Beet Cyst Nematode Heterodera Schachtii Research Articles

Transcription factor WOX11 modulates tolerance to cyst nematodes via adventitious lateral root formation.

The transcription factor WUSCHEL-RELATED HOMEOBOX 11 (WOX11) in Arabidopsis (Arabidopsis thaliana) initiates the formation of adventitious lateral roots upon mechanical injury in primary roots. Root-invading nematodes also induce de novo root organogenesis leading to excessive root branching, but it is not known if this symptom of disease involves mediation by WOX11 and if it benefits the plant. Here, we show with targeted transcriptional repression and reporter gene analyses in Arabidopsis that the beet cyst nematode Heterodera schachtii activates WOX11-mediated adventitious lateral rooting from primary roots close to infection sites. The activation of WOX11 in nematode-infected roots occurs downstream of jasmonic acid-dependent damage signaling via ETHYLENE RESPONSE FACTOR109, linking adventitious lateral root formation to nematode damage to host tissues. By measuring different root system components, we found that WOX11-mediated formation of adventitious lateral roots compensates for nematode-induced inhibition of primary root growth. Our observations further demonstrate that WOX11-mediated rooting reduces the impact of nematode infections on aboveground plant development and growth. Altogether, we conclude that the transcriptional regulation by WOX11 modulates root system plasticity under biotic stress, which is one of the key mechanisms underlying the tolerance of Arabidopsis to cyst nematode infections.

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.

Genetic Variation among Heterodera schachtii Populations Coincided with Differences in Invasion and Propagation in Roots of a Set of Cruciferous Plants.

Genes of host plants and parasitic nematodes govern the plant-nematode interaction. The biological receptors and parasitism effectors are variable among plant species and nematode populations, respectively. In the present study, hatch testing and bioassays on cabbage, oilseed radish, and mustard were conducted to compare the biological characteristics among six populations of the beet cyst nematode Heterodera schachtii. Genetic patterns of the vap1 gene for the studied populations were distinct as shown by denaturing the gradient gel electrophoresis of PCR-amplified gene fragments. Concurrently, significant differences in the hatching rates, number of penetrated J2 in roots, and eggs/cyst ratios among the six nematode populations for the three cruciferous species were observed. In conclusion, analyzing the population genetic structure of H. schachtii plays a pivotal role in illustrating the variability in the plant-nematode interaction among its populations and plant species, which in its role leads to developing nematode management depending on plant resistance.

Volatile Organic Compounds from a Lichen-Associated Bacterium, Paenibacillus etheri, Interact with Plant-Parasitic Cyst Nematodes.

Healthy food is one of the major challenges to develop in this century. Plant-parasitic nematodes cause significant damage to many crops worldwide and till now, the use of chemical nematicides is the main means to control their populations. These chemical products must be replaced by more environmental-friendly control methods. Biocontrol methods seem to be one promising option, and the number of biopesticides derived from living organisms has increased in the last decades. To develop new plant protection products, we have decided to combine our skills in natural products chemistry and nematology and to focus on the lichen microecosystem as underexploited ecological niches of microorganisms. We present herein the potential of lichen-associated bacterial suspensions from Paenibacillus etheri as nematicides against the beet cyst nematode Heterodera schachtii and the potato cyst nematode Globodera pallida, in particular the effects of volatile organic compounds (VOCs) produced by the bacteria. A solid phase micro-extraction method associated to gas chromatography-mass spectrometry analysis of 14 day cultures was used to analyze these VOCs in order to identify the main produced compounds (isoamyl acetate and 2-phenylethyl acetate) and to evaluate them on the nematodes.

High-throughput phenotyping of nematode cysts.

The beet cyst nematode Heterodera schachtii is a plant pest responsible for crop loss on a global scale. Here, we introduce a high-throughput system based on computer vision that allows quantifying beet cyst nematode infestation and measuring phenotypic traits of cysts. After recording microscopic images of soil sample extracts in a standardized setting, an instance segmentation algorithm serves to detect nematode cysts in these images. In an evaluation using both ground truth samples with known cyst numbers and manually annotated images, the computer vision approach produced accurate nematode cyst counts, as well as accurate cyst segmentations. Based on such segmentations, cyst features could be computed that served to reveal phenotypical differences between nematode populations in different soils and in populations observed before and after the sugar beet planting period. The computer vision approach enables not only fast and precise cyst counting, but also phenotyping of cyst features under different conditions, providing the basis for high-throughput applications in agriculture and plant breeding research. Source code and annotated image data sets are freely available for scientific use.

