropics(ICRISAT),Hyderabad,Telangana,India

    cUSDA-ARS,Crop Protection and Management Research Unit,Tifton,GA,USA

    dHuaiyin Normal University,School of Life Sciences,Huai'an,Jiangsu,China

    eUSDA-ARS,US Horticultural Laboratory,Fort Pierce,FL,USA

    fDepartment of Crop and Soil Sciences,University of Georgia,Tifton,GA,USA

    gDepartment of Plant Pathology and Crop Physiology,Louisiana State University,Baton Rouge,LA,USA

    Resistance to Aspergillus flavus in maize and peanut: Molecular biology,breeding,environmental stress, and future perspectives

    Jake C.Fountaina,Pawan Kheraa,b,c,Liming Yanga,c,d,Spurthi N.Nayakb,Brian T.Scullye, Robert D.Leef,Zhi-Yuan Cheng,Robert C.Kemeraita,Rajeev K.Varshneyb,Baozhu Guoc,*

    aDepartment of Plant Pathology,University of Georgia,Tifton,GA,USA

    bInternational Crops Research Institute for the Semi-Arid Tropics(ICRISAT),Hyderabad,Telangana,India

    cUSDA-ARS,Crop Protection and Management Research Unit,Tifton,GA,USA

    dHuaiyin Normal University,School of Life Sciences,Huai'an,Jiangsu,China

    eUSDA-ARS,US Horticultural Laboratory,Fort Pierce,FL,USA

    fDepartment of Crop and Soil Sciences,University of Georgia,Tifton,GA,USA

    gDepartment of Plant Pathology and Crop Physiology,Louisiana State University,Baton Rouge,LA,USA

    A R T I C L E I N F O

    Article history:

    Received 8 October 2014

    Received in revised form

    29 January 2015

    Accepted 2 February 2015

    Available online 11 April 2015

    Host resistance

    Molecular breeding

    Aflatoxin contamination

    Reactive oxygen species

    ROS

    The colonization of maize(Zea mays L.)and peanut(Arachis hypogaea L.)by the fungal pathogen Aspergillus flavus results in the contamination of kernels with carcinogenic mycotoxins known as aflatoxins leading to economic losses and potential health threats to humans.The regulation of aflatoxin biosynthesis in various Aspergillus spp.has been extensively studied,and has been shown to be related to oxidative stress responses.Given that environmental stresses such as drought and heat stress result in the accumulation of reactive oxygen species(ROS)within host plant tissues,host-derived ROS may play an important role in cross-kingdom communication between host plants and A.flavus.Recent technological advances in plant breeding have provided the tools necessary to study and apply knowledge derived from metabolomic,proteomic,and transcriptomic studies in the context of productive breeding populations.Here,we review the current understanding of the potential roles of environmental stress,ROS,and aflatoxin in the interaction between A.flavus and its host plants,and the current status in molecular breeding and marker discovery for resistance to A.flavus colonization and aflatoxin contamination in maize and peanut.We will also propose future directions and a working model for continuing research efforts linking environmental stress tolerance and aflatoxin contamination resistance in maize and peanut.

    ?2015 Crop Science Society of China and Institute of Crop Science,CAAS.Production and hosting by Elsevier B.V.All rights reserved.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

    1.Introduction

    The colonization of maize and peanut by Aspergillus flavus and Aspergillus parasiticus(Link ex Fr.and Speare,respectively; teleomorphs:Petromyces flavus and Petromyces parasiticus)[1,2] results in contamination of their derived agricultural products with aflatoxins[3].Aflatoxins are among the most potent mycotoxins,carcinogenic and teratogenic compounds,produced during infection and growth of fungi A.flavus and A. parasiticus on crops such as maize,peanut,cottonseed and tree nuts.Maize and peanuts are the most susceptible crops to aflatoxin contamination and serve as the main source of aflatoxin contamination for humans[4].Aflatoxins not only have been associated with numerous diseases and disorders in humans and livestock,but also have a negative economic impact due to loss of crop value[5–7].Resistance to A.flavus colonization and subsequent aflatoxin production is a complex phenomenon involving numerous genetic,physiological, and morphological factors and acts as a quantitative trait [8–10].

    Examination of the functional composition of resistance mechanisms in maize and,to a lesser extent,in peanut using transcriptomic,proteomic,and metabolomic approaches has led to the elucidation of the roles of several specific genes, proteins,and signal molecules including pathogenesis-related proteins(such as PR-10,PR-10.1,14-kDa trypsin inhibitor, chitinase,zeamatin,and B1,3-glucanase),stress-responsive proteins(such as catalase,superoxide dismutase,glyoxalase I, and glutathione-S-transferase),and reactive oxygen species (ROS)in regulating A.flavus resistance as well as their potential roles in cross-kingdom communication between host plants and Aspergillus spp.[11–20].In addition,the link that exists between aflatoxin contamination and environmental stress, particularly drought stress,has also been a focal point of molecular research and applied breeding programs in recent years[5,21–25].Hence,the use of drought tolerant germplasm with aflatoxin resistance has gained momentum for selection in various genetic studies[21,26].

    Despite considerable advances in molecular research,a complete understanding of the details of the host-parasite interaction between A.flavus and its hosts including maize and peanut,namely the precise signaling mechanisms employed in this interaction,remains elusive and there is a need for continuing investigation.Therefore,in this review we focus on recent findings related to the biochemistry of defense regulation with regard to environmental stress,ROS,and inter-cellular communication between A.flavus and its host crops.In addition,recent advances in conventional and molecular breeding for aflatoxin resistance in maize and peanut,and the potential utilization of molecular markers for use in marker assisted selection(MAS)in breeding programs are highlighted.

    2.Molecular biology of potential host-A.flavus interactions mediated by ROS

    The molecular and biochemical bases of the interaction between the host crops and A.flavus has been the subject of numerous studies in recent years for identifying both the sources of resistance to A.flavus colonization,and the regulation of aflatoxin biosynthesis in A.flavus and other Aspergilli including Aspergillus fumigatus and A.parasiticus. Integration of the findings of these studies into a coherent model for explaining the subtleties of the interaction is lacking in the literature.In addition,the functional roles ofthe components/genes thought to be involvedin the host-pathogen interactions were not well characterized.Hence,the potential components of the interaction and their implications for future research efforts are discussed.

    2.1.Pathogen recognition and upstream resistance gene expression regulation

    The plant-pathogen recognition is the first step in the interaction which causes rapid activation of appropriate defensive and infective mechanisms in the plant and the pathogen,respectively.Using maize as an example,the recognition of A.flavus by maize cells in contact with the pathogen and the subsequent transcriptional activation of the upstream defense signaling system constitute the first line of defense and response to infection.But the precise upstream recognition mechanisms employed by maize or peanut against A.flavus are not currently known. However,recent studies on WRKY transcription factors in maize[27]and model species such as Arabidopsis thaliana [28]may provide insight into this aspect of defense initiation.

    WRKY transcription factors,which possess a rarely variable amino acid sequence of“WRKY”at the amino terminus of their DNA binding domain,function in the upstream regulation of various cellular processes in plants and other organisms,including pathogen defense response coordination[28].It has been demonstrated that two WRKY transcription factor-encoding genes,ZmWRKY19 and ZmWRKY53,were significantly up-regulated by A.flavus inoculation in the resistant maize line TZAR101,and may play an important role in regulating upstream defense responses in developing maize kernels in response to A.flavus inoculation[27].The ortholog of ZmWRKY19 in Arabidopsis,AtWRKY53,in contrast, functions in oxidative stress responses by promoting the expression of catalase and other antioxidant genes,and has been shown to interact with calmodulins[29,30].ZmWRKY53 has been shown to enhance abiotic stress tolerance,including drought and salt stress[31].Similarly,the WRKY genes were found to be associated with conferring tolerance to salinity in interspecific derivatives of peanut[32].The ortholog of ZmWRKY53 in Arabidopsis,AtWRKY33,has also been demonstrated to function in necrotrophic pathogen defense responses and thermotolerance while its orthologs in wheat (TaWRKY53)and rice(OsWRKY53)were shown to function in regulating chitinase and peroxidase gene expression[33].

    Interestingly,the Arabidopsis orthologs of these WRKY transcription factorsare directlyregulated bymitogen activated protein kinase(MAPK)pathways,including MEKK1 and MPK3/6,in response to chitin perception by receptor kinases as a part of a pathogen associated molecular pattern (PAMP)-triggered immunity(PTI)mechanism[28,29,34–37]. This prospect of chitin perception as a trigger for PTI seemsplausible given that previous research demonstrated that resistant maize lines accumulate chitinase,which may provide a source for chitin monomers that can be perceived by receptor kinases[17].Also,given the high level of expression of these orthologous WRKY genes in resistant maize,it is possible that such a signal transduction and receptor system may be present in maize and functional in the maize–A.flavus interaction[27].In addition,appropriate studies need to be carried out in peanut to determine the role of WRKY genes in initiation of plant defense mechanisms. Furthermore,the expression of WRKY transcription factors in response to A.flavus inoculation might result in increased expression of antioxidant and pathogenesis-related genes in resistant maize lines providing enhanced oxidative stress tolerance and pathogen resistance(Fig.1-A)[5,27].

