Effect of low-temperature stress on the survival of Meloidogyne incognita and its application in greenhouse of northern China.

We examined the effects of low temperature on egg hatching and killing rate of the 2nd instars of Meloi-dogyne incognita (J2) in the laboratory. We further evaluated the effects of two soil treatment methods on the survival rate of M. incognita in northern China in a field experiment. The results of laboratory experiment showed that survival rate of J2 was 0 after being subjected to -7 ℃ for 24 hours, and that egg hatching was completely inhibited 24 hours after being subjected to -9 ℃. The survival rate of J2 was 0 after being subjected to -1, -2, -3, and -4 ℃ for 8, 5, 3, and 1.5 d, respectively. Egg hatching was completely inhibited after being subjected to -2, -3, -4, and -5 ℃ for 9, 6, 4, and 1 d, respectively. Results of the fitting analysis showed that both the relationships between the temperature and the lethal time of J2 as well as the temperature and the non-hatching time of the eggs followed exponential functions. The results of field test showed that death rate of M. incognita in 0-50 cm soil layer after ridging treatment and 0-30 cm soil layer after leveling treatment could reach 100%, while the disease index of the former in 30-40 cm and 40-50 cm was 84.9% and 75.8%, respectively, which was lower than that in the greenhouse. Our results suggest that preventing and controlling M. incognita in greenhouses through low-tempe-rature in winter could achieve a better control effect in Yulin City and the northward region. The proposed technique is convenient and has high potential for popularization.

Meloidogyne graminicola Population Structure in China Suggests a South-to-North Expansion.

The distribution range of root-knot nematode Meloidogyne graminicola is rapidly expanding, posing a severe threat to rice production. In this study, the sequences of cytochrome oxidase subunit I (COI) genes of rice M. graminicola populations from all reported provinces in China were amplified and sequenced by PCR. The distribution pattern and phylogenetic tree showed that all 54 M. graminicola populations in China have distinct geographical distribution characteristics; specifically, cluster 1 (southern China), cluster 2 (central south and southwest China), and cluster 3 (central and eastern China). The high haplotype diversity (Hd = 0.646) and low nucleotide diversity (π = 0.00682), combined with the negative value of Tajima's D (-1.252) and Fu's Fs (-3.06764), suggested that all nematode populations were expanding. The existence of high genetic differentiation (Fst = 0.5933) and low gene flow (Nm = 0.3333) indicated that there was a block of gene exchange between most populations. Mutation accumulation with population expansion might be directly responsible for the high genetic differentiation; therefore, the tested nematode population showed high within-group genetic variation (96.30%). The haplotype Hap8 was located at the bottom of the network topology, with the widest distribution and the highest frequency (59.26%), indicating that it was the ancestral haplotype. The populations in cluster 3 were newly invasive according to the lowest frequency of occurrence of Hap8, the highest number of endemic haplotypes, and the highest total haplotype frequency (60%). In contrast, cluster 1 having the highest genetic diversity (Hd = 0.772, π = 0.01127) indicated that it was the most primitive. Interestingly, the highest gene flow (Nm > 1), lowest genetic differentiation (Fst ≤ 0.33), and closest genetic distance (0.000) only occurred between the Guangdong/Hainan population and others, which suggested that there might be channels for gene exchange between them and that long-distance dispersal occurred. This suggestion is further confirmed by the weak correlation between genetic distance and geographical distance. Based on these data, a hypothesis can be drawn that M. graminicola populations in China were spreading from south to north, specifically from Guangdong and Hainan Provinces to other regions. Natural selection (including anthropogenic) and genetic drift were the main drivers of their evolution. Coincidentally, this hypothesis was consistent with the gradual warming trend and the chronological order of reporting these populations. The main factors influencing current M. graminicola population expansion and distribution patterns might be geography, climate, long-distance seedling transport, interregional operations of agricultural machinery, and rotation mode. It reminds human beings of the necessity to be vigilant about preventing nematode disease according to local conditions all year round.

Plasmodesmata play pivotal role in sucrose supply to Meloidogyne graminicola-caused giant cells in rice.