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.

Comparative genomics among cyst nematodes reveals distinct evolutionary histories among effector families and an irregular distribution of effector-associated promoter motifs.

Potato cyst nematodes (PCNs), an umbrella term used for two species, Globodera pallida and G. rostochiensis, belong worldwide to the most harmful pathogens of potato. Pathotype-specific host plant resistances are essential for PCN control. However, the poor delineation of G. pallida pathotypes has hampered the efficient use of available host plant resistances. Long-read sequencing technology allowed us to generate a new reference genome of G. pallida population D383 and, as compared to the current reference, the new genome assembly is 42 times less fragmented. For comparison of diversification patterns of six effector families between G. pallida and G. rostochiensis, an additional reference genome was generated for an outgroup, the beet cyst nematode Heterodera schachtii (IRS population). Large evolutionary contrasts in effector family topologies were observed. While VAPs (venom allergen-like proteins) diversified before the split between the three cyst nematode species, the families GLAND5 and GLAND13 only expanded in PCNs after their separation from the genus Heterodera. Although DNA motifs in the promoter regions thought to be involved in the orchestration of effector expression ("DOG boxes") were present in all three cyst nematode species, their presence is not a necessity for dorsal gland-produced effectors. Notably, DOG box dosage was only loosely correlated with the expression level of individual effector variants. Comparison of the G. pallida genome with those of two other cyst nematodes underlined the fundamental differences in evolutionary history between effector families. Resequencing of PCN populations with different virulence characteristics will allow for the linking of these characteristics to the composition of the effector repertoire as well as for the mapping of PCN diversification patterns resulting from extreme anthropogenic range expansion.

MiR778 mediates gene expression, histone modification, and DNA methylation during cyst nematode parasitism.

Despite the known critical regulatory functions of microRNAs, histone modifications, and DNA methylation in reprograming plant epigenomes in response to pathogen infection, the molecular mechanisms underlying the tight coordination of these components remain poorly understood. Here, we show how Arabidopsis (Arabidopsis thaliana) miR778 coordinately modulates the root transcriptome, histone methylation, and DNA methylation via post-transcriptional regulation of the H3K9 methyltransferases SU(var)3-9 homolog 5 (SUVH5) and SUVH6 upon infection by the beet cyst nematode Heterodera schachtii. miR778 post-transcriptionally silences SUVH5 and SUVH6 upon nematode infection. Manipulation of the expression of miR778 and its two target genes significantly altered plant susceptibility to H. schachtii. RNA-seq analysis revealed a key role of SUVH5 and SUVH6 in reprograming the transcriptome of Arabidopsis roots upon H. schachtii infection. In addition, chromatin immunoprecipitation (ChIP)-seq analysis established SUVH5 and SUVH6 as the main enzymes mediating H3K9me2 deposition in Arabidopsis roots in response to nematode infection. ChIP-seq analysis also showed that these methyltransferases possess distinct DNA binding preferences in that they are targeting transposable elements under noninfected conditions and protein-coding genes in infected plants. Further analyses indicated that H3K9me2 deposition directed by SUVH5 and SUVH6 contributes to gene expression changes both in roots and in nematode feeding sites and preferentially associates with CG DNA methylation. Together, our results uncovered multi-layered epigenetic regulatory mechanisms coordinated by miR778 during Arabidopsis-H. schachtii interactions.

Arabidopsis thaliana AtHRS1 gene is involved in the response to Heterodera schachtii infection and its overexpression hampers development of syncytia and involves a jasmonic acid-dependent mechanism

Sedentary plant parasitic nematodes have developed competences to reprogram host plant cell metabolism via sophisticated manipulation of gene expression, leading to the formation of permanent feeding sites for an unlimited source of food. Arabidopsis thaliana and the beet cyst nematode Heterodera schachtii is a good model for studying the mechanisms of compatible plant-nematode interactions and basic plant responses to nematode infection. Transcription factors are proteins that modulate plant reactions during regular development and under different biotic and abiotic stresses via direct binding to promoter regions of genes. Here, we report on the AtHRS1 gene encoding a MYB-related transcription factor belonging to the GARP family, whose expression is downregulated in syncytia, as confirmed by gene expression analysis. Constitutive overexpression of AtHRS1 disturbed the development of nematode-induced syncytia and led to a reduction in the number of developed females in transgenic A. thaliana roots. In contrast, the hrs1 mutant with decreased expression of AtHRS1 was more susceptible to cyst nematode infection. The influence of AtHRS1 on selected elements of the JA-dependent defence pathway suggests its mode of action in plant response to nematode attack. Based on these results, we suggest that the downregulation of AtHRS1 expression by nematode is important for its successful development.