    2.2.Calcium signaling and reactive oxygen species(ROS)in defense regulation

    In addition to MAPK signaling to promote the expression of defense-related genes,calcium signaling and reactive oxygen species(ROS)play a role in regulating defense responses. Recently,Ma and Berkowitz[38]reviewed the Ca2+-calmodulin signaling and its role in regulating defense activation and hypersensitive cell death.Briefly,as a part of PTI responses, receptor kinase-bound nucleotidyl cyclases activate cyclic nucleotide gated ion channels(CNGCs)through cAMP or cGMP signal intermediates.This results in the influx of Ca2+ions into the plant cell cytosol and the activation of calmodulins and calcium dependent protein kinases(CDPKs).These CDPKs then, in turn,activate the transmembrane protein complex NADPHoxidase which converts molecular O2to a superoxide anion(O2?). The superoxide anion is then detoxified by superoxide dismutase(SOD)to form H2O2whose neutral charge allows it to pass through the plasma membrane and function in cytosolic defense signaling.In maize,Jiang and Zhang[39]demonstrated a similar mechanism functional in oxidative stress responses. Another study by Hu et al.[40]further demonstrated an interaction between Ca2+/calmodulin signaling components and abscisic acid(ABA)-based ROS defense responses.

    Fig.1-Hypothetical biochemical pathways and reactions present in the maize-A.flavus interaction.(A)The perception of chitin by receptor kinases activates a MAPK cascade leading to the expression of maize WRKY transcription factors ZmWRKY19 and 53 which promote the expression of antioxidant and pathogenesis-related gene expression;(B)PAMP triggered immunity(PTI)reactions lead to the activation of calcium signaling pathways resulting in the production of extracellular superoxide anions which are detoxified to hydrogen peroxide by superoxide dismutase(SOD);(C)Extracellular hydrogen peroxide functions in cross-kingdom communication between maize and A.flavus resulting in the stimulation of cAMP signaling and subsequent expression of genes encoding for stress response proteins and aflatoxin biosynthetic components;(D)The final stages of aflatoxin biosynthesis are confined to specialized structures known as aflatoxisomes while aflatoxin-derived and environmental ROS are detoxified by various stress response proteins.Host derived oxylipins may also stimulate conidiation and inhibit aflatoxin biosynthesis;(E)Aflatoxin is secreted from A.flavus and absorbed into the maize cell resulting in oxidative damage to DNA and other cellular components leading to cell death.Solid lines represent characterized pathways from the literature.Dashed lines represent hypothetical junctures between the components of the interaction.

    The presence of calcium/calmodulin signaling in maize is interesting because of the role of calmodulin in regulation of AtWRKY53,the ortholog of ZmWRKY19,in order to stimulate antioxidant gene expression[29,30].Also,free mobility of H2O2across cell membranes and its role as a source of oxidative stress,as H2O2as a mobile signaling molecule, involves in cross-kingdom communication between maize and A.flavus or other invading pathogens(Fig.1-B).The role of cytosolic levels of Ca2+ions in stimulating these responses may also be relevant to the interaction between maize resistance to A.flavus and drought stress since cytosolic levels of Ca2+would be proportionally higher due to water loss under drought stress conditions that activate the associated signaling mechanisms.However,detailed studies are needed to validate the role of Ca2+signaling in regulating resistance to A. flavus in maize and other crop species.

    2.3.Potential role of ROS in aflatoxin biosynthesis and stress responsive gene regulation

    As the defense signaling-derived ROS are generated extracellularly,they may stimulate the production of aflatoxin by Aspergillus spp.potentially as a part of an antioxidative defense mechanism[5].A recent study by Roze et al.[41] demonstrated that aflatoxin biosynthesis and stress response are potentially linked in A.parasiticus by a transcription factor complex with the basic leucine zipper(bZIP)transcription factors AtfB and AP-1,in response to available carbohydrate or oxidative stress through a cAMP signaling mechanism.The protein complex directly promotes the expression of genes pertaining to secondary metabolism,particularly in aflatoxin biosynthesis.This study postulates that the protein complex or its components stimulate the expression of antioxidant defense genes and the promoters of the antioxidant genes are bound by bZIP transcription factors(Fig.1-C).In addition,ROS cross-talk between the host plant cell and Aspergillus spp.may also result in the formation of oxylipins which regulate the reproductive development of Aspergilli as well as aflatoxin production[5,42–44](Fig.1-D,E).

    2.4.Aflatoxin metabolism and potential effects on plant cell physiology

    The connection between ROS-derived oxidative stress and aflatoxin production seems to indicate the antioxidant property of aflatoxin that may favor growth and function of A.flavus or other Aspergilli and would,therefore,be advantageous for fungal survivability.However,it is possible that the opposite is true,and this link may be useful to remediate oxidative stress caused by aflatoxin reacting with fungal cellular components. This seems plausible given two considerations.

    First,the final stages of aflatoxin biosynthesis are confined to specialized,membrane-bound organelles termed aflatoxisomes [45–48].This compartmentalization of aflatoxin biosynthesis followed by direct exocytosis lends itself to the possibility that mature aflatoxin compounds may be cytotoxic(Fig.1-D).However,further experimentation will be required in order to examine the precise aflatoxin detoxification and damage remediation mechanisms employed by Aspergillus spp.

    Second,aflatoxin may be metabolized by fungal or plant cells into toxic byproducts.Studies of the metabolism of aflatoxin B1(AFB1)by human hepatocytes revealed that cytochrome p450 monooxygenases are capable of oxidizing AFB1,resulting inthe bioactivation of thetoxin[49].Specifically, cytochrome p450-3A4 converts AFB1into an epoxidized form, AFB1-exo-8,9-epoxide,which readily reacts with DNAs tructures resulting in mutation and oxidative damage to various macromolecules[50].Conversely,cytochromep450-1A2convertsAFB1into AFB1-endo-8,9-epoxide which is non-reactive and rapidly detoxified[50].Since p450 monooxy genases are universally abundant in eukaryotic organisms,including maize[51],it is possible that aflatoxin is metabolized in a similar fashion in maize or peanut,resulting in oxidative damage to cellular components potentially leading to localized cell death(Fig.1-E). However,for such a reaction to occur,the ability of aflatoxin to be absorbed by plant cells and its subsequent metabolism remain fundamental issues to be addressed in future research endeavors.

    If indeed aflatoxin causes oxidative damage to cellular components of both pathogen and host,a question quickly arises.What is the advantage provided by the biosynthesis of aflatoxin?It was hypothesized in the literature that A.flavus functions as a facultative necrotroph during infection of maize kernel tissues[5,52].Aflatoxin could enhance pathogenicity by causing localized death of host cells surrounding the invading fungal mycelia,while A.flavus is afforded protection by the co-expression of high levels of stress responsive genes[41].In either case,detailed study of molecular mechanisms involved in aflatoxin biosynthesis in maize and peanut are needed to confirm these hypotheses.

    3.Breeding for aflatoxin resistance in maize: biomarkers,quantitative trait loci(QTL)discovery, and applications in conventional programs

    3.1.Biomarkers

    The preceding discussion on the biochemistry of the interaction between maize and A.flavus presents both challenges and opportunities for continuing research,particularly while considering their potential applications.It has been established that there exists a correlation between the drought tolerance of maize lines and their relative resistance to aflatoxin contamination under hot and dry conditions[5,26].These conditions are also known to result in the accumulation of ROS in plant tissues,and, given that recent reports demonstrate that ROS can regulate aflatoxin production in Aspergillus spp.,this provides a potential link between aflatoxin production and host-derived oxidative stress[19,25,41,53].Therefore,if host derived oxidative stress inresponse to abiotic stress can possibly exacerbate aflatoxin production,the selection of components involved in antioxidant mechanism such as metabolites,proteins,and gene expression levels may allow them to be utilized as molecular markers,“biomarkers,”for use in selection in breeding applications.

    For instance,Pechanova et al.[18]reported that resistant maize lines accumulate high levels of superoxide dismutase, peroxidases,and chaperonins in rachis tissues.Such highly expressed proteins could be utilized for screening germplasm and populations for markers related to both aflatoxin resistance,as well as abiotic stress tolerance.Fountain et al.[54] reported that expression of the gene encoding the 14-kDa trypsin inhibitor known to inhibit fungal amylases,was highly expressed in kernel tissues of resistant maize lines compared to susceptible lines when infected by A.flavus under drought stress conditions.In addition,detoxifying enzymes such as glutathione-S-transferase(GST)and pathogenesis-related proteins such as PR-10 can also be used to screen for pathogen resistance or abiotic stress tolerance based on their respective biological activities[15,55,56].Genomic and proteomic expression studies during the infection process have indicated that oxidative stress tolerance is vital to adaptive changes in fungal biology during infection[57].Additional studies have also shown that maize lines with known resistance to drought and aflatoxin contamination are more recalcitrant to oxidative stress due to more stably expressed antioxidant components than susceptible lines[25].Therefore,these oxidative stress tolerance mechanisms may serve as sources for selectable markers for use in breeding applications for aflatoxin contamination resistance and drought tolerance.By combining these and additional“biomarkers”in conjunction with traditional genetic markers such as insertion/deletions(indels),single nucleotide polymorphisms(SNPs),or simple sequence repeat (SSR)/microsatellite markers,the efficiency of selecting resistant germplasm could be enhanced.In addition,by selecting“biomarkers”that provide both abiotic stress tolerance and aflatoxin resistance,some of the confounding effects of genotype×environment interactions may be avoided.Future studies should examine the utilization and feasibility of potential multi-purpose“biomarkers”for use in large scale marker assisted selection(MAS)applications.