On infection, plant-parasitic nematodes establish feeding sites in roots from which they take up carbohydrates among other nutrients. Knowledge on how carbohydrates are supplied to the nematodes' feeding sites is limited. Here, gene expression analyses showed that RNA levels of OsSWEET11 to OsSWEET15 were extremely low in both Meloidogyne graminicola (Mg)-caused galls and noninoculated roots. All the rice sucrose transporter genes, OsSUT1 to OsSUT5, were either down-regulated in Mg-caused galls compared with noninoculated rice roots or had very low transcript abundance. OsSUT1 was the only gene up-regulated in galls, at 14 days postinoculation (dpi), after being highly down-regulated at 3 and 7 dpi. OsSUT4 was down-regulated at 3 dpi. No noticeable OsSUTs promoter activities were detected in Mg-caused galls of pOsSUT1 to -5::GUS rice lines. Loading experiments with carboxyfluorescein diacetate (CFDA) demonstrated that symplastic connections exist between phloem and Mg-caused giant cells (GCs). According to data from OsGNS5- and OsGSL2-overexpressing rice plants that had decreased and increased callose deposition, respectively, callose negatively affected Mg parasitism and sucrose supply to Mg-caused GCs. Our results suggest that plasmodesmata-mediated sucrose transport plays a pivotal role in sucrose supply from rice root phloem to Mg-caused GCs, and OsSWEET11 to -15 and OsSUTs are not major players in it, although further functional analysis is needed for OsSUT1 and OsSUT4.

αß-Dehydrocurvularin isolated from the fungus Aspergillus welwitschiae effectively inhibited the behaviour and development of the root-knot nematode Meloidogyne graminicola in rice roots.

BACKGROUND: The root-knot nematode Meloidogyne graminicola has become a serious threat to rice production as a result of the cultivation changes from transplanting to direct seeding. The nematicidal activity of Aspergillus welwitschiae have been investigated in vitro, and the disease control efficacy of the active compound has been evaluated under greenhouse and field conditions. RESULTS: The active compound αß-dehydrocurvularin (αß-DC), isolated by nematicidal assay-directed fractionation, showed significant nematicidal activity against M. graminicola, with a median lethal concentration (LC50) value of 122.2 µg mL- 1. αß-DC effectively decreased the attraction of rice roots to nematodes and the infection of nematodes and also suppressed the development of nematodes under greenhouse conditions. Moreover, αß-DC efficiently reduced the root gall index under field conditions. CONCLUSIONS: To our knowledge, this is the first report to describe the nematicidal activity of αß-DC against M. graminicola. The results obtained under greenhouse and field conditions provide a basis for developing commercial formulations from αß-DC to control M. graminicola in the future.

Transcriptional profiling of wheat (Triticum aestivum L.) during a compatible interaction with the cereal cyst nematode Heterodera avenae.

Cereal cyst nematode (CCN, Heterodera avenae) presents severe challenges to wheat (Triticum aestivum L.) production worldwide. An investigation of the interaction between wheat and CCN can greatly improve our understanding of how nematodes alter wheat root metabolic pathways for their development and could contribute to new control strategies against CCN. In this study, we conducted transcriptome analyses of wheat cv. Wen 19 (Wen19) by using RNA-Seq during the compatible interaction with CCN at 1, 3 and 8 days past inoculation (dpi). In total, 71,569 transcripts were identified, and 10,929 of them were examined as differentially expressed genes (DEGs) in response to CCN infection. Based on the functional annotation and orthologous findings, the protein phosphorylation, oxidation-reduction process, regulation of transcription, metabolic process, transport, and response process as well as many other pathways previously reported were enriched at the transcriptional level. Plant cell wall hydrolysis and modifying proteins, auxin biosynthesis, signalling and transporter genes were up-regulated by CCN infection to facilitate penetration, migration and syncytium establishment. Genes responding to wounding and jasmonic acid stimuli were enriched at 1 dpi. We found 16 NBS-LRR genes, 12 of which were down-regulated, indicating the repression of resistance. The expression of genes encoding antioxidant enzymes, glutathione S-transferases and UDP-glucosyltransferase was significantly up-regulated during CCN infection, indicating that they may play key roles in the compatible interaction of wheat with CCN. Taken together, the results obtained from the transcriptome analyses indicate that the genes involved in oxidation-reduction processes, induction and suppression of resistance, metabolism, transport and syncytium establishment may be involved in the compatible interaction of Wen 19 with CCN. This study provides new insights into the responses of wheat to CCN infection. These insights could facilitate the elucidation of the potential mechanisms of wheat responses to CCN.