Characterization of an Arabidopsis Defensin-like Gene Conferring Resistance against Nematodes.

Arabidopsis contains 317 genes for defensin-like (DEFL) peptides. DEFLs have been grouped into different families based mainly on cysteine motifs. The DEFL0770 group contains seven genes, of which four are strongly expressed in roots. We found that the expression of these genes is downregulated in syncytia induced by the beet cyst nematode Heterodera schachtii as revealed by RNAseq analysis. We have studied one gene of this group, At3g59930, in detail. A promoter::GUS line revealed that the gene is only expressed in roots but not in other plant organs. Infection of the GUS line with larvae of H. schachtii showed a strong downregulation of GUS expression in infection sites as early as 1 dpi, confirming the RNAseq data. The At3g59930 peptide had only weak antimicrobial activity against Botrytis cinerea. Overexpression lines had no enhanced resistance against this fungus but were more resistant to H. schachtii infection. Our data indicate that At3g59930 is involved in resistance to nematodes which is probably not due to direct nematicidal activity.

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%.

The Plant Sesquiterpene Nootkatone Efficiently Reduces Heterodera schachtii Parasitism by Activating Plant Defense.

Plant parasitic nematodes, including the beet cyst nematode Heterodera schachtii, constitute a devastating problem for crops worldwide. The limited availability of sustainable management options illustrates the need for new eco-friendly control means. Plant metabolites represent an invaluable source of active compounds for the discovery of such novel antagonistic agents. Here, we evaluated the impact of eight plant terpenoids on the H. schachtii parasitism of Arabidopsis thaliana. None of the metabolites affected the plant development (5 or 10 ppm). Nootkatone decreased the number of adult nematodes on A. thaliana to 50%, with the female nematodes being smaller compared to the control. In contrast, three other terpenoids increased the parasitism and/or female size. We discovered that nootkatone considerably decreased the number of nematodes that penetrated A. thaliana roots, but neither affected the nematode viability or attraction to plant roots, nor triggered the production of plant reactive oxygen species or changed the plant’s sesquiterpene profile. However, we demonstrated that nootkatone led to a significant upregulation of defense-related genes involved in salicylic and jasmonic acid pathways. Our results indicate that nootkatone is a promising candidate to be developed into a novel plant protection agent acting as a stimulator of plant immunity against parasitic nematodes.

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.

Cyst Nematode Infection Elicits Alteration in the Level of Reactive Nitrogen Species, Protein S-Nitrosylation and Nitration, and Nitrosoglutathione Reductase in Arabidopsis thaliana Roots.

Reactive nitrogen species (RNS) are redox molecules important for plant defense against pathogens. The aim of the study was to determine whether the infection by the beet cyst nematode Heterodera schachtii disrupts RNS balance in Arabidopsis thaliana roots. For this purpose, measurements of nitric oxide (NO), peroxynitrite (ONOO−), protein S-nitrosylation and nitration, and nitrosoglutathione reductase (GSNOR) in A. thaliana roots from 1 day to 15 days post-inoculation (dpi) were performed. The cyst nematode infection caused generation of NO and ONOO− in the infected roots. These changes were accompanied by an expansion of S-nitrosylated and nitrated proteins. The enzyme activity of GSNOR was decreased at 3 and 15 dpi and increased at 7 dpi in infected roots, whereas the GSNOR1 transcript level was enhanced over the entire examination period. The protein content of GSNOR was increased in infected roots at 3 dpi and 7 dpi, but at 15 dpi, did not differ between uninfected and infected roots. The protein of GSNOR was detected in plastids, mitochondria, cytoplasm, as well as endoplasmic reticulum and cytoplasmic membranes. We postulate that RNS metabolism plays an important role in plant defense against the beet cyst nematode and helps the fine-tuning of the infected plants to stress sparked by phytoparasitic nematodes.

