Sugar Beet Cyst Nematode Heterodera Research Articles

Indigenous Populations of a Biological Control Agent in Agricultural Field Soils Predicted Suppression of a Plant Pathogen.

The nematophagous fungus Hyalorbilia oviparasitica and relatives (Hyalorbilia spp.) are known to parasitize several endoparasitic nematodes. In this project, we hypothesized that indigenous populations of this fungus could be used to predict nematode suppression in agricultural field soils. We quantified Hyalorbilia spp. in soil samples from 44 different sugar beet fields in the Imperial Valley of California. Seven soils harboring Hyalorbilia spp. and two that tested negative for the fungi were examined for nematode suppressive activity. Untreated and autoclaved portions of each soil were planted with cabbage and infested with sugar beet cyst nematode (Heterodera schachtii) juveniles. Females and cysts of H. schachtii were enumerated after 12 weeks. In the seven soils harboring Hyalorbilia spp., females and cysts in the untreated soils were reduced by 61 to 82% compared with the autoclaved controls. Soils with no detectable Hyalorbilia spp. exhibited no nematode suppression. Two novel Hyalorbilia strains, HsImV25 and HsImV27, were isolated from H. schachtii females reared in field soil using an enrichment and double-baiting cultivation technique. Both strains suppressed H. schachtii populations by more than 80% in soil-based assays, confirming that Hyalorbilia spp. are the likely causal agents of the nematode suppression in these soils. This study demonstrated that indigenous populations of a hyperparasite (Hyalorbilia spp.) in agricultural field soils predicted suppressive activity against a soilborne plant pathogen (H. schachtii). To our knowledge, this is the first report to demonstrate this capability. We anticipate that this research will provide a blueprint for other similar studies, thereby advancing the field of soilborne biological control.

Genome-wide identification and characterization of putative effectors in Heterodera schachtii that suppress plant immune response 1

The sugar beet cyst nematode (Heterodera schachtii) is one of the most destructive pathogens in sugar beet production, which causes serious economic losses every year. Few molecular details of effectors of H. schachtii parasitism are known. We analyzed the genome and transcriptome data of H. schachtii and identified multiple potential predicted proteins. After filtering out predicted proteins with high homology to other plant-parasitic nematodes, we performed functional validation of the remaining effector proteins. 37 putative effectors of H. schachtii were screened based on the Nicotiana benthamiana system for identifying the effectors that inhibit plant immune response, eventually determines 13 candidate effectors could inhibit cell death caused by Bax. Among the 13 effectors, nine have the ability to inhibit GPA2/RBP1-induced cell death. All 13 effector-triggered immunity (ETI) suppressor genes were analyzed by qRT-PCR and confirmed to result in a significant downregulation of one or more defense genes during infection compared to empty vector. For in situ hybridization, 13 effectors were specifically expressed and located in esophageal gland cells. These data and functional analysis set the stage for further studies on the interaction of H. schachtii with host and H. schachtii parasitic control.

A novel sugar beet cyst nematode effector 2D01 targets the Arabidopsis HAESA receptor-like kinase.

Plant-parasitic cyst nematodes use a stylet to deliver effector proteins produced in oesophageal gland cells into root cells to cause disease in plants. These effectors are deployed to modulate plant defence responses and developmental programmes for the formation of a specialized feeding site called a syncytium. The Hg2D01 effector gene, coding for a novel 185-amino-acid secreted protein, was previously shown to be up-regulated in the dorsal gland of parasitic juveniles of the soybean cyst nematode Heterodera glycines, but its function has remained unknown. Genome analyses revealed that Hg2D01 belongs to a highly diversified effector gene family in the genomes of H. glycines and the sugar beet cyst nematode Heterodera schachtii. For functional studies using the model Arabidopsis thaliana-H. schachtii pathosystem, we cloned the orthologous Hs2D01 sequence from H. schachtii. We demonstrate that Hs2D01 is a cytoplasmic effector that interacts with the intracellular kinase domain of HAESA (HAE), a cell surface-associated leucine-rich repeat (LRR) receptor-like kinase (RLK) involved in signalling the activation of cell wall-remodelling enzymes important for cell separation during abscission and lateral root emergence. Furthermore, we show that AtHAE is expressed in the syncytium and, therefore, could serve as a viable host target for Hs2D01. Infective juveniles effectively penetrated the roots of HAE and HAESA-LIKE2 (HSL2) double mutant plants; however, fewer nematodes developed on the roots, consistent with a role for this receptor family in nematode infection. Taken together, our results suggest that the Hs2D01-AtHAE interaction may play an important role in sugar beet cyst nematode parasitism.