Isolation and characterization of Aspergillus niger NBC001 underlying suppression against Heterodera glycines.

Heterodera glycines is the most pervasive soybean pests worldwide. Biocontrol provides a strategy to sustainably control nematodes. In this study, 22 fungal isolates were obtained and identified from cysts of Heterodera spp. Among them, Aspergillus niger NBC001 showed high nematicidal activity against H. glycines. The 2-fold dilution of NBC001 culture filtrate caused 89% mortality of second-stage juveniles and inhibited more than 98% of egg hatching in vitro. In both pot and field experiments, the numbers of H. glycines cysts in soybean seedlings dressed with the the 5-fold concentrated culture filtrate of NBC001 were significantly reduced by 43% and 28%, respectively. In addition, application of NBC001 remarkably reduced the penetration of nematodes into the roots. Histochemical and fluorometric staining analyses indicate that application of NBC001 stimulated hydrogen peroxide activity in the roots and triggered callose deposition in the leaves and roots. Transcription of the PR1a and EREBP genes in the salicylic acid and ethylene signaling pathways was upregulated in soybean plants treated with NBC001. However, the application of concentrated culture filtrate of NBC001 had no significant impacts on the soil microbial community based on next generation DNA sequencing technology. In summary, NBC001 may be a good biocontrol agent against H. glycines via stimulation of the immunity/defense of the plant host.

Priming effect of root-applied silicon on the enhancement of induced resistance to the root-knot nematode Meloidogyne graminicola in rice.

BACKGROUND: Silicon (Si) can confer plant resistance to both abiotic and biotic stress. In the present study, the priming effect of Si on rice (Oryza sativa cv Nipponbare) against the root-knot nematode Meloidogyne graminicola and its histochemical and molecular impact on plant defense mechanisms were evaluated. RESULTS: Si amendment significantly reduced nematodes in rice roots and delayed their development, while no obvious negative effect on giant cells was observed. Increased resistance in rice was correlated with higher transcript levels of defense-related genes (OsERF1, OsEIN2 and OsACS1) in the ethylene (ET) pathway. Si amendment significantly reduced nematode numbers in rice plants with enhanced ET signaling but had no effect in plants deficient in ET signaling, indicating that the priming effects of Si were dependent on the ET pathway. A higher deposition of callose and accumulation of phenolic compounds were observed in rice roots after nematode attack in Si-amended plants than in the controls. CONCLUSION: These findings indicate that the priming effect may partially depend on the production of phenolic compounds and hydrogen peroxide. Further research is required to model the ethylene signal transduction pathway that occurs in the Si-plant-nematode interaction system and gain a better understanding of Si-induced defense in rice.

Effects of a NTG-based chemical mutagenesis on the propamocarb-tolerance of the nematophagous fungus Lecanicillium attenuatum.

Lecanicillium attenuatum is an important nematophagous fungus with potential as a biopesticide for control of plant-pathogenic nematodes. However, relatively low fungicide-tolerance limits its application in the field. To improve the propamocarb-tolerance of L. attenuatum, a NTG-based mutagenesis system was established. Among different combinations of NTG concentration and treatment time in the first-round NTG treatment, the treatment of 1.0mg/ml NTG for 60min gave a proper conidial lethality rate of 84.6% and the highest positive mutation rate of 7.7%, and then produced the highest propamocarb-tolerant mutant LA-C-R1-T4-M whose EC50 value reached to 1050.0µg/ml. The positive mutation range was 105.1% in the first-round NTG treatment. Multiple-round NTG treatment was further employed to enhance the propamocarb tolerance of L. attenuatum. The positive mutation range was significantly accumulated to 179.3% on the third-round NTG treatment, and then appeared to level-off and remained constant. These results indicated that multiple-round NTG treatment had a significant accumulative effect on fungal tolerance to propamocarb. Among all chemical-mutants, the LA-C-R3-M was the highest tolerant to propamocarb, whose EC50 value was increased 2.79-fold compared to the wild-type strain, and it was mitotic stable after 20 passages on PDA medium. Colony growth, conidia yield and conidial germination on plates, and parasitism of nematode eggs of M. incognita and H. glycines were not significantly changed by the NTG-based mutagenesis compared to the wild-type strain in either single- or multiple-round NTG treatment. In conclusion, we succeeded in improving the propamocarb tolerance of L. attenuatum via the optimized NTG-based mutagenesis system. The improved strain LA-C-R3-M could be potentially applied with propamocarb in the field.