    3.2.QTL discovery

    As previously stated,resistance to A.flavus colonization and aflatoxin contamination was demonstrated to be quantitative and heavily influenced by environmental interactions[5,9,58]. Therefore,recent breeding studies focused on the discovery and characterization of quantitative trait loci(QTL)for aflatoxin resistance were forced to consider the environment in obtaining phenotypic data,and have faced numerous challenges in identifying consistent QTL for aflatoxin resistance.For example, Willcox et al.[59]utilized an F2mapping population derived from Mp313E×Va35(resistant×susceptible)to identify 20 QTLs with combined phenotypic variance explained(PVE)of 22–43%. However,when the mapping populations were grown in multiple environments,only 11 QTLs were found to be consistent with a combined PVE of 2.4–9.5%.An earlier study by Brooks et al.[60] also examined a population derived from Mp313E for the presence of QTL for aflatoxin resistance.A collection of 210 F2:3families derived from Mp313E×B73(resistant×susceptible) was utilized for the study and a total of 85 polymorphic SSR markers was selected for genotyping and map construction.By analyzing phenotypic data from three locations,they were able to identify two consistent QTLs,one with a PVE of 7–18%,and a second with a PVE of 8–18%,indicating a nominal degree of variation between the environments.In another study,a single consistent QTL(PVE 8.42%)was identified using a recombinant inbred line(RIL)population of 228F8:9RILs derived from RA×M53(resistant×susceptible)utilizing 916 SNP markers for linkage map construction,and phenotyping data was obtained from two locations with contrasting environments for phenotypic analysis[61].

    These studies demonstrate that resistance to A.flavus is not conferred by a single gene and is highly quantitative in nature.In addition,given the relatively low level of PVE provided by each QTL,it is likely that many QTL with low PVE(<10%)contribute to aflatoxin resistance and may be indicative of the polygenic nature of resistance and the involvement of multiple physiological and morphological traits in the overall resistance phenotype [5,62].Interestingly,similar difficulties are also faced when examining drought tolerance QTL in maize.For example, Almeida et al.[63]recently performed a QTL analysis of drought tolerance in three populations:a RIL population derived from CML444×MALAWI,aF2:3family set derived from CML440×CML504,and a second F2:3family set derived from CML444×CML441.They identified QTLs for grain yield under drought stress with PVE ranging from 2.6–17.8%,and for the anthesis–silking interval under drought stress with a PVE ranging from 1.7–17.8%.Genome wide association studies (GWAS),which rely on ancient recombination events among diverse inbreeds for mapping QTL,are limited in their detection of QTL with low PVE,and may not identify aflatoxin resistance and drought tolerance QTL unless high numbers of individuals and markers are used to increase the resolving power of the experiment[62,64].

    Once identified,QTL function and composition must be determined in order to elucidate the mechanism being employed to produce a particular phenotype,namely aflatoxin resistance.In conjunction with QTL discovery in traditional bi-parental populations,the integration of functional genomics technologies has been shown to enhance QTL validation by confirming the expression and identity of genes present in QTL regions.A recent study by Kelley et al.[9]utilized microarray analysis to validate the expression of QTL-associated genes involved in A.flavus responses in the maize lines Mp313E and Va35.As this study illustrated,coupling functional genomics analysis with QTL discovery also allows the determination of the mechanism employed by maize in response to A.flavus infection by determining not only which genes within the QTL regions are regulated,but also whether they are up or down-regulated and the amount of regulation.Coupling expression and QTL studies with functional genetics,experiments can be conducted to determine the function of specific genes,such as pathogenesis-related defense genes through methods such as RNA interference-(RNAi)based gene silencing [14].These studies will provide for the identification of the causal basis of a gene contribution to a QTL and provide possible explanations for the influence of environment on the detection and stability of QTL.

    3.3.Applications of biomarkers and QTL in conventional breeding programs

    Conventional breeding for resistance has formed the basis of generating aflatoxin contamination-resistant maize lines with recent efforts in this field resulting in the release of several lines with promising levels of aflatoxin contamination resistance [23,65–67].As recently reviewed by Williams et al.[68],several aflatoxin resistant lines including GT601,GT602,GT603,Mp715, Mp717,Mp718,and Mp719 were derived from conventional breeding programs in the southeastern U.S.In addition,the incorporation of exotic lines with aflatoxin accumulation resistance and additional desirable traits into breeding programs to widen the genetic base of traditional temperate lines through cooperative efforts such as the Germplasm Enhancement of Maize(GEM)project will allow for further enhancement of previously identified resistant lines[68].In addition to variety development,recent research has also focused on the evaluating the general and specific combining abilities of aflatoxin resistant lines to enhance hybrid development.For example,Williams et al.[69]performed a diallel cross using ten inbred lines with varying levels of resistance to aflatoxin contamination including: CI66,GA209,NC408,Mo18W,Mp313E,Mp494,Mp715,Mp717, SC212m,and T173.They found that the resistant lines Mp313E, Mp494,Mp715,Mp717,Mo18W,and NC408 possessed significant general combining ability(GCA)effects for resistance to aflatoxin and proposed that utilizing GCA data to plan crosses in resistance breeding will expedite progress in developing aflatoxin resistant hybrids.

    This diallel study illustrates the potential utility of additional selection methodologies in enhancing aflatoxin resistance in maize.Currently,screening for aflatoxin resistance is carried out either in the field with directino culation which canproduce variable results depending on environmental conditions and the method used,or in the laboratory with kernel screening assays(KSAs)for high throughput screening[70].Given the potential for variability in these systems,the incorporation of molecular markers into breeding programs for use in MAS could provide for more consistent results.However,while many QTLs and associated polymorphic markers have been discovered in maize for resistance to aflatoxin contamination and A.flavus colonization,their utility in conventional breeding programs has been limited.This is likely due to the variable nature of the expression of these QTLs across multiple environments and conditions.Therefore,biomarkers selected based on their role in both aflatoxin resistance and abiotic stress responses may provide a method to account for environmental influences on aflatoxin resistance.When used in conjunction with traditional DNA-based marker systems and conventional resistance breeding,biomarkers may prove to valuable tools for breeder to enhance aflatoxin resistance and associated traits such as drought tolerance into improved germplasm.

    4.Correlating environmental stress and aflatoxin resistance in peanut

    Peanut(Arachis hypogaea L.)is an allotetraploid(2n=4x=40) crop grown in over 100 countries.One of the major concerns about the import/export of peanut is aflatoxin contamination (AC)which may result in the rejection of seed lots if levels of aflatoxin are above maximum prescribed limits[71].AC in peanut is caused by two fungal pathogens,A.flavus and A. parasiticus with A.flavus being the most prevalent in infected pods.A typical pattern of fungal infection includes entry of the fungi through small cracks developed during pod maturation/drying in the ground[72].

    Ithasbeen demonstrated that pre-harvest aflatoxin contamination(PAC)is increased when abiotic stress such as drought stress is imposed on the crop.This may be due to reduced water activity during pod development which could lead to the creation of cracks in the pod wall.Hence,damaged pods tend to be more susceptible to PAC than undamaged pods[73,74].Other studies point out that reduced kernel water content may decrease phytoalexin production thereby decreasing the plant's natural defense against infection leading to increased AC[75,76].In addition to drought stress,heat stress has also been found to play an important role in PAC [75,77].Apart from genetic sources of resistance in peanut, PAC management practices such as correct irrigation,fungicide applications,avoidance of mechanical damage,biological control,crop rotation,harvest timing,and good post-harvest storage conditions play critical roles in limiting AC in peanut [24,58].

    Drought stress seems to function as a predisposing factor for PAC in peanut[78,79].Therefore,a common idea arises that drought tolerant cultivars would assist in alleviating PAC, indicating that direct or indirect selection for PAC during drought tolerance would be appropriate.In order to understand the molecular mechanisms of aflatoxin biosynthesis,some genomic and proteomic studies have been carried out[80–83].A positive correlation was found between 20 drought tolerant lines and PAC resistance[84].Furthermore,the measures of several drought tolerance component traits such as SPAD (measured by a SPAD-502 meter:Minolta,Tokyo,Japan) chlorophyll meter reading(SCMR),and specific leaf area(SLA) also showed positive correlations with PAC resistance[73]. Conversely,the results of a recent study indicated that although drought tolerance increases PAC resistance in some lines,it does not universally apply to all genetic backgrounds.Hence, drought tolerance and resistance to PAC may involve different mechanisms in peanut[85].

    The lack of high levels of resistance to aflatoxin contamination in cultivated germplasm and a reliable phenotyping protocol,poses challenges in using conventional breeding methods to identify resistance to PAC in peanuts.Nevertheless,a large scale screening effort consisting of 831 accessions in the US peanut core collection led to the identification of 19 accessions with low PAC and relatively high yield[86].At the International Crops Research Institute for the Semi-Arid Tropics(ICRISAT)several resistant germplasms were identified for three types of resistance(i.e.PAC,resistance to in vitro seed colonization(IVSC),and aflatoxin production by A.flavus) after extensive screening of more than 2000 peanut accessions in a heavily infested field plot(“sick plot”)under conditions of imposed drought[87].