Conserved Opposite Functions in Plant Resistance to Biotrophic and Necrotrophic Pathogens of the Immune Regulator SRFR1.

Plant immunity is mediated in large part by specific interactions between a host resistance protein and a pathogen effector protein, named effector-triggered immunity (ETI). ETI needs to be tightly controlled both positively and negatively to enable normal plant growth because constitutively activated defense responses are detrimental to the host. In previous work, we reported that mutations in SUPPRESSOR OF rps4-RLD1 (SRFR1), identified in a suppressor screen, reactivated EDS1-dependent ETI to Pseudomonas syringae pv. tomato (Pto) DC3000. Besides, mutations in SRFR1 boosted defense responses to the generalist chewing insect Spodoptera exigua and the sugar beet cyst nematode Heterodera schachtii. Here, we show that mutations in SRFR1 enhance susceptibility to the fungal necrotrophs Fusarium oxysporum f. sp. lycopersici (FOL) and Botrytis cinerea in Arabidopsis. To translate knowledge obtained in AtSRFR1 research to crops, we generated SlSRFR1 alleles in tomato using a CRISPR/Cas9 system. Interestingly, slsrfr1 mutants increased expression of SA-pathway defense genes and enhanced resistance to Pto DC3000. In contrast, slsrfr1 mutants elevated susceptibility to FOL. Together, these data suggest that SRFR1 is functionally conserved in both Arabidopsis and tomato and functions antagonistically as a negative regulator to (hemi-) biotrophic pathogens and a positive regulator to necrotrophic pathogens.

THE PROBLEM OF SUGAR BEET CYST NEMATODES IN MODERN CONDITIONS OF MACROECONOMIC AND CLIMATIC CHALLENGES

In this work, the current state of infection of the cultivated areas of sugar beet farms with the sugar beet cyst nematode Heterodera schachtii is considered. After the systemic crisis of agricultural production in the early 90th, the practice of operating Russian sugar factories not using domestic (sugar beet) but imported (cane) raw materials was widespread. For many years, in the absence of a host plant in the fields, the population density of highly specialized phytohelminths naturally decreased to an economically imperceptible level. However, in accordance with the principle of irreversibility of soil biocontamination of agroecosystems, the nematode retained its presence due to the mechanisms of mesobiosis and the maintenance of the population on reserve weeds. After the strategic course taken in 2014 towards import substitution, sugar beet areas (usually around sugar factories) returned to the main crop, and in 2018, for the first time in its history, Russia even became a sugar exporting country. However, the technological regulations of the USSR, mostly crop rotations were not observed and the nematode problem was again actualized, first of all, in the Chernozem and Krasnodar region. The proposed model of the dynamics of the population density of the nematodes, depending on the cultivated crop, makes it possible to assess the ecological and economic consequences of disturbed crop rotation, taking into account the conjuncture of the world food market. Climate change is another important challenge to be considered in the assessment of the nematode problem. Along with the noted increase in the bioclimatic potential of a number of agricultural lands in the Russian Federation, the development of the parasite during the growing season can occur not in three generations with a reduced fourth, but with a full cycle for the fourth generation.