Efficacy Evaluation of Seed-Coating Compounds Against Cereal Cyst Nematodes and Root Lesion Nematodes on Wheat.

Cereal cyst nematodes (Heterodera avenae and H. filipjevi) and root lesion nematodes (Pratylenchus spp.) have been found to infect cereals in 16 provinces of China. To develop a nematicide that effectively controls nematodes, two novel chemical products, methylene bis thiocyanate (MBT) and MBT + thiamethoxam (MTT); four common pesticides, fipronil + chlorpyrifos (FIC), emamectin benzoate, imidacloprid, and Bacillus thuringiensis; and one fungicide, iprodione, were tested as seed coatings for the control of cereal cysts and root lesion nematodes from 2013 to 2015. Wheat seeds were treated with these seven seed coatings before sowing, and changes in the numbers of Heterodera spp. and Pratylenchus spp. were recorded during three different growth stages. Wheat yields were also compared after harvest. All treatments reduced the numbers of Pratylenchus in wheat and of cysts and eggs of Heterodera in the soil compared with the untreated control. Among the treatments, application of MTT or FIC was more effective than that of the other treatments for nematode control, and the other treatments had similar effects. The results of this study have demonstrated that MTT and FIC applied as seed treatments effectively reduce the number of cysts, inhibit the reproduction of Heterodera and Pratylenchus, and enhance wheat yields. MTT and FIC are thus suitable for controlling nematodes on wheat under natural field conditions.

Mutations in Acetylcholinesterase2 (ace2) increase the insensitivity of acetylcholinesterase to fosthiazate in the root-knot nematode Meloidogyne incognita.

The root-knot nematode Meloidogyne incognita causes severe damage to continuously cropping vegetables. The control of this nematode relies heavily on organophosphate nematicides in China. Here, we described resistance to the organophosphate nematicide fosthiazate in a greenhouse-collected resistant population (RP) and a laboratory susceptible population (SP) of M. incognita. Fosthiazate was 2.74-fold less toxic to nematodes from RP than that from SP. Quantitative real-time PCR revealed that the acetylcholinesterase2 (ace2) transcription level in the RP was significantly higher than that in the SP. Eighteen nonsynonymous amino acid differences in ace2 were observed between the cDNA fragments of the RP and SP. The acetylcholinesterase (AChE) protein activity in the RP was significantly reduced compared with that in the SP. After knocking down the ace2 gene, the ace2 transcription level was significantly decreased, but no negative impact on the infection of juveniles was observed. The 50% lethal concentration of the RNAi RP population decreased 40%, but the inhibition rate of fosthiazate against AChE activity was significantly increased in RP population. Thus, the increased fosthiazate insensitivity in the M. incognita resistant population was strongly associated with mutations in ace2. These results provide valuable insights into the resistance mechanism of root-knot nematode to organophosphate nematicides.

Genetic improvement of the nematicidal fungus Lecanicillium attenuatum against Heterodera glycines by expression of the Beauveria bassiana Cdep1 protease gene.

Lecanicillium attenuatum is an important nematophagous fungus with potential as a biopesticide against plant-parasitic nematodes. The Pr1A-like cuticle-degrading protease (Cdep1) gene originating from the entomopathogenic fungus Beauveria bassiana was transformed into the nematophagous fungus L. attenuatum using a polyethylene-glycol mediated protoplast-based transformation system. Protease activity was increased 0.64- to 1.63-fold 2-10d after growth in the transformed L. attenuatum. Inhibition of egg-hatching and J2 motility of soybean cyst nematodes (Heterodera glycines) by cell-free fungal culture filtrates were enhanced by 17-76% 2-14d and 43-152% 1-13d after incubation, respectively.

Establishment of polyethylene-glycol-mediated protoplast transformation for Lecanicillium lecanii and development of virulence-enhanced strains against Aphis gossypii.