    Use of molecular markers for PAC resistance is very limited. For instance,a set of 6 amplified fragment length polymorphism(AFLP)markers with low PVE in Arachis cardenasii-derivedlines were identified[88]and in another study six QTLs for resistance to A.flavus infection with PVE up to 22.7%were identified[89].Since resistance to PAC is a global problem, an international effort was recently undertaken under the ambit of the Peanut&Mycotoxin Innovation Lab(PMIL) initiated with collaboration between ICRISAT,the University of Georgia(UGA),and Institut Sénégalais de Recherches Agricoles(ISRA)in Senegal.This effort utilizes RIL populations,association mapping panels,multiparent advanced generation intercross(MAGIC)populations,interspecific introgression lines,and genomic selection approaches in order to enhance our understanding of the genetic components of PAC.

    In summary,resistance to PAC in peanut is a complex trait with high G×E interaction,low heritability,and a lack of reliable phenotyping protocols.These limitations pose challenges in identifying and developing resistant germplasm.Unfortunately,there is no single,highly effective source of resistance that can be used to tackle this issue from a genetic perspective.Therefore,crop management in conjunction with enhanced genetic resistance should be the way forward for obtaining PAC resistance in peanut.

    5.Conclusions and future perspectives

    Resistance to A.flavus infection and aflatoxin contamination in maize and peanut is a complex trait that is heavily influenced by environmental factors.Current efforts in determining the biochemical basis of resistance and use of that knowledge in breeding programs has led to an increased understanding of elements of this plant–pathogen interaction.However,many questions remain to be answered as to the role of aflatoxin in the biology and ecology of Aspergillus spp.and its role in pathogenesis,including the role of aflatoxin as a source of cellular oxidative stress.In addition,the potential role of host-derived ROS in stimulating aflatoxin production is also in need of further study.Future work should also address the potential use of identified proteins,metabolites,and candidate genes as selectable biomarkers for use in MAS.By utilizing such markers,breeding programs can be optimizedto select not only for aflatoxin resistance but also for associated abiotic stress tolerance.

    Acknowledgments

    This work was partially supported by the U.S.Department of Agriculture Agricultural Research Service(USDA-ARS), the Georgia Agricultural Commodity Commission for Corn, the Georgia Peanut Commission,Peanut Foundation and AMCOE(Aflatoxin Mitigation Center of Excellence).The work was undertaken as part of the CGIAR Research Program on Grain Legumes.ICRISAT is a member of CGIAR Consortium. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA.The USDA is an equal opportunity provider and employer.

    [1]B.W.Horn,G.G.Moore,I.Carbone,Sexual reproduction in Aspergillus flavus,Mycologia 101(2009)423–429.

    [2]B.W.Horn,J.H.Ramirez-Prado,I.Carbone,The sexual state of Aspergillus parasiticus,Mycologia 101(2009)275–280.

    [3]U.L.Diener,R.J.Cole,T.H.Sanders,G.A.Payne,S.Lee,M.A. Klich,Epidemiology of aflatoxin formation by Aspergillus flavus,Annu.Rev.Phytopathol.25(1987)249–270.

    [4]F.Wu,P.Khlangwiset,Health economic impacts and cost-effectiveness of aflatoxin reduction strategies in Africa: case studies in biocontrol and postharvest interventions, Food Addit.Contam.A 27(2010)496–509.

    [5]J.C.Fountain,B.T.Scully,X.Ni,R.C.Kemerait,R.D.Lee,Z.Y. Chen,B.Z.Guo,Environmental influences on maize–Aspergillus flavus interactions and aflatoxin production,Front.Microbiol.5 (2014)1–7.

    [6]G.S.Shephard,Impact of mycotoxins on human health in developing countries,Food Addit.Contam.A 25(2008) 146–151.

    [7]C.P.Wild,Y.Y.Gong,Mycotoxins and human disease:a largely ignored global health issue,Carcinogenesis 31(2010)71–82.

    [8]S.Amaike,N.P.Keller,Aspergillus flavus,Annu.Rev. Phytopathol.49(2011)107–133.

    [9]R.Y.Kelley,W.P.Williams,J.E.Mylroie,D.L.Boykin,J.W. Harper,G.L.Windham,A.Ankala,X.Shan,Identification of maize genes associated with host plant resistance or susceptibility to Aspergillus flavus infection and aflatoxin accumulation,PLoS ONE 7(2012)5.

    [10]X.Liang,M.Luo,B.Z.Guo,Resistance mechanisms to Aspergillus flavus infection and aflatoxin contamination in peanut(Arachis hypogaea),Plant Pathol.J.5(2006)115–124.

    [11]P.Chadha,R.H.Das,A pathogenesis related protein,AhPR10 from peanut:an insight of its mode of antifungal activity, Planta 225(2006)213–222.

    [12]Z.Y.Chen,R.L.Brown,K.E.Damann,T.E.Cleveland, Identification of a maize kernel stress-related protein and its effect on aflatoxin accumulation,Phytopathology 94(2004) 938–945.

    [13]Z.Y.Chen,R.L.Brown,A.R.Lax,B.Z.Guo,T.E.Cleveland,J.S. Russin,Resistance to Aspergillus flavus in corn kernels is associated with a 14-kDa protein,Phytopathology 88(1998) 276–281.

    [14]Z.Y.Chen,R.L.Brown,A.Menkir,T.E.Cleveland,Identification of resistance-associated proteins in closely-related maize lines varying in aflatoxin accumulation,Mol.Breed.30(2012)53–68.

    [15]Z.Y.Chen,R.L.Brown,K.Rajasekaran,K.E.Damann,T.E. Cleveland,Identification of a maize kernel pathogenesis-related protein and evidence for its involvement in resistance to Aspergillus flavus infection and aflatoxin production, Phytopathology 96(2006)87–95.

    [16]Z.Y.Chen,R.L.Brown,J.S.Russin,A.R.Lax,T.E.Cleveland,A corn trypsin inhibitor with antifungal activity inhibits Aspergillus flavus α-amylase,Phytopathology 89(1999) 902–907.

    [17]K.G.Moore,M.S.Price,R.S.Boston,A.K.Weissinger,G.A. Payne,A chitinase from Tex6 maize kernels inhibits growth of Aspergillus flavus,Phytopathology 94(2004)82–87.

    [18]O.Pechanova,T.Pechan,W.P.Williams,D.S.Luthe, Proteomic analysis of the maize rachis:potential roles of constitutive and induced proteins in resistance to Aspergillus flavus infection and aflatoxin accumulation,Proteomics 11 (2011)114–127.

    [19]L.V.Roze,S.Y.Hong,J.E.Linz,Aflatoxin biosynthesis:current frontiers,Annu.Rev.Food Sci.Tech.4(2013)293–311.

    [20]T.Wang,X.-P.Chen,H.-F.Li,H.-Y.Liu,Y.-B.Hong,Q.-L.Yang, X.-Y.Chi,Z.Yang,S.-L.Yu,L.Li,X.-Q.Liang,Transcriptome identification of the resistance-associated genes(RAGs)toAspergillus flavus infection in pre-harvested peanut(Arachis hypogaea),Funct.Plant Biol.40(2013)292–303.

    [21]B.Z.Guo,Z.Y.Chen,R.D.Lee,B.T.Scully,Drought stress and preharvest aflatoxin contamination in agricultural commodities:genetics,genomics and proteomics,J.Int. Plant Biol.50(2008)1281–1291.

    [22]T.Jiang,J.Fountain,G.Davis,R.Kemerait,B.Scully,R.D.Lee, B.Guo,Root morphology and gene expression analysis in response to drought stress in maize(Zea mays),Plant Mol. Biol.Report.30(2012)360–369.

    [23]B.T.Scully,M.D.Krakowsky,X.Ni,J.P.Wilson,R.D.Lee,B.Z. Guo,Preharvest aflatoxin contamination of corn and other grain crops grown on the U.S.Southeastern Coastal Plain, Toxin Rev.28(2009)169–179.

    [24]A.M.Torres,G.G.Barros,S.A.Palacios,S.N.Chulze,P. Battilani,Review on pre-and post-harvest management of peanuts to minimize aflatoxin contamination,Food Res.Int. 62(2014)11–19.

    [25]L.Yang,J.C.Fountain,T.Jiang,B.T.Scully,R.D.Lee,R.C. Kemerait,S.Chen,B.Guo,Protein profiles reveal diverse drought-responsive signaling pathways in maize kernels,Int. J.Mol.Sci.15(2014)18892–18918.

    [26]B.Z.Guo,J.Yu,X.Ni,R.D.Lee,R.C.Kemerait,B.T.Scully,Crop stress and aflatoxin contamination:perspectives and prevention strategies,in:B.Venkateswarlu,A.K.Shankerk, C.Shanker,M.Makeswari(Eds.),Crop Stress and Its Management:Perspectives and Strategies,Springer,New York 2012,pp.399–427.

    [27]J.C.Fountain,Y.Raruang,M.Luo,R.L.Brown,B.Z.Guo,Z.Y. Chen,Potential roles of WRKY transcription factors in regulating host defense responses during Aspergillus flavus infection of immature maize kernels,Physiol.Mol.Plant Pathol.89(2015)31–40.