Influence of sugar beet variety and initial population of sugar beet cyst nematode (Heterodera schachtii Schmidt) in soil on nematode development and sugar beet yield and root quality

W latach 2017–2018 przeprowadzono doświadczenia polowe, w których oceniano zmienność plonów oraz jakość technologiczną korzeni sześciu odmian buraka cukrowego tolerancyjnych na mątwika burakowego uprawianych w warunkach niskiej i wysokiej presji szkodnika na tle dwóch odmian standardowych. Zmiany zagęszczenia mątwika burakowego zależały istotnie od roku badań, zawartości szkodnika w glebie na początku wegetacji oraz odmiany buraka. Niezależnie od roku i populacji inicjalnej mątwika, odmiany tolerancyjne przyczyniały się do wzrostu zagęszczenia nicieni w mniejszym stopniu niż standardowe. W 2017 r. średni współczynnik P wyniósł odpowiednio 4,41 i 4,77, natomiast w 2018 r. 1,21 i 1,69. Odmiany buraka wykazały bardzo duże zróżnicowanie pod względem uzyskanych efektów produkcyjnych. Cecha tolerancji determinowała plon korzeni, zawartość cukru w korzeniach oraz plon cukru technologicznego w większym stopniu w 2018 r., w warunkach bardzo wysokiego początkowego zamątwiczenia (1556 larw i jaj na 100 g gleby). W 2017 r. w grupie odmian tolerancyjnych w porównaniu do standardowych stwierdzono wzrost plonu korzeni 17,1%, zawartości cukru w korzeniach 0,25 punktu procentowego oraz plonu cukru technologicznego 18,0%, natomiast w 2018 r. odpowiednio 89,2%, 2,13 punktu procentowego i 114,1%. In 2017–2018, field experiments were carried out in which the variability of yields and the technological quality of roots of six sugar beet cultivars tolerant to beet nematode cultivated under low and high pest pressure conditions were assessed against the background of two standard cultivars. Changes in the nematode density significantly depended on the year of the study, pest content at the season beginning and the beet variety. Regardless of the year and the initial nematode population, tolerant cultivars contributed to increase nematode population less than the standard ones. In 2017, the average P factor was 4.41 and 4.77 respectively, while in 2018 it was 1.21 and 1.69. The tested cultivars showed a very large diversity in obtained production effects. The feature of tolerance determined root yield, sugar content in roots and technological sugar yield to a greater extent in 2018 under conditions of very high initial population (1556 larvae and eggs per 100 g soil). In 2017 in the group of tolerant varieties compared to standard varieties an increase in root yield 17.1%, sugar content in roots 0.25 percentage point and technological sugar yield 18.0% was observed, while in 2018, respectively 89.2%, 2.13 percentage point and 114.1%.

Ascorbate Oxidase Induces Systemic Resistance in Sugar Beet Against Cyst Nematode Heterodera schachtii.

Ascorbate oxidase (AO) is an enzyme involved in catalyzing the oxidation of apoplastic ascorbic acid (AA) to dehydroascorbic acid (DHA). In this research, the potential of AO spraying to induce systemic resistance was demonstrated in the interaction between sugar beet root and cyst nematode Heterodera schachtii and the mechanism was elucidated. Plant bioassays showed that roots of AO-sprayed plants were infested by a significantly lower number of females and cysts when compared with mock-sprayed control plants. Hormone measurements showed an elevated level of jasmonic acid (JA) salicylic acid (SA) and ethylene (ET) in the roots of AO-sprayed plants, with a dynamic temporal pattern of activation. Experiments with chemical inhibitors showed that AO-induced systemic resistance is partially dependent on the JA, ET and SA pathways. Biochemical analyses revealed a primed accumulation of hydrogen peroxide (H2O2), and phenylalanine ammonia lyase (PAL) activity in the roots of AO-sprayed plants upon infection by cyst nematodes. In conclusion, our data shows that AO works as an effective systemic defense priming agent in sugar beet against cyst nematode infection, through activation of multiple basal plant defense pathways.