BACKGROUND: Lecanicillium lecanii has been developed as a biopesticide and used in biological control of several agricultural insects. To improve fungal virulence, an optimised polyethylene glycol (PEG)-mediated protoplast transformation system was established for L. lecanii. Pr1A-like cuticle-degrading protease gene (Cdep1) from Beauveria bassiana was transferred into L. lecanii, and its resulting activity against Aphis gossypii was assessed. RESULTS: The optimised protoplast generation yielded 2.5 × 10(8) protoplasts g(-1) wet mycelium of fungi, and gave nearly 98% viability and 80% regeneration on plates. Protease activities were increased about fivefold in transformants expressing CDEP1. The median lethal concentration (LC50 ) for transformants expressing CDEP1 was twofold lower than that for the wild type (WT). The median survival time (LT50 ) for transformants expressing CDEP1 was also 14.2% shorter than that for WT, though no significant difference. There were no significant differences in conidial germination as colony growth and conidial yield on plates between transformants expressing CDEP1 and WT. The transformants expressing CDEP1 grew significantly quicker than WT in insects. The transformants expressing CDEP1 were lower in conidial yields on insect cadavers, but insignificantly different from WT. CONCLUSION: The PEG-mediated protoplast transformation system was effective for L. lecanii, and the expression of CDEP1 significantly enhanced fungal virulence against cotton aphids. © 2016 Society of Chemical Industry.

Large-scale identification of wheat genes resistant to cereal cyst nematode Heterodera avenae using comparative transcriptomic analysis.

BACKGROUND: Cereal cyst nematode Heterodera avenae, an important soil-borne pathogen in wheat, causes numerous annual yield losses worldwide, and use of resistant cultivars is the best strategy for control. However, target genes are not readily available for breeding resistant cultivars. Therefore, comparative transcriptomic analyses were performed to identify more applicable resistance genes for cultivar breeding. METHODS: The developing nematodes within roots were stained with acid fuchsin solution. Transcriptome assemblies and redundancy filteration were obtained by Trinity, TGI Clustering Tool and BLASTN, respectively. Gene Ontology annotation was yielded by Blast2GO program, and metabolic pathways of transcripts were analyzed by Path_finder. The ROS levels were determined by luminol-chemiluminescence assay. The transcriptional gene expression profiles were obtained by quantitative RT-PCR. RESULTS: The RNA-sequencing was performed using an incompatible wheat cultivar VP1620 and a compatible control cultivar WEN19 infected with H. avenae at 24 h, 3 d and 8 d. Infection assays showed that VP1620 failed to block penetration of H. avenae but disturbed the transition of developmental stages, leading to a significant reduction in cyst formation. Two types of expression profiles were established to predict candidate resistance genes after developing a novel strategy to generate clean RNA-seq data by removing the transcripts of H. avenae within the raw data before assembly. Using the uncoordinated expression profiles with transcript abundance as a standard, 424 candidate resistance genes were identified, including 302 overlapping genes and 122 VP1620-specific genes. Genes with similar expression patterns were further classified according to the scales of changed transcript abundances, and 182 genes were rescued as supplementary candidate resistance genes. Functional characterizations revealed that diverse defense-related pathways were responsible for wheat resistance against H. avenae. Moreover, phospholipase was involved in many defense-related pathways and localized in the connection position. Furthermore, strong bursts of reactive oxygen species (ROS) within VP1620 roots infected with H. avenae were induced at 24 h and 3 d, and eight ROS-producing genes were significantly upregulated, including three class III peroxidase and five lipoxygenase genes. CONCLUSIONS: Large-scale identification of wheat resistance genes were processed by comparative transcriptomic analysis. Functional characterization showed that phospholipases associated with ROS production played vital roles in early defense responses to H. avenae via involvement in diverse defense-related pathways as a hub switch. This study is the first to investigate the early defense responses of wheat against H. avenae, not only provides applicable candidate resistance genes for breeding novel wheat cultivars, but also enables a better understanding of the defense mechanisms of wheat against H. avenae.

Persistence and Viability of Lecanicillium lecanii in Chinese Agricultural Soil.