    [28]P.J.Rushton,I.E.Somssich,P.Ringler,Q.J.Shen,WRKY transcription factors,Trends Plant Sci.15(2010)247–258.

    [29]Y.Miao,T.Laun,P.Zimmermann,U.Zentgraf,Targets of the WRKY53 transcription factor and its role during leaf senescence in Arabidopsis,Plant Mol.Biol.55(2004) 853–867.

    [30]S.C.Popescu,G.V.Popescu,S.Bachan,Z.Zhang,M.Seay,M. Gerstein,M.Snyder,S.P.Dinesh-Kumar,Differential binding of calmodulin-related proteins to their targets revealed through high-density Arabidopsis protein microarrays,Proc. Natl.Acad.Sci.U.S.A.104(2007)4730–4735.

    [31]H.Li,Y.Gao,H.Xu,Y.Dai,D.Deng,J.Chen,ZmWRKY33,a WRKY maize transcription factor conferring enhanced salt stress tolerances in Arabidopsis,Plant Growth Regul.70(2013) 207–216.

    [32]S.K.Bera,B.C.Ajay,A.L.Singh,WRKY and Na+/H+antiporter genes conferring tolerance to salinity in interspecific derivatives of peanut(Arachis hypogaea L.),Aust.J.Crop.Sci.7 (2013)1173–1180.

    [33]S.S.Gill,N.Tuteja,Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants,Plant Physiol.Biochem.48(2010)909–930.

    [34]T.Eulgem,I.E.Somssich,Networks of WRKY transcription factors in defense signaling,Curr.Opin.Plant Biol.10(2007) 366–371.

    [35]Y.Miao,T.M.Laun,A.Smykowski,U.Zentgraf,Arabidopsis MEKK1 can take a short cut:it can directly interact with senescence-related WRKY53 transcription factor on the protein level and can bind to its promoter,Plant Mol.Biol.65 (2007)63–76.

    [36]J.Wan,S.Zhang,G.Stacey,Activation of a mitogen-activated protein kinase pathway in Arabidopsis by chitin,Mol.Plant Pathol.5(2004)125–135.

    [37]B.Zhang,K.Ramonell,S.Somerville,G.Stacey,Characterization of early,chitin-induced gene expression in Arabidopsis,Mol. Plant-Microbe Interact.15(2002)963–970.

    [38]W.Ma,G.A.Berkowitz,Ca2+conduction by plant cyclic nucleotide gated channels and associated signaling components in pathogen defense signal transduction cascades,New Phytol.190(2011)566–572.

    [39]M.Jiang,J.Zhang,Cross-talk between calcium and reactive oxygen species originated from NADPH oxidase in abscisic acid-induced antioxidant defence in leaves of maize seedlings,Plant Cell Environ.26(2003)929–939.

    [40]X.Hu,M.Jiang,J.Zhang,A.Zhang,F.Lin,M.Tan, Calcium–calmodulin is required for abscisic acid-induced antioxidant defense and functions both upstream and downstream of H2O2production in leaves of maize(Zea mays)plants,New Phytol.173(2007)27–38.

    [41]L.V.Roze,A.Chanda,J.Wee,D.Awad,J.E.Linz,Stress-related transcription factor AtfB integrates secondary metabolism with oxidative stress response in aspergilla,J.Biol.Chem.286 (2011)35137–35148.

    [42]K.J.Affeldt,M.Brodhagen,N.P.Keller,Aspergillus oxylipin signaling and quorum sensing pathways depend on G protein-coupled receptors,Toxins 4(2012)695–717.

    [43]X.Gao,M.V.Kolomiets,Host-derived lipids and oxylipins are crucial signals in modulating mycotoxin production by fungi, Toxin Rev.28(2009)79–88.

    [44]C.M.Grice,M.Bertuzzi,E.M.Bignell,Receptor-mediated signaling in Aspergillus fumigatus,Front.Microbiol.4(2013)26.

    [45]A.Chanda,L.V.Roze,S.Kang,K.A.Artymovich,G.R.Hicks, N.V.Raikhel,A.M.Calvo,J.E.Linz,A key role for vesicles in fungal secondary metabolism,Proc.Natl.Acad.Sci.U.S.A. 106(2009)19533–19538.

    [46]A.Chanda,L.V.Roze,J.E.Linz,Aflatoxin export in Aspergillus parasiticus:a possible role for exocytosis,Eukaryot.Cell 9 (2010)1724–1727.

    [47]J.E.Linz,A.Chanda,S.Y.Hong,D.A.Whitten,C.Wilkerson, L.V.Roze,Proteomic and biochemical evidence support a role for transport vesicles and endosomes in stress response and secondary metabolism in Aspergillus parasiticus,J.Proteome Res.11(2011)767–775.

    [48]L.V.Roze,A.Chanda,J.E.Linz,Compartmentalization and molecular traffic in secondary metabolism:a new understanding of established cellular processes,Fungal Genet.Biol.48(2011)35–48.

    [49]L.L.Bedard,T.E.Massey,Aflatoxin B1-induced DNA damage and its repair,Cancer Lett.241(2006)174–183.

    [50]F.P.Guengerich,W.W.Johnson,T.Shimada,Y.F.Ueng,H. Yamazaki,S.Langou?t,Activation and detoxication of aflatoxin B1,Mutat.Res.402(1998)121–128.

    [51]N.Jameson,N.Georgelis,E.Fouladbash,S.Martens,L.C. Hannah,S.Lal,Helitron mediated amplification of cytochrome P450 monooxygenase gene in maize,Plant Mol.Biol.67(2008) 295–304.

    [52]S.X.Mideros,G.L.Windham,W.P.Williams,R.J.Nelson, Aspergillus flavus biomass in maize estimated by quantitative real-time polymerase chain reaction is strongly correlated with aflatoxin concentration,Plant Dis.93(2009)1163–1170.

    [53]M.Farooq,A.Wahid,N.Kobayashi,D.Fujita,S.M.A.Basra, Plant drought:effects,mechanisms,and management, Agron.Sustain.Dev.29(2009)185–212.

    [54]J.C.Fountain,Z.Y.Chen,B.T.Scully,R.C.Kemerait,R.D.Lee, B.Z.Guo,Pathogenesis-related gene expressions in different maize genotypes under drought stressed conditions,Afr.J. Plant Sci.4(2010)433–440.

    [55]M.Hajheidari,A.Eivazi,B.B.Buchanan,J.H.Wong,I.Majidi, G.H.Salekdeh,Proteomics uncovers a role for redox in drought tolerance in wheat,J.Proteome Res.6(2007) 1451–1460.

    [56]A.Kakumanu,M.M.Ambavaram,C.Klumas,A.Krishnan,U. Batlang,E.Myers,R.Grene,A.Pereira,Effects of drought on gene expression in maize reproductive and leaf meristem tissue revealed by RNA-Seq,Plant Physiol.160(2012)846–867.

    [57]M.Reverberi,M.Punelli,V.Scala,M.Scarpari,P.Uva,W.I. Mentzen,A.L.Dolezal,C.Woloshuk,F.Pinzari,A.A.Fabbri,C. Fanelli,G.A.Payne,Genotypic and phenotypic versatility of Aspergillus flavus during maize exploitation,PLoS ONE 8(2013) (e68735).

    [58]B.Z.Guo,N.W.Widstrom,R.D.Lee,D.M.Wilson,A.E.Coy, Prevention of preharvest aflatoxin contamination:integration of crop management and genetics in corn,in:H.Abbas(Ed.), Aflatoxin and Food Safety,CRC Press,Boca Raton,Florida 2005, pp.437–457.

    [59]M.C.Willcox,G.L.Davis,M.L.Warburton,G.L.Windham,H.K. Abbas,J.Betrán,J.B.Holland,W.P.Williams,Confirming quantitative trait loci for aflatoxin resistance from Mp313E in different genetic backgrounds,Mol.Breed.32(2013)15–26.

    [60]T.D.Brooks,W.P.Williams,G.L.Windham,M.C.Willcox,H.K. Abbas,Quantitative trait loci contributing resistance to aflatoxin accumulation in maize inbred Mp313E,Crop Sci.45 (2005)171–174.

    [61]Z.Yin,Y.Wang,F.Wu,X.Gu,Y.Bian,Y.Wang,D.Deng, Quantitative trait locus mapping of resistance to Aspergillus flavus infection using a recombinant inbred line population in maize,Mol.Breed.33(2014)39–49.

    [62]M.L.Warburton,W.P.Williams,Aflatoxin resistance in maize:what have we learned lately?Adv.Bot.2014(2014)10.

    [63]G.D.Almeida,D.Makumbi,C.Magorokosho,S.Nair,A. Borém,J.M.Ribaut,M.B?nziger,B.M.Prasanna,J.Crossa,R. Babu,QTL mapping in three tropical maize populations reveals a set of constitutive and adaptive genomic regions for drought tolerance,Theor.Appl.Genet.126(2013)583–600.

    [64]P.M.Visscher,D.Posthuma,Statistical power to detect genetic loci affecting environmental sensitivity,Behav. Genet.40(2010)728–733.

    [65]B.Z.Guo,M.D.Krakowsky,X.Ni,B.T.Scully,R.D.Lee,A.E.Coy, N.W.Widstrom,Registration of maize inbred line GT603,J. Plant Regist.5(2011)211–214.