Analysis of molecular characterizations of beets, Beta vulgaris in response to cyst nematodes, Heterodera schachtii

Sugar beet cyst nematode Heterodera schachtii is a serious biotic limiting factor in sugar beet industry. In this study, 70 sugar beet accessions were screened against H. schachtii, of which 30 resistant and susceptible ones were subjected to polymorphic simple sequence repeat (SSR) marker analysis by seven Universal DNA Amplification (UDA) primer pairs randomly. The results showed a very high significant variation between resistant and susceptible sugar beet accessions in response to H. schachtii with 42 fold increase in nematode reproduction rate in susceptible ones. SSR primers produced 155 bands, out of which 91 ones showed polymorphism, indicating 59% genetic diversity. The highest polymorphic bands was of UDA013 primer with 17 and the lowest one in UDA010 with 10 bands. Average number of polymorphic bands per primer was 13 and per genotype 3.03 bands. The UDA015 had the highest polymorphic index content (PIC) of 80%, and the lowest 44% in UDA001 with the mean of 67%. Highest marker index (MI) was in UDA015 with 10.80, and lowest one 6.48 in UDA001, with the mean of 8.68. Cluster analysis using Numerical Taxonomy and Multivariate Analysis System (NTSYS) software, with UPGMA method based on Jacard's similarity matrix, divided the genotypes into 4 major clusters. The dendrogram was consistent with the clustering result of Principal Component Analysis (PCoA). The highest genetic similarity of 91% was between the genotypes 45 and 51, of which both were offspring of a half-brother and half-sister crossing. The results suggested novel sources of resistant to H. schachtii and that SSR marker is a reliable tool for revealing a high levels of polymorphism among the sugar beet genotypes.

Re-targeting of a plant defense protease by a cyst nematode effector.

Plants mount defense responses during pathogen attacks, and robust host defense suppression by pathogen effector proteins is essential for infection success. 4E02 is an effector of the sugar beet cyst nematode Heterodera schachtii. Arabidopsis thaliana lines expressing the effector-coding sequence showed altered expression levels of defense response genes, as well as higher susceptibility to both the biotroph H. schachtii and the necrotroph Botrytis cinerea, indicating a potential suppression of defenses by 4E02. Yeast two-hybrid analyses showed that 4E02 targets A. thaliana vacuolar papain-like cysteine protease (PLCP) 'Responsive to Dehydration 21A' (RD21A), which has been shown to function in the plant defense response. Activity-based protein profiling analyses documented that the in planta presence of 4E02 does not impede enzymatic activity of RD21A. Instead, 4E02 mediates a re-localization of this protease from the vacuole to the nucleus and cytoplasm, which is likely to prevent the protease from performing its defense function and at the same time, brings it in contact with novel substrates. Yeast two-hybrid analyses showed that RD21A interacts with multiple host proteins including enzymes involved in defense responses as well as carbohydrate metabolism. In support of a role in carbohydrate metabolism of RD21A after its effector-mediated re-localization, we observed cell wall compositional changes in 4E02 expressing A. thaliana lines. Collectively, our study shows that 4E02 removes RD21A from its defense-inducing pathway and repurposes this enzyme by targeting the active protease to different cell compartments.

Development of a decision support system for managing Heterodera schahtii in sugar beet production.

Abstract A decision support system, SBN-Watch, was developed to demonstrate the influence of crop rotation and the choice of sugar beets (Beta vulgaris) varieties on the sugar beet cyst nematode Heterodera schachtii Schmidt (SBN) population and sugar beets yield. The database in SBN-Watch consists of a varietal unit with five sugar beet varieties representing the three categories “Standard,” “Tolerant” and “semi-tolerant.” Data of minimal yield (m), tolerance limit (T), and population dynamic parameters were obtained from published commercial field trials conducted in Sweden and Denmark in 2011. Additionally, a sanitation intercrop unit with different resistant classes of white mustard (Sinapsis arvensis) and oil seed radish (Raphanus sativus) was included. The relationship between initial population (Pi) and sugar yield as well as SBN final population in soil (Pf) was calculated by two Seinhorst equations. Few data inputs are required to be entered by the user in SBN-Watch, mainly the initial population (Pi), expected sugar price and exchange rate of € to SEK. The calculated reproduction factor (Rf) values using SBN-Watch corresponded well with varietal characteristics, where the standard variety Mixer had the highest (Rf) values. The influence of the initial SBN population on the calculated sugar yield (tonnes ha−1) was generally small at Pi < 2.