The entomopathogenic fungus L. lecanii has been developed as biopesticides and used widely for biological control of several insects in agricultural practice. Due to the lack of isolation/count methods for L. lecanii in soil, the persistence of this fungus in soil appears to have attracted no attention. A selective medium and count method for L. lecanii in soil based on cetyl trimethyl ammonium bromide (CTAB) was developed, and then the persistence and viability of this fungus in soil were investigated under field conditions between 2012 and 2014. The results showed that the rate of recovery for L. lecanii in soil on the selective CTAB medium was satisfactory. The minimum CFUs for L. lecanii on the selective medium (0.5 g/L CTAB) was about 102 conidia/g soil. The L. lecanii density in soil declined quickly in the first month after inoculation with fungal conidia, kept stable for 6 to 10 months, and then decreased gradually until undetectable. L. lecanii could persist for at least 14 months in the agricultural soil of northern China. The colony growth, conidia yield and germination rate on plates, as well as the median lethal concentration or times (LC50 or LT50) to aphids, mycelium growth in aphids and sporulation on aphids of L. lecanii did not change significantly during the persistence in soil. In general, the count method developed here was a very useful tool for monitoring the dynamics of natural or introduced L. lecanii populations in soil, and the data on the persistence of L. lecanii in soil reported here were helpful for biological control and environmental risk assessment.

Agrobacterium tumefaciens-mediated transformation in the entomopathogenic fungus Lecanicillium lecanii and development of benzimidazole fungicide resistant strains.

Lecanicillium lecanii has been used in the biological control of several insects in agricultural practice. Since the gene manipulation tools for this entomopathogenic fungus have not been sufficiently developed, Agrobacterium tumefaciens-mediated transformation (ATMT) in L. lecanii was investigated in this study, using the wild-type isolate FZ9906 as a progenitor strain and the hygromycin B resistance (hph) gene as a selection marker. Furthermore, a field carbendazim-resistant (mrt) gene from Botrytis cinerea was expressed in L. lecanii FZ9906 via the ATMT system. The results revealed that the frequency of transformation surpassed 25transformants/10(6) conidia, most of the putative transformants contained a single copy of T-DNA, and the T-DNA inserts were stably inherited after five generations. All putative transformants had indistinguishable biological characteristics relative to the wild-type strain, excepting two transformants with altered growth habits or virulence. Moreover, the resistance of the putative transformants to carbendazim (MBC) was improved, and the highest one was 380-fold higher than the wild-type strain. In conclusion, ATMT is an effective and suitable system for L. lecanii transformation, and will be a useful tool for the basic and application research of gene functions and gene modifications of this strain.

Global dissection of alternative splicing in paleopolyploid soybean.

Alternative splicing (AS) is common in higher eukaryotes and plays an important role in gene posttranscriptional regulation. It has been suggested that AS varies dramatically among species, tissues, and duplicated gene families of different sizes. However, the genomic forces that govern AS variation remain poorly understood. Here, through genome-wide identification of AS events in the soybean (Glycine max) genome using high-throughput RNA sequencing of 28 samples from different developmental stages, we found that more than 63% of multiexonic genes underwent AS. More AS events occurred in the younger developmental stages than in the older developmental stages for the same type of tissue, and the four main AS types, exon skipping, intron retention, alternative donor sites, and alternative acceptor sites, exhibited different characteristics. Global computational analysis demonstrated that the variations of AS frequency and AS types were significantly correlated with the changes of gene features and gene transcriptional level. Further investigation suggested that the decrease of AS within the genome-wide duplicated genes were due to the diminution of intron length, exon number, and transcriptional level. Altogether, our study revealed that a large number of genes were alternatively spliced in the soybean genome and that variations in gene structure and transcriptional level may play important roles in regulating AS.

Efficacy evaluation of fungus Syncephalastrum racemosum and nematicide avermectin against the root-knot nematode Meloidogyne incognita on cucumber.

The root-knot nematode (RKN) is one of the most damaging agricultural pests.Effective biological control is need for controlling this destructive pathogen in organic farming system. During October 2010 to 2011, the nematicidal effects of the Syncephalastrum racemosum fungus and the nematicide, avermectin, alone or combined were tested against the RKN (Meloidogyne incognita) on cucumber under pot and field condition in China. Under pot conditions, the application of S. racemosum alone or combined with avermectin significantly increased the plant vigor index by 31.4% and 10.9%, respectively compared to the M. incognita-inoculated control. However, treatment with avermectin alone did not significantly affect the plant vigor index. All treatments reduced the number of root galls and juvenile nematodes compared to the untreated control. Under greenhouse conditions, all treatments reduced the disease severity and enhanced fruit yield compared to the untreated control. Fewer nematodes infecting plant roots were observed after treatment with avermectin alone, S. racemosum alone or their combination compared to the M. incognita-inoculated control. Among all the treatments, application of avermectin or S. racemosum combined with avermectin was more effective than the S. racemosum treatment. Our results showed that application of S. racemosum combined with avermectin not only reduced the nematode number and plant disease severity but also enhanced plant vigor and yield. The results indicated that the combination of S. racemosum with avermectin could be an effective biological component in integrated management of RKN on cucumber.