    [66]B.Z.Guo,N.W.Widstrom,R.D.Lee,A.E.Coy,R.E.Lynch, Registration of maize germplasm GT601(AM-1)and GT602 (AM-2),J.Plant Regist.1(2007)153–154.

    [67]B.T.Scully,M.D.Krakowsky,X.Ni,P.J.Tapp,J.K.Knoll,R.D. Lee,B.Z.Guo,Registration of maize inbred line‘GT888’,J. Plant Regist.9(2015)(in press).

    [68]W.P.Williams,M.D.Krakowsky,B.T.Scully,R.L.Brown,A. Menkir,M.L.Warburton,G.L.Windham,Identifying and developing maize germplasm with resistance to accumulation of aflatoxins,World Mycotoxin J.8(2014)193–209.

    [69]W.P.Williams,G.L.Windham,P.M.Buckley,Diallele analysis of aflatoxin accumulation in maize,Crop Sci.48(2008) 134–138.

    [70]R.L.Brown,A.Menkir,Z.Y.Chen,D.Bhatnagar,J.Yu,H.Yao, T.E.Cleveland,Breeding aflatoxin-resistant maize lines using recent advances in technologies—a review,Food Addit. Contam.A 30(2013)1382–1391.

    [71]J.M.Wagacha,J.W.Muthomi,Mycotoxin problems in Africa: current status,implications to food safety and health and possible management strategies,Int.J.Food Microbiol.124 (2008)1–12.

    [72]T.H.Sanders,P.D.Blankenship,R.J.Cole,R.A.Hill,Effect of soil temperature and drought on peanut pod and stem temperatures relative to Aspergillus flavus invasion and aflatoxin contamination,Mycopathologia 86(1984)51–54.

    [73]T.Girdthai,S.Jogloy,N.Vorasoot,C.Akkasaeng,S. Wongkaew,C.C.Holbrook,A.Patanothai,Associations between physiological traits for drought tolerance and aflatoxin contamination in peanut genotypes under terminal drought,Plant Breed.129(2010)693–699.

    [74]P.Sudhakar,P.Lathat,M.Babitha,P.V.Reddy,P.H.Naidu, Relationship of drought tolerance traits with aflatoxin contamination in groundnut,Indian J.Plant Physiol.12(2007) 261–265.

    [75]J.Dorner,R.Cole,T.Sanders,P.Blankenship,Interrelationship of kernel water activity,soil temperature,maturity,and phytoalexin production in pre-harvest aflatoxin contamination of drought-stressed peanuts,Mycopathologia 105(1989)117–128.

    [76]J.I.Pitt,M.H.Taniwaki,M.B.Cole,Mycotoxin production in major crops as influenced by growing,harvesting,storage and processing,with emphasis on the achievement of Food Safety Objectives,Food Control 32(2013)205–215.

    [77]S.D.Golombek,C.Johasen,Effect of soil temperature on vegetative and reproductive growth and development in three Spanish genotypes of groundnut(Arachis hypogaea L.), Peanut Sci.24(1997)67–72.

    [78]A.Arunyanark,S.Jogloy,S.Wongkaew,C.Akkasaeng,N. Vorasoot,G.C.Wright,R.C.N.Rachaputi,A.Patanothai, Association between aflatoxin contamination and drought tolerance traits in peanut,Field Crop Res.114(2009)14–22.

    [79]T.Girdthai,S.Jogloy,N.Vorasoot,C.Akkasaeng,S. Wongkaew,C.C.Holbrook,A.Patanothai,Heritability of,and genotypic correlations between,aflatoxin traits and physiological traits for drought tolerance under end of season drought in peanut(Arachis hypogaea L.),Field Crops Res.118 (2010)169–176.

    [80]B.Z.Guo,J.Yu,C.C.Holbrook,T.E.Cleveland,W.C.Nierman, B.T.Scully,Strategies in prevention of preharvest aflatoxin contamination in peanuts:aflatoxin biosynthesis,genetics and genomics,Peanut Sci.36(2009)11–20.

    [81]B.Z.Guo,C.Y.Chen,Y.Chu,C.C.Holbrook,P.Ozias-Akins, H.T.Stalker,Advances in genetics and genomics for sustainable peanut production,in:N.Benkeblia(Ed.), Sustainable Agriculture and New Biotechnologies,CRC Press,Boca Raton,Florida 2012,pp.341–367.

    [82]T.Wang,E.H.Zhang,X.P.Chen,L.Li,X.Q.Liang,Identification of seed proteins associated with resistance to pre-harvested aflatoxin contamination in peanut(Arachis hypogaea L.),BMC Plant Biol.10(2010)267–278.

    [83]Z.Wang,S.Yan,C.Liu,F.Chen,T.Wang,Proteomic analysis reveals an aflatoxin-triggered immune response in cotyledons of Arachis hypogaea infected with Aspergillus flavus,J.Proteome 11(2012)2739–2753.

    [84]C.C.Holbrook,C.K.Kvien,K.S.Rucker,D.W.Wilson,J.E.Hook, Preharvest aflatoxin contamination in drought tolerant and intolerant peanut genotypes,Peanut Sci.27(2000)45–48.

    [85]F.Hamidou,A.Rathore,F.Waliyar,V.Vadez,Although drought intensity increases aflatoxin contamination,drought tolerance does not lead to less aflatoxin contamination,Field Crops Res.156(2014)103–110.

    [86]C.C.Holbrook,B.Z.Guo,D.M.Wilson,P.Timper,The U.S. breeding program to develop peanut with drought tolerance and reduced aflatoxin contamination,Peanut Sci.36(2009) 50–53.

    [87]S.N.Nigam,F.Waliyar,R.Aruna,S.V.Reddy,P.L.Kumar,P.Q. Craufurd,A.T.Diallo,B.R.Ntare,H.D.Upadhyaya,Breeding peanut for resistance to aflatoxin contamination at ICRISAT, Peanut Sci.36(2009)42–49.

    [88]S.R.Milla,T.G.Isleib,S.P.Tallury,Identification of AFLP markers linked to reduced aflatoxin accumulation in A. cardenasii-derived germplasm lines of peanut,Proc.Am. Peanut Res.Educ.Soc.37(2005)90.

    [89]X.Liang,G.Zhou,Y.Hong,X.Chen,H.Liu,S.Li,Overview of research progress on peanut(Arachis hypogaea L.)host resistance to aflatoxin contamination and genomics at the Guangdong Academy of Agricultural Sciences,Peanut Sci.36 (2009)29–34.

    *Corresponding author.

    E-mail address:baozhu.guo@ars.usda.gov(B.Guo).

    Peer review under responsibility of Crop Science Society of China and Institute of Crop Science,CAAS.

    http://dx.doi.org/10.1016/j.cj.2015.02.003

    2214-5141/?2015 Crop Science Society of China and Institute of Crop Science,CAAS.Production and hosting by Elsevier B.V.All rights reserved.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