An Effector from the Cyst Nematode Heterodera schachtii Derepresses Host rRNA Genes by Altering Histone Acetylation.

Cyst nematodes are plant-pathogenic animals that secrete effector proteins into plant root cells to alter host gene expression and reprogram these cells to form specialized feeding sites, known as syncytia. The molecular mechanisms of these effectors are mostly unknown. We determined that the sugar beet cyst nematode (Heterodera schachtii) 32E03 effector protein strongly inhibits the activities of Arabidopsis thaliana histone deacetylases including the HDT1 enzyme, which has a known function in the regulation of rRNA gene expression through chromatin modifications. We determined that plants expressing the 32E03 coding sequence exhibited increased acetylation of histone H3 along the rDNA chromatin. At low 32E03 expression levels, these chromatin changes triggered the derepression of a subset of rRNA genes, which were conducive to H. schachtii parasitism. By contrast, high levels of 32E03 caused profound bidirectional transcription along the rDNA, which triggered rDNA-specific small RNA production leading to RNA-directed DNA methylation and silencing of rDNA, which inhibited nematode development. Our data show that the 32E03 effector alters plant rRNA gene expression by modulating rDNA chromatin in a dose-dependent manner. Thus, the 32E03 effector epigenetically regulates plant gene expression to promote cyst nematode parasitism.

Ethylene response pathway modulates attractiveness of plant roots to soybean cyst nematode Heterodera glycines

Plant parasitic nematodes respond to root exudates to locate their host roots. In our studies second stage juveniles of Heterodera glycines, the soybean cyst nematode (SCN), quickly migrated to soybean roots in Pluronic F-127 gel. Roots of soybean and non-host Arabidopsis treated with the ethylene (ET)-synthesis inhibitor aminoethoxyvinylglycine (AVG) were more attractive to SCN than untreated roots, and significantly more nematodes penetrated into roots. Moreover, Arabidopsis ET insensitive mutants (ein2, ein2-1, ein2-5, ein3-1, ein5-1, and ein6) were more attractive than wild-type plants. Conversely, the constitutive triple-response mutant ctr1-1, was less attractive to SCN. While ET receptor gain-of-function mutant ein4-1 attracted more SCN than the wild-type, there were no significant differences in attractiveness between another gain-of-function ET receptor mutant, etr1-3, or the loss-of-function mutants etr1-7 and ers1-3 and the wild type. Expression of the reporter construct EBS: β-glucuronidase (GUS) was detected in Arabidopsis root tips as early as 6 h post infection, indicating that ET signaling was activated in Arabidopsis early by SCN infection. These results suggest that an active ET signaling pathway reduces root attractiveness to SCN in a way similar to that reported for root-knot nematodes, but opposite to that suggested for the sugar beet cyst nematode Heterodera schachtii.

Sugar beet nematode Heterodera schachtii distribution and harmfulness in Ukraine

Aim. To determine the distribution of sugar beet cyst nematode Heterodera schachtii in Ukraine, to defi ne its population density in soil, the degree of damage and the effi ciency of control measures. Methods. Field survey for soil samples, cyst extraction by fl otation and sieving method, light microscopy. Results. The examination of 12,130 ha of agricultural fi elds in six regions of Ukraine, conducted in 2010–2015, recorded the sugar beet cyst nematode to occur in fi ve of them (Kyiv, Chernihiv, Cherkasy, Khmelnytsky, and Vinnytsia), at a total area of 2,572 ha. Taking into consideration the results of previous nematological surveys, the presence of sugar beet cyst nematode has now been documented for 18 regions of Ukraine. In most regions H. schachtii was present in 10–11 % of the examined sugar and seed producing farms with nematode population densities reaching up to 142,000 eggs and juveniles in 100 cc of soil (710-fold above the economic threshold). Conclusions. The main reasons for this wide distribution of H. schachtii in Ukraine are seen in the negligence of prevention measures, unavailability of documented data on its occurrence (missing surveys), crop rotations with over 20 % of host plants, and unavailability of effi cient nematicides and domestic nematode-resistant sugar beet cultivars.