Occurrence and Development of the Cereal Cyst Nematode (Heterodera avenae) in Shandong, China.

The cereal cyst nematode (CCN), Heterodera aveane, has been found in 16 provinces of China, including the Shandong winter-wheat-growing region. This study investigated the population dynamics of H. avenae in the winter wheat 'Jimai 22' and 'Tainong 18' for two consecutive years in the field. Soil and root samples were collected during the winter-wheat-growing season and H. avenae population densities and life-stages determined. H. avenae population dynamics in roots and soil of the two winter wheat cultivars were similar over the 2-year period. Second-stage juvenile (J2) population densities in wheat roots were greatest during booting stage (April), when mean soil temperature was between 11.8 and 14.4°C. Cysts in rhizosphere soil increased significantly when new cysts were formed after Zadoks (Z) 47 (booting stage). There was a peak in J2 population densities in soil during Z23 and Z30 (tillering and stem elongation, respectively) whereas J2 population densities were the lowest at Z13 (seedling stage). This research provides important information indicating that J2 populations in roots and soil increased after the wheat winter dormancy period. Knowledge of when different life stages of H. avenae occur in winter wheat in Shandong will provide valuable insights to enable the development of an integrated approach to manage this plant-parasitic nematode.

Exploring the host parasitism of the migratory plant-parasitic nematode Ditylenchus destuctor by expressed sequence tags analysis.

The potato rot nematode, Ditylenchus destructor, is a very destructive nematode pest on many agriculturally important crops worldwide, but the molecular characterization of its parasitism of plant has been limited. The effectors involved in nematode parasitism of plant for several sedentary endo-parasitic nematodes such as Heterodera glycines, Globodera rostochiensis and Meloidogyne incognita have been identified and extensively studied over the past two decades. Ditylenchus destructor, as a migratory plant parasitic nematode, has different feeding behavior, life cycle and host response. Comparing the transcriptome and parasitome among different types of plant-parasitic nematodes is the way to understand more fully the parasitic mechanism of plant nematodes. We undertook the approach of sequencing expressed sequence tags (ESTs) derived from a mixed stage cDNA library of D. destructor. This is the first study of D. destructor ESTs. A total of 9800 ESTs were grouped into 5008 clusters including 3606 singletons and 1402 multi-member contigs, representing a catalog of D. destructor genes. Implementing a bioinformatics' workflow, we found 1391 clusters have no match in the available gene database; 31 clusters only have similarities to genes identified from D. africanus, the most closely related species to D. destructor; 1991 clusters were annotated using Gene Ontology (GO); 1550 clusters were assigned enzyme commission (EC) numbers; and 1211 clusters were mapped to 181 KEGG biochemical pathways. 22 ESTs had similarities to reported nematode effectors. Interestedly, most of the effectors identified in this study are involved in host cell wall degradation or modification, such as 1,4-beta-glucanse, 1,3-beta-glucanse, pectate lyase, chitinases and expansin, or host defense suppression such as calreticulin, annexin and venom allergen-like protein. This result implies that the migratory plant-parasitic nematode D. destructor secrets similar effectors to those of sedentary plant nematodes. Finally we further characterized the two D. destructor expansin proteins.

[Effects of transgenic crops on soil microorganisms: a review].

The worldwide cultivation of transgenic crops not only provides tremendous economic benefits, but also induces the concern about the potential risks of transgenic crops on soil ecosystem in which microorganisms are involved. The potential effects of transgenic crops on soil microorganisms include the direct effects of the transgenic proteins on non-target soil microorganisms, and the indirect effects of the unintentional changes in the chemical compositions of root exudates induced by the introduction of the exogenous transgenic proteins. Most of the studies on transgenic crops suggested that transgenic crops could affect the quantity and structure of soil microbial populations. However, the perceivable effects on the soil microorganisms are inconsistent, with some in significant and others in non-significant, or some with persistent and others with non-persistent. This paper summarized the effects of different transgenic crops on soil microorganisms, and discussed the factors affecting the assessment reliability, including the species of transgenic crops and the experimental technologies and principles. Some issues needed to be paid special attention to in the future studies were put forward.