    在线免费观看不下载黄p国产| 有码 亚洲区| 两个人的视频大全免费| 日韩欧美一区视频在线观看 | 久久久久久伊人网av| 国产一区二区三区av在线| 日本与韩国留学比较| 在线观看av片永久免费下载| 看十八女毛片水多多多| 成人免费观看视频高清| 亚洲最大成人中文| 亚洲自拍偷在线| 激情五月婷婷亚洲| 麻豆乱淫一区二区| 免费av观看视频| 国产成人精品久久久久久| 亚洲伊人久久精品综合| 亚洲综合精品二区| 精品亚洲乱码少妇综合久久| 三级男女做爰猛烈吃奶摸视频| 亚洲精品成人久久久久久| 噜噜噜噜噜久久久久久91| 亚洲欧美中文字幕日韩二区| 国产探花在线观看一区二区| 天堂中文最新版在线下载 | a级毛色黄片| 99久久精品一区二区三区| 欧美xxⅹ黑人| 国产成人福利小说| 亚洲精品第二区| 成年女人在线观看亚洲视频 | a级毛色黄片| 欧美高清成人免费视频www| 日韩欧美 国产精品| 爱豆传媒免费全集在线观看| 在线 av 中文字幕| 成人一区二区视频在线观看| 中文天堂在线官网| 久久久精品94久久精品| 人妻系列 视频| 国产在线男女| 亚洲精品,欧美精品| 国产一区二区亚洲精品在线观看| 秋霞在线观看毛片| 在线精品无人区一区二区三 | 午夜免费鲁丝| 成年免费大片在线观看| 在线播放无遮挡| 亚洲精品乱码久久久久久按摩| 一边亲一边摸免费视频| 免费在线观看成人毛片| 在线精品无人区一区二区三 | 丝袜美腿在线中文| 亚洲图色成人| 插逼视频在线观看| av又黄又爽大尺度在线免费看| 插阴视频在线观看视频| 青春草视频在线免费观看| 日本-黄色视频高清免费观看| 日日撸夜夜添| 久久久久精品性色| 亚洲欧美成人精品一区二区| 自拍偷自拍亚洲精品老妇| 亚洲最大成人av| 亚洲精品第二区| 欧美高清成人免费视频www| 国产极品天堂在线| 国精品久久久久久国模美| 如何舔出高潮| 有码 亚洲区| 男插女下体视频免费在线播放| 最近最新中文字幕大全电影3| 精品国产一区二区三区久久久樱花 | 免费人成在线观看视频色| 麻豆久久精品国产亚洲av| 亚洲av福利一区| 男人爽女人下面视频在线观看| 精品一区二区三卡| 日产精品乱码卡一卡2卡三| 国产高清国产精品国产三级 | 尾随美女入室| 国内揄拍国产精品人妻在线| 久久国内精品自在自线图片| 亚洲人成网站高清观看| 男人舔奶头视频| 一级片'在线观看视频| 一区二区三区免费毛片| 久久99热6这里只有精品| 免费看不卡的av| 国产精品一区二区三区四区免费观看| 黄片wwwwww| 亚洲,一卡二卡三卡| 中文字幕亚洲精品专区| 免费观看av网站的网址| 亚洲欧洲日产国产| 成年免费大片在线观看| 国产老妇女一区| 免费电影在线观看免费观看| 亚洲人与动物交配视频| 五月开心婷婷网| 国产精品秋霞免费鲁丝片| 18禁裸乳无遮挡免费网站照片| 国产综合懂色| 亚洲av中文av极速乱| 青春草亚洲视频在线观看| 啦啦啦啦在线视频资源| 在线a可以看的网站| 国产精品一及| 人妻系列 视频| 伊人久久精品亚洲午夜| 一本—道久久a久久精品蜜桃钙片 精品乱码久久久久久99久播 | 三级经典国产精品| 中文精品一卡2卡3卡4更新| 国产老妇伦熟女老妇高清| 国产欧美日韩精品一区二区| 深夜a级毛片| 国产av国产精品国产| 高清毛片免费看| 国产老妇女一区| 国产成人精品婷婷| 啦啦啦啦在线视频资源| 成年版毛片免费区| 日本猛色少妇xxxxx猛交久久| 狂野欧美激情性bbbbbb| 九草在线视频观看| av免费在线看不卡| 国产淫片久久久久久久久| 亚洲精品一二三| 精品人妻视频免费看| 91久久精品国产一区二区成人| 亚洲av在线观看美女高潮| 高清午夜精品一区二区三区| 亚洲精品国产色婷婷电影| 国产亚洲一区二区精品| 精品酒店卫生间| 美女国产视频在线观看| 国产精品国产三级国产专区5o| 亚洲在久久综合| 日韩不卡一区二区三区视频在线| 亚洲精品国产av成人精品| 亚洲三级黄色毛片| 哪个播放器可以免费观看大片| 男男h啪啪无遮挡| 老师上课跳d突然被开到最大视频| 欧美精品一区二区大全| 亚洲欧美日韩卡通动漫| 男女无遮挡免费网站观看| freevideosex欧美| 一二三四中文在线观看免费高清| av专区在线播放| 日日啪夜夜撸| 嫩草影院新地址| 久久精品国产鲁丝片午夜精品| 免费观看在线日韩| 久久久久久国产a免费观看| 亚洲成人一二三区av| 三级男女做爰猛烈吃奶摸视频| 大片电影免费在线观看免费| 国产v大片淫在线免费观看| 国产老妇女一区| 久久久久久国产a免费观看| 久热久热在线精品观看| 精品熟女少妇av免费看| 久久综合国产亚洲精品| 天堂网av新在线| 男人舔奶头视频| 一二三四中文在线观看免费高清| 久久这里有精品视频免费| 国产黄色免费在线视频| 丰满少妇做爰视频| 久久久精品免费免费高清| 亚洲欧美日韩无卡精品| 麻豆成人午夜福利视频| 亚洲成色77777| 国产成人精品婷婷| 亚洲人成网站在线播| 成年女人看的毛片在线观看| 中国国产av一级| 熟妇人妻不卡中文字幕| 国产乱人视频| 亚洲国产欧美人成| 日本三级黄在线观看| 久久久久久九九精品二区国产| 超碰av人人做人人爽久久| 新久久久久国产一级毛片| 欧美精品人与动牲交sv欧美| 性插视频无遮挡在线免费观看| 国产免费又黄又爽又色| 精品久久久久久久久亚洲| 久久久久九九精品影院| 欧美激情国产日韩精品一区| 午夜激情久久久久久久| 亚洲av在线观看美女高潮| 在线观看av片永久免费下载| 18禁裸乳无遮挡免费网站照片| 国产又色又爽无遮挡免| 我的女老师完整版在线观看| 男人狂女人下面高潮的视频| 国产高潮美女av| 校园人妻丝袜中文字幕| tube8黄色片| 国产黄频视频在线观看| 婷婷色综合www| 亚洲欧美成人精品一区二区| 久久人人爽人人爽人人片va| 亚洲不卡免费看| 1000部很黄的大片| 国模一区二区三区四区视频| 日本熟妇午夜| 男女国产视频网站| 亚洲人成网站高清观看| 亚洲欧美成人综合另类久久久| 男人爽女人下面视频在线观看| 免费大片黄手机在线观看| 2018国产大陆天天弄谢| 男人舔奶头视频| 天天躁日日操中文字幕| 高清视频免费观看一区二区| 国产成年人精品一区二区| 一级av片app| kizo精华| 精品国产三级普通话版| 男男h啪啪无遮挡| 在线亚洲精品国产二区图片欧美 | 麻豆乱淫一区二区| 国产高潮美女av| 午夜福利视频精品| 国产探花极品一区二区| 欧美少妇被猛烈插入视频| 啦啦啦啦在线视频资源| 身体一侧抽搐| 97热精品久久久久久| 中文资源天堂在线| 各种免费的搞黄视频| 婷婷色av中文字幕| 三级国产精品欧美在线观看| 亚洲色图综合在线观看| 人妻一区二区av| 自拍欧美九色日韩亚洲蝌蚪91 | 久久精品国产亚洲网站| 国产精品一区二区性色av| 久久精品久久精品一区二区三区| 中文资源天堂在线| 欧美国产精品一级二级三级 | 亚洲国产成人一精品久久久| 午夜福利高清视频| 日本一二三区视频观看| 国产高清不卡午夜福利| 国精品久久久久久国模美| 人妻 亚洲 视频| 亚洲美女视频黄频| 国产精品久久久久久精品古装| 国产成人精品久久久久久| 一二三四中文在线观看免费高清| 99re6热这里在线精品视频| 亚洲自偷自拍三级| 亚洲精品一区蜜桃| 日本色播在线视频| 麻豆精品久久久久久蜜桃| 全区人妻精品视频| 王馨瑶露胸无遮挡在线观看| 亚洲最大成人中文| 一级毛片久久久久久久久女| 赤兔流量卡办理| 亚洲av男天堂| 亚洲人成网站在线播| 日产精品乱码卡一卡2卡三| 热99国产精品久久久久久7| 久久鲁丝午夜福利片| 久久久久久久午夜电影| 成年女人在线观看亚洲视频 | 少妇的逼水好多| 国产成人91sexporn| 久久精品久久久久久久性| 大话2 男鬼变身卡| 禁无遮挡网站| 高清午夜精品一区二区三区| 欧美日韩国产mv在线观看视频 | 成人黄色视频免费在线看| 亚洲国产精品成人久久小说| 肉色欧美久久久久久久蜜桃 | 欧美xxⅹ黑人| 日韩免费高清中文字幕av| 伊人久久精品亚洲午夜| 中国国产av一级| 成年女人在线观看亚洲视频 | 欧美 日韩 精品 国产| 免费看不卡的av| 老司机影院毛片| 亚洲成色77777| 国产精品国产三级专区第一集| 一本色道久久久久久精品综合| 能在线免费看毛片的网站| 极品少妇高潮喷水抽搐| 老司机影院毛片| 免费不卡的大黄色大毛片视频在线观看| 91在线精品国自产拍蜜月| 91精品国产九色| 五月开心婷婷网| 视频区图区小说| 最近中文字幕高清免费大全6| 丝瓜视频免费看黄片| 夫妻性生交免费视频一级片| 亚洲伊人久久精品综合| 婷婷色综合www| 久久精品国产鲁丝片午夜精品| videossex国产| 别揉我奶头 嗯啊视频| www.av在线官网国产| 