Dispersal of sugar beet cyst nematode (Heterodera schachtii) by water and soil in highland Chinese cabbage fields

사탕무씨스트선충(Heterodera schachtii)은 전세계적으로 십자화과 작물에 심각한 경제적 손실을 유발시키는 선충으로 2011년 우리나라의 고랭지 채소 재배지에 최초 발생이 확인되었다. 고랭지 배추 재배지에 사탕무씨스트선충에 의한 피해가 증 가하고 있는 실정이나 피해 확산에 대한 실제적 원인 규명이 없어 본 연구에서는 고랭지 배추 재배지에서 작업화와 작업차량, 물을 통한 사탕무씨스트선충의 확산 가능성을 구명하기 위하여 수행하였다. 사탕무씨스트 선충 감염지에서 작업 할 경우 신발 에 묻은 흙에 사탕무씨스트선충이 존재하였는데 부착 된 씨스트선충의 수는 지역별로 차이가 있었다. 사탕무씨스트선충에 감염된 배추 밭 농로를 주행 한 차량의 바퀴에서도 사탕무씨스트 선충의 부착이 확인 되었다. 고랭지 배추 재배지에서 배추 수확 시 사용하는 굴삭기의 궤도에서는 41kg의 흙이 부착되었으며 장거리 수송용 5톤 트럭의 바퀴 네 개에서도 223.7g의 흙이 채취 되어 수확 작업 시 다량의 사탕무시스트선충이 부착될 수 있음을 확인 할 수 있었다. 강우 시 사탕무씨스트선충 감염 포장에서 작업할 경우를 가정하여 관주량별(2, 4, 8Lㆍm-2)에 따른 작업화 부착 흙 양과 사탕무씨스트선충 부착량을 조사한 결과 관주량 이 많을수록 장화에 부착되는 흙의 양은 많았으나 사탕무씨스트선충의 밀도는 차이가 없었다. 강우 시, 사탕무시스트선충 감 염지에서는 유거수를 통해 사탕무씨스트 선충이 이동하였다. 우리나라 고랭지 배추 재배지에서 신규 도입 선충인 사탕무씨스 트선충은 작업자의 작업화와 수확 작업에 이용되는 굴삭기와 차량의 바퀴 및 물을 통해 확산이 이루어 질 수 있음을 구명하였 다. 따라서 사탕무씨스트선충 감염지역에서는 작업자의 개인 위생과 작업 차량에 대한 토양 제거를 통해 감염 확산을 막아야 할 것으로 판단된다.

Gene Expression Analysis of Jasmonic Acid Related Genes during Root Infection of a Sugarbeet Cyst Nematode (Heterodera schachtii) on the Arabidopsis thaliana Plant

In several plant species, the establishment of systemically acquired resistance is associated with enhanced transcription of a large number of genes. This study aimed to analyze the expression of Jasmonic Acid (JA) related genes (COI 1, JAR 1, PDF 1.2A) in roots and shoots during cyst nematode infection on the Arabidopsis thaliana roots. The gene expression analysis results showed that while PDF1.2A was down-regulated in the roots, the reverse occurred in the leaf samples 24 hours after the sugarbeet cyst nematode inoculation. This indicates that the shoot defense system was activated during nematode root infection, thus, there is a systemic acquired resistance occurring in the shoots.