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.

Fungi isolated from cysts of the beet cyst nematode parasitized its eggs and counterbalanced root damages

Finding beneficial fungi antagonistic toward nematodes is important for developing more sustainable agricultural practices. We isolated abundant fungi from cysts of the beet cyst nematode Heterodera schachtii and tested their interaction with nematodes and sugar beet. By molecular screening of fungal communities colonizing five field populations of H. schachtii using DGGE and Sanger sequencing, three strains identified as Exophiala sp., Pochonia chlamydosporia and Pyrenochaeta sp. were frequently found in infected cysts and then specifically isolated (in pure culture). The three isolates were able to re-infect the cysts and colonize the eggs of H. schachtii in vitro fulfilling Koch’s postulates. In greenhouse trials, the root weight of sugar beet plants grown in substrates inoculated with nematodes and the fungal isolates was significantly higher compared to plants inoculated with nematodes only. The number of cysts propagated on roots was lower in substrates inoculated with Pyrenochaeta sp. than those in substrates inoculated with the other two fungi. However, cyst numbers did not significantly differ from the control because the propagation rate of the nematode increased with the root weight. The proportion of infected eggs per cyst was higher under the fungal treatments than the control, and it increased with the number of propagated cysts. The results showed that the here-studied strains of Exophiala sp., Pochonia chlamydosporia and Pyrenochaeta sp. were frequently found colonizing the nematode cysts of different populations of H. schachtii and were efficient in parasitizing the eggs of the nematode.

The Arabidopsis GPI-Anchored LTPg5 Encoded by At3g22600 Has a Role in Resistance against a Diverse Range of Pathogens.

Arabidopsis contains 34 genes for glycosylphosphatidylinositol (GPI)-anchored LTPg proteins. A motif analysis has placed these into four groups. With one exception, all are produced with a signal peptide and are most likely attached to the cell membrane via the GPI anchor. Several of the LTPg genes across the four groups are downregulated in syncytia induced by the beet cyst nematode Heterodera schachtii. We have here studied At3g22600 encoding LTPg5, which is the most strongly downregulated LTPg gene. It is mainly expressed in roots, and a promoter::GUS line was used to confirm the downregulation in syncytia and also showed downregulation in galls of the root knot nematode Meloidogyne incognita. In contrast, infection with bacteria (Pseudomonas syringae) and fungi (Botrytis cinerea) led to the induction of the gene in leaves. This diverse regulation of LTPg5 indicated a role in resistance, which we confirmed with overexpression lines and a T-DNA mutant. The overexpression lines were more resistant to both nematode species and to P. syringae and B. cinerea, while a knock-out mutant was more susceptible to H. schachtii and P. syringae. Thus, LTPg5 encoded by At3g22600 is part of the Arabidopsis resistance mechanism against pathogens. LTPg5 has probably no direct antimicrobial activity but could perhaps act by associating with a receptor-like kinase, leading to the induction of defense genes such as PR1.

Effect of Winter Oilseed Rape Cropping on the Development of the Sugar Beet Cyst Nematode, Heterodera schachtii, and Control of Volunteer Plants as a Trap Crop Method

The integration of oilseed rape (OSR) into sugar beet rotation systems is restricted due to the very good host status of OSR for the beet cyst nematode (BCN) Heterodera schachtii. In contrast to sugar beet, the cultivation of winter OSR covers a longer period, but at a lower soil temperature regime. Thus, presumably one or two generations of BCN may develop during the cultivation of winter OSR, resulting in moderate multiplication rates of 1–2 in the present study. This multiplication rate was year-dependent, but not affected by different sowing times. For the first time, the present study identified volunteer OSR emerging in high densities post-harvest as a major risk for a high multiplication of BCN at optimum temperatures. The emergence of BCN females with offspring was observed very early, resulting in a significant population increase before 350-degree days (>8 °C) in inoculation experiments and in field investigations. Conducting treatment trials with glyphosate to control volunteer OSR in micro-plots and field experiments confirmed effective suppression of BCN reproduction when growth of volunteer OSR was interrupted at 250–350-degree days. Thus, data gained from BCN reproduction studies under controlled and field conditions provided a unique basis for the development of a trap crop method. The degree day model has been successfully implemented as part of an open access management tool.