免费av毛片视频| 久久97久久精品| 青春草国产在线视频| 亚洲精华国产精华液的使用体验| 亚洲一区二区三区欧美精品 | 亚洲美女搞黄在线观看| 伦理电影大哥的女人| 少妇丰满av| 午夜福利视频1000在线观看| 99久久精品一区二区三区| 91午夜精品亚洲一区二区三区| 久久久久久久久大av| 美女cb高潮喷水在线观看| 99久久人妻综合| 99视频精品全部免费 在线| 色视频在线一区二区三区| 国产精品人妻久久久久久| 男女边吃奶边做爰视频| 赤兔流量卡办理| 亚洲内射少妇av| 国产色婷婷99| 国产成人福利小说| 精品久久久久久久人妻蜜臀av| xxx大片免费视频| av黄色大香蕉| 久久久成人免费电影| 九九爱精品视频在线观看| 欧美日韩视频精品一区| 成人二区视频| 久久精品国产自在天天线| 美女高潮的动态| 亚洲av国产av综合av卡| 少妇熟女欧美另类| 亚洲真实伦在线观看| 亚洲欧美日韩另类电影网站 | 美女主播在线视频| 欧美 日韩 精品 国产| 久久国产乱子免费精品| 久热久热在线精品观看| 26uuu在线亚洲综合色| 日本黄色片子视频| 亚洲成人中文字幕在线播放| 精品99又大又爽又粗少妇毛片| 91aial.com中文字幕在线观看| 秋霞在线观看毛片| 国产午夜精品久久久久久一区二区三区| 亚洲成人久久爱视频| 国产精品一区二区性色av| 在现免费观看毛片| 在线观看av片永久免费下载| 麻豆乱淫一区二区| 深夜a级毛片| 亚洲精品456在线播放app| 国产真实伦视频高清在线观看| 日本黄色片子视频| 精品久久久久久久久亚洲| 亚洲国产成人一精品久久久| 国产精品av视频在线免费观看| 欧美 日韩 精品 国产| 五月伊人婷婷丁香| 最近最新中文字幕免费大全7| 久热久热在线精品观看| 成人国产麻豆网| 18禁动态无遮挡网站| 久久国产乱子免费精品| 亚洲久久久久久中文字幕| 久久精品国产自在天天线| 秋霞在线观看毛片| 两个人的视频大全免费| 好男人在线观看高清免费视频| 熟女电影av网| 少妇猛男粗大的猛烈进出视频 | 日本爱情动作片www.在线观看| 日韩国内少妇激情av| 国产高清有码在线观看视频| 人人妻人人澡人人爽人人夜夜| 亚洲婷婷狠狠爱综合网| 国产有黄有色有爽视频| av女优亚洲男人天堂| 国产女主播在线喷水免费视频网站| 久久久久精品性色| 亚洲真实伦在线观看| 麻豆成人午夜福利视频| 汤姆久久久久久久影院中文字幕| 一级av片app| 黄片wwwwww| 亚洲精品乱码久久久v下载方式| 草草在线视频免费看| av在线app专区| 七月丁香在线播放| 久久精品熟女亚洲av麻豆精品| 九色成人免费人妻av| 国产欧美日韩精品一区二区| av在线天堂中文字幕| 麻豆成人av视频| 视频中文字幕在线观看| h日本视频在线播放| 一级毛片我不卡| 熟女电影av网| 午夜爱爱视频在线播放| 国产精品国产三级专区第一集| 热re99久久精品国产66热6| 街头女战士在线观看网站| 干丝袜人妻中文字幕| av免费观看日本| 久久久久久久大尺度免费视频| 少妇人妻 视频| 极品少妇高潮喷水抽搐| 又粗又硬又长又爽又黄的视频| 成人午夜精彩视频在线观看| 99九九线精品视频在线观看视频| 国产一区二区三区综合在线观看 | 国产久久久一区二区三区| 七月丁香在线播放| 美女被艹到高潮喷水动态| 欧美少妇被猛烈插入视频| 亚洲国产精品999| 免费观看性生交大片5| 大香蕉久久网| 国产亚洲av嫩草精品影院| 国内精品美女久久久久久| 亚洲成人久久爱视频| 久久99精品国语久久久| 特大巨黑吊av在线直播| 最近最新中文字幕免费大全7| 国产色婷婷99| 欧美性猛交╳xxx乱大交人| 亚洲国产日韩一区二区| 一本久久精品| 国内少妇人妻偷人精品xxx网站| 人妻系列 视频| 日本午夜av视频| 伊人久久国产一区二区| 有码 亚洲区| 亚洲国产精品999| 69av精品久久久久久| 在线a可以看的网站| 国产老妇伦熟女老妇高清| 2022亚洲国产成人精品| 女的被弄到高潮叫床怎么办| 久久久久久伊人网av| 国产探花在线观看一区二区| 啦啦啦啦在线视频资源| 欧美bdsm另类| 成人美女网站在线观看视频| 精品一区在线观看国产| 精品酒店卫生间| 春色校园在线视频观看| 日韩一本色道免费dvd| 亚洲精品中文字幕在线视频 | 免费观看av网站的网址| 亚洲精品第二区| 美女主播在线视频| 亚洲人成网站高清观看| 青春草亚洲视频在线观看| 少妇高潮的动态图| 好男人在线观看高清免费视频| 日产精品乱码卡一卡2卡三| 亚洲精品国产av蜜桃| 免费不卡的大黄色大毛片视频在线观看| 99久久精品一区二区三区| 午夜亚洲福利在线播放| 国产有黄有色有爽视频| 秋霞在线观看毛片| 亚洲美女视频黄频| av专区在线播放| 视频中文字幕在线观看| 一级毛片黄色毛片免费观看视频| 少妇熟女欧美另类| 日本wwww免费看| 国产淫语在线视频| 欧美性感艳星| 精品国产露脸久久av麻豆| 亚洲人与动物交配视频| 久久久久精品久久久久真实原创| 国产免费又黄又爽又色| 午夜免费鲁丝| 亚洲电影在线观看av| 秋霞在线观看毛片| 亚洲怡红院男人天堂| 亚洲丝袜综合中文字幕| 午夜免费鲁丝| 亚洲第一区二区三区不卡| 久久精品夜色国产| 日韩不卡一区二区三区视频在线| 成年女人在线观看亚洲视频 | 欧美xxⅹ黑人| 久久精品久久久久久久性| 国产精品久久久久久精品电影| 男人添女人高潮全过程视频| 青青草视频在线视频观看| .国产精品久久| 亚洲成人久久爱视频| 日韩中字成人| 天堂网av新在线| 久久人人爽av亚洲精品天堂 | 黑人高潮一二区| kizo精华| 精品久久久精品久久久| av在线观看视频网站免费| 久久久久久久久久久丰满| 欧美国产精品一级二级三级 | 欧美人与善性xxx| 一本久久精品| 自拍偷自拍亚洲精品老妇| 97在线人人人人妻| 舔av片在线| 大陆偷拍与自拍| 国产美女午夜福利| 男女下面进入的视频免费午夜| 国产免费又黄又爽又色| 69人妻影院| 三级国产精品欧美在线观看| 晚上一个人看的免费电影| 777米奇影视久久| 十八禁网站网址无遮挡 | 丝袜美腿在线中文| 国产爱豆传媒在线观看| 内地一区二区视频在线| 精品久久久久久久久av| www.av在线官网国产| 在线免费十八禁| 在线观看一区二区三区| 亚洲av中文字字幕乱码综合| 色播亚洲综合网| 1000部很黄的大片| 中文字幕免费在线视频6| 国产男女内射视频| 国产毛片a区久久久久| 丝袜脚勾引网站| 日韩精品有码人妻一区| 久久久久久久亚洲中文字幕| 在线观看美女被高潮喷水网站| 国产av码专区亚洲av| 麻豆乱淫一区二区| 丰满人妻一区二区三区视频av| 国产毛片在线视频| 热99国产精品久久久久久7| 97人妻精品一区二区三区麻豆| 夜夜爽夜夜爽视频| 丝袜美腿在线中文| 亚洲精品自拍成人| 亚洲天堂国产精品一区在线| 在线观看国产h片| 一级毛片黄色毛片免费观看视频| 美女高潮的动态| 777米奇影视久久| 成人高潮视频无遮挡免费网站| av女优亚洲男人天堂| 日韩精品有码人妻一区| 国产成人午夜福利电影在线观看| 一区二区三区乱码不卡18| 国产极品天堂在线| 国产精品麻豆人妻色哟哟久久| 日本爱情动作片www.在线观看| 纵有疾风起免费观看全集完整版| 熟妇人妻不卡中文字幕| 噜噜噜噜噜久久久久久91| 国产精品久久久久久久电影| 91精品国产九色| 国产成人福利小说| 夫妻性生交免费视频一级片| 性色av一级| 自拍欧美九色日韩亚洲蝌蚪91 | 国产精品99久久久久久久久| 中文乱码字字幕精品一区二区三区| 少妇丰满av| 久久久欧美国产精品| 男插女下体视频免费在线播放| 免费观看a级毛片全部| 青春草视频在线免费观看| 91精品伊人久久大香线蕉| 亚洲精品乱码久久久久久按摩| 免费人成在线观看视频色| 超碰av人人做人人爽久久| 1000部很黄的大片| 蜜桃亚洲精品一区二区三区| 亚洲av.av天堂| 久久久精品免费免费高清| 男男h啪啪无遮挡| 欧美亚洲 丝袜 人妻 在线| 免费看av在线观看网站| 少妇人妻 视频| 精品一区二区三卡| 一个人观看的视频www高清免费观看| 亚洲激情五月婷婷啪啪| 国产色爽女视频免费观看| 久久97久久精品| 神马国产精品三级电影在线观看| 又黄又爽又刺激的免费视频.| 欧美zozozo另类| 蜜臀久久99精品久久宅男| 国产精品麻豆人妻色哟哟久久| 一二三四中文在线观看免费高清| 日日啪夜夜撸| 黄色欧美视频在线观看| 王馨瑶露胸无遮挡在线观看| 国产真实伦视频高清在线观看| 久久这里有精品视频免费| 插阴视频在线观看视频| 欧美日韩精品成人综合77777| 看黄色毛片网站| 亚洲精品国产av成人精品| 精品国产乱码久久久久久小说| 午夜视频国产福利| 2021少妇久久久久久久久久久|