Integrated control of Heterodera schachtii Schmidt in Central Europe by trap crop cultivation, sugar beet variety choice and nematicide application

An integrated strategy is required to control the sugar beet cyst nematode Heterodera schachtii which causes severe yield losses in sugar beet. This study aimed at evaluating the effect of trap crop cultivation (nematode resistant mustard, crop mixture (Trifolium alexandrinum L., Lupinus angustifolius L., Pisum sativum L., Phacelia tanacetifolia Benth., Guizotia abyssinica (L.F.) Cass., Avena strigosa Schreb., Vicia sativa L.), straw mulch as control), nematicide application before sugar beet sowing and sugar beet variety (susceptible, tolerant or resistant to H. schachtii) on population dynamics of H. schachtii and sugar yield. Field experiments were conducted in eight environments (site×year) located in Northern Germany in 2012–2013 and 2013–2014. An insufficient trap crop dry matter yield (1.1–2.5tha−1) mostly led to non-significant trap crop effects on the nematode population whereas in one environment a high dry matter yield of mustard (3.3tha−1) resulted in a nematode reduction of 40%. However, there were no significant differences to the straw mulch control. The nematicide application had no effect on nematode reproduction. In contrast, population dynamics of H. schachtii were strongly influenced by the sugar beet variety and the initial nematode population (PiSB). The highest reduction of 70% was achieved when a resistant sugar beet variety was grown, while the tolerant and susceptible varieties increased the nematode population in most environments. There was evidence that the sugar beet harvest date can highly influence population dynamics of H. schachtii. Sugar yield was influenced by variety and PiSB, but not by trap crop cultivation or nematicide application. Sugar yield decreased with increasing PiSB for all varieties. The resistant and tolerant varieties did not differ in sugar yield and response to H. schachtii, while the susceptible showed the steepest decline in sugar yield with increasing PiSB. The cultivation of the resistant sugar beet variety can be clearly suggested with respect to sugar yield and nematode control because all other tested factors failed to control the nematode population.

Interspecific and host-related gene expression patterns in nematode-trapping fungi.

BackgroundNematode-trapping fungi are soil-living fungi that capture and kill nematodes using special hyphal structures called traps. They display a large diversity of trapping mechanisms and differ in their host preferences. To provide insights into the genetic basis for this variation, we compared the transcriptome expressed by three species of nematode-trapping fungi (Arthrobotrys oligospora, Monacrosporium cionopagum and Arthrobotrys dactyloides, which use adhesive nets, adhesive branches or constricting rings, respectively, to trap nematodes) during infection of two different plant-pathogenic nematode hosts (the root knot nematode Meloidogyne hapla and the sugar beet cyst nematode Heterodera schachtii).ResultsThe divergence in gene expression between the fungi was significantly larger than that related to the nematode species being infected. Transcripts predicted to encode secreted proteins and proteins with unknown function (orphans) were overrepresented among the highly expressed transcripts in all fungi. Genes that were highly expressed in all fungi encoded endopeptidases, such as subtilisins and aspartic proteases; cell-surface proteins containing the carbohydrate-binding domain WSC; stress response proteins; membrane transporters; transcription factors; and transcripts containing the Ricin-B lectin domain. Differentially expressed transcripts among the fungal species encoded various lectins, such as the fungal fruit-body lectin and the D-mannose binding lectin; transcription factors; cell-signaling components; proteins containing a WSC domain; and proteins containing a DUF3129 domain. A small set of transcripts were differentially expressed in infections of different host nematodes, including peptidases, WSC domain proteins, tyrosinases, and small secreted proteins with unknown function.ConclusionsThis is the first study on the variation of infection-related gene expression patterns in nematode-trapping fungi infecting different host species. A better understanding of these patterns will facilitate the improvements of these fungi in biological control programs, by providing molecular markers for screening programs and candidates for genetic manipulations of virulence and host preferences.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-968) contains supplementary material, which is available to authorized users.

Occurrence of Heterodera schachtii in the sugar beet growing areas of Vojvodina, Serbia

The survey on the occurrence of the sugar beet cyst nematode Heterodera schachtii Schmidt 1871 was performed from November 2006 until June 2012 in the sugar beet growing areas of the Serbian northern Province of Vojvodina. The soil samples were taken from 55 beet fields and analyzed for number of viable eggs or juveniles in the soil. In total, 1387 soil samples were collected from 20 sugar beet producers and 3 seed fodder beet producers. Fenwick can and electric device for crushing cysts were used in order to determine the presence of cysts and population density. Heterodera schachtii occurred in 36.36 % of beet fields with population density ranging from 13 to 1591 eggs and second-stage juveniles in 100 cm3 of soil. The area with the most infected fields was the district of Backa. Only in the district of Banat H. schachtii was not detected. Current occurrence of H. schachtii in the sugar beet growing areas of Vojvodina indicates that this pest is most frequently found near old sugar beet factories in the districts of Backa and Srem as a result of intensive sugar beet cultivation with narrow crop rotation.

Dactylella oviparasitica parasitism of the sugar beet cyst nematode observed in trixenic culture plates

The nematophagous fungus Dactylella oviparasitica is considered the primary cause of a sugar beet cyst nematode (Heterodera schachtii) population suppression in a field at the Agricultural Operations, University of California, Riverside. Parasitism of H. schachtii by the ascomycete D. oviparasitica was studied using both Arabidopsis thaliana (type Landsberg erecta) and cabbage as host plants in gnotobiotic agar culture. Suitability of Arabidopsis as a host for H. schachtii was confirmed using seedlings grown with the nematode in axenic sand culture. Both developing males and females of H. schachtii broke through the Arabidopsis root surface during late juvenile stages and both were susceptible to D. oviparasitica parasitism. In contrast to Arabidopsis, developing juvenile males remained in nearly all observed cases enclosed within the cabbage root tissues while the larger body expansion of the female juveniles caused the root cortex to split; consequently only the latter ones were accessible to the fungus. In the presence of D. oviparasitica, the number of females with eggs was reduced by more than 95% and the number of eggs per female by almost 60% as compared to females developing on plates without the fungus. Viable eggs were not susceptible to parasitism while more than 90% of heat- or cold-killed eggs were rendered susceptible. These observations suggest that parasitism of developing juveniles may be the essential mode of action in the population suppression of H. schachtii.

The Arabidopsis bHLH25 and bHLH27 transcription factors contribute to susceptibility to the cyst nematode Heterodera schachtii

Successful cyst nematode parasitism depends on the formation and maintenance of feeding sites (syncytia) in host roots, and these processes are highly regulated by the interaction between the cyst nematode and the host. Using an integrated research approach and the Arabidopsis-Beta vulgaris (sugar beet) cyst nematode (Heterodera schachtii) pathosystem, we have determined that the two Arabidopsis basic helix-loop-helix transcription factors bHLH25 and bHLH27 positively influence cyst nematode parasitism. Promoter studies indicated that as early as 1 day post-inoculation, both transcription factor genes were upregulated in developing syncytia, whereas in non-infected plants, these two promoters were not found to be active in the same cells. By using yeast two-hybrid analyses and bimolecular fluorescence complementation assays, we documented that the two bHLH transcription factors can dimerize in planta. Transgenic Arabidopsis plants overexpressing either one or both of the bHLH genes exhibited altered morphology of roots and shoots, as well as an increased susceptibility to H. schachtii. bhlh25 or bhlh27 single mutants were without strong phenotypes, presumably because of functional redundancies in this gene family. However, the bhlh25 bhlh27 double mutant was less susceptible to H. schachtii, confirming an important conducive role of the co-expression of both transcription factor genes for cyst nematode parasitism. Our results document an example of pathogen-induced ectopic co-expression of two regulatory genes to enhance pathogen success, although these transcription factors apparently do not function in concert in non-infected plants. This is an intriguing biological phenomenon that highlights the complexity of obligate biotrophic plant-pathogen interactions, like those of cyst nematodes.