Arthrobotrys Dactyloides Research Articles

Efficacy of nematophagous fungi (Arthrobotrys dactyloides and A. oligospora) as biocontrol agents against root-knot nematode (Meloidogyne javanica) in sweetpotato

Efficacy of nematophagous fungi (Arthrobotrys dactyloides and A. oligospora) as biocontrol agents against root-knot nematode (Meloidogyne javanica) in sweetpotato

Genomic and Transcriptomic Analyses Revealed DdSTE2 Play a Role in Constricting Ring Formation in the Nematode-Trapping Fungi Drechslerella dactyloides.

The carnivorous fungus Drechslerella dactyloides can form constricting rings through hyphal specialization to capture nematodes. The formation of constricting rings is a prerequisite for capturing nematodes and a characteristic of entering the carnivorous stage. Currently, there is limited research on the molecular mechanism of constricting ring formation. In this study, two D. dactyloides mutants unable to form constricting rings were obtained through UV irradiation mutagenesis, and their growth and development phenotypes were compared with the wild-type strain. Transcriptome comparisons revealed differences between the mutants and the wild-type strain in metabolic pathways related to cell wall structure, peroxisomes, lipid metabolism, and MAPK signal transduction, which we validated through qPCR. We further deleted one differentially expressed gene, DdSTE2, of the MAPK pathway and confirmed its role in conidiogenesis and trap formation in D. dactyloides. Together, our results indicate that the remodeling of cell wall structure, peroxisomes, lipid metabolism, and MAPK signal transduction pathways are involved in the formation and maturation of D. dactyloides constricting rings. We discuss the implications of these results for utilizing these fungi to control animal and plant parasitic nematodes.

A palisade-shaped membrane reservoir is required for rapid ring cell inflation in Drechslerella dactyloides

Fusion of individual vesicles carrying membrane-building materials with the plasma membrane (PM) enables gradual cell expansion and shape change. Constricting ring (CR) cells of carnivorous fungi triple in size within 0.1-1 s to capture passing nematodes. Here, we investigated how a carnivorous fungus, Drechslerella dactyloides, executes rapid and irreversible PM expansion during CR inflation. During CR maturation, vesicles carrying membrane-building materials accumulate and fuse, forming a structure named the Palisade-shaped Membrane-building Structure (PMS) around the rumen side of ring cells. After CR inflation, the PMS disappears, with partially inflated cells displaying wavy PM and fully inflated cells exhibiting smooth PM, suggesting that the PMS serves as the reservoir for membrane-building materials to enable rapid and extensive PM expansion. The DdSnc1, a v-SNARE protein, accumulates at the inner side of ring cells and is necessary for PMS formation and CR inflation. This study elucidates the unique cellular mechanisms underpinning rapid CR inflation.

Multiple Roles of the Low-Affinity Calcium Uptake System in Drechslerella dactyloides, a Nematode-Trapping Fungus That Forms Constricting Rings.

(1) Background: the low-affinity calcium uptake system (LACS) has been shown to play a crucial role in the conidiation and formation of adhesive nets and knobs by nematode-trapping fungi (NTF), but its involvement in the formation of constricting rings (CRs), mechanical traps to capture free-living nematodes, remains unexplored. (2) Methods: we investigated the function of two LACS genes (DdaFIG_1 and DdaFIG_2) in Drechslerella dactyloides, an NTF that forms CRs. We generated single (DdaFIG_1Ri and DdaFIG_2Ri) and double (DdaFIG_1,2Ri) knockdown mutants via the use of RNA interference (RNAi). (3) Results: suppression of these genes significantly affected conidiation, trap formation, vegetative growth, and response to diverse abiotic stresses. The number of CRs formed by DdaFIG_1Ri, DdaFIG_2Ri, and DdaFIG_1,2Ri decreased to 58.5%, 59.1%, and 38.9% of the wild-type (WT) level, respectively. The ring cell inflation rate also decreased to 73.6%, 60.6%, and 48.8% of the WT level, respectively. (4) Conclusions: the LACS plays multiple critical roles in diverse NTF.

Characterization of the complete mitochondrial genome of the nematode-trapping fungus Drechslerella dactyloides

The complete mitochondrial genome of Drechslerella dactyloides was characterized in this study. This mitogenome is a closed circular molecule of 246860 bp in length with a GC content of 26.16%, including 87 predicted protein-coding genes, 29 transfer RNA genes, and two rRNA gens. Phylogenetic analyses based on concatenated amino acid sequences at 14 conserved mitochondrial protein-coding genes showed that D. dactyloides was closely related to Dactylellina haptotyla.

SNARE Protein DdVam7 of the Nematode-Trapping Fungus Drechslerella dactyloides Regulates Vegetative Growth, Conidiation, and the Predatory Process via Vacuole Assembly.

Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins play conserved roles in membrane fusion events in eukaryotes and have been documented to be involved in fungal growth and pathogenesis. However, little is known about the roles of SNAREs in trap morphogenesis in nematode-trapping fungi (NTF). Drechslerella dactyloides, one of the constricting ring-forming NTF, captures free-living nematodes via rapid ring cell inflation. Here, we characterized DdVam7 of D. dactyloides, a homolog of the yeast SNARE protein Vam7p. Deletion of DdVam7 significantly suppressed vegetative growth and conidiation. The mutation significantly impaired trap formation and ring cell inflation, resulting in a markedly decreased nematode-trapping ability. A large vacuole could develop in ring cells within ~2.5 s after instant inflation in D. dactyloides. In the ΔDdVam7 mutant, the vacuoles were small and fragmented in hyphae and uninflated ring cells, and the large vacuole failed to form in inflated ring cells. The localization of DdVam7 in vacuoles suggests its involvement in vacuole fusion. In summary, our results suggest that DdVam7 regulates vegetative growth, conidiation, and the predatory process by mediating vacuole assembly in D. dactyloides, and this provides a basis for studying mechanisms of SNAREs in NTF and ring cell rapid inflation. IMPORTANCE D. dactyloides is a nematode-trapping fungus that can capture nematodes through a constricting ring, the most sophisticated trapping device. It is amazing that constricting ring cells can inflate to triple their size within seconds to capture a nematode. A large centrally located vacuole is a unique signature associated with inflated ring cells. However, the mechanism underpinning trap morphogenesis, especially vacuole dynamics during ring cell inflation, remains unclear. Here, we documented the dynamics of vacuole assembly during ring cell inflation via time-lapse imaging for the first time. We characterized a SNARE protein in D. dactyloides (DdVam7) that was involved in vacuole assembly in hyphae and ring cells and played important roles in vegetative growth, conidiation, trap morphogenesis, and ring cell inflation. Overall, this study expands our understanding of biological functions of the SNARE proteins and vacuole assembly in NTF trap morphogenesis and provides a foundation for further study of ring cell rapid inflation mechanisms.

DdaCrz1, a C2H2-Type Transcription Factor, Regulates Growth, Conidiation, and Stress Resistance in the Nematode-Trapping Fungus Drechslerella dactyloides.

The Ca2+/calmodulin-dependent signaling pathway regulates diverse cellular processes. Calcineurin is a calcium-dependent phosphatase acting in fungi mainly through Crz1, a zinc finger transcription factor. Although the likely involvement of Ca2+ in fungal carnivorism has been documented, how Crz1 functions in nematode-trapping fungi remains unknown. Here, we identified the Crz1 gene (named as DdaCrz1) in Drechslerella dactyloides, a species that forms constricting rings to trap nematodes. The deletion of DdaCrz1 significantly reduced hyphal growth and conidiation, trap formation, and ring cell inflation. Moreover, the mutation increased sensitivity to Mn2+ but decreased sensitivity to Ca2+, Mg2+, Zn2+, and Li+. Similarly, the mutant showed increased tolerance to osmotic stress but was more sensitive to Congo red, a cell wall-damaging agent. Our results confirmed the critical roles of the Ca2+/calmodulin-dependent signaling pathway in regulating growth, conidiation, and the stress response, and suggested its involvement in trapping nematodes.

In vitro screening of new strains of predacious nematophagous fungi for biocontrol suitability when produced in liquid culture

Aim. To isolate, identify, and evaluate in vitro the predacious ability of nematophagous fungi strains, to determine their eligibility for mass production under submerged cultivation; to select the most efficient isolates of predacious nematopha- gous fungi as promising producers of the biopreparation to control plant-parasitic nematodes. Methods. Microbiological, microscopical, cultural-morphological, statistical. Results. The screening to determine the presence of predacious nema- tophagous fungi in different soils from different regions has been conducted for the first time in Ukraine. Out of 75 soil samples, isolated in Kyiv, Chernihiv, Dnipropetrovsk, Volyn and Odesa regions, 88 isolates of predacious nematophagous fungi were obtained which belong to 11 genera by their cultural-morphological characteristics: Arthrobotrys oligospo- ra – 39 isolates, A. musiformis – 25, A. conoides – 11, Drechslerella dactyloides – 3, A. artrobotryoides –2, A. superba – 2, A. megalospora – 2, A. sphaeroides –1, A. flagrans – 1, A. amerospora – 1, A. thaumasia – 1. High nematophagous activity in vitro (90–100 % trapping) regarding free-living nematodes (Rhabditis spp). was demonstrated by 4 isolates of A. oligospora, 18 isolates of A. musiformis, 5 isolates of A. conoides, 3 isolates of D. dactyloides, and one isolate of A. megalospora. Among the 47 most active isolates, 4 isolates of predacious fungi formed chlamydospores under submerged cultivation on two types of liquid media – wort medium and corn-molasses medium: A. musiformis-711, A. musiformis-911, A. conoides-90, D. dactyloides-19. It was found that isolate A. musiformis-911 and A. conoides-90 could form conidia in the submerged culture. Further experiments in determining the character of development for two latter isolates in different types of media under submerged cultivation established that the largest number of chlamydo- spores and conidia were formed by the isolates of A. conoides 90 and A. musiformis 911 on potato dextrose medium, 7.6·105 and 6.5·105 spores/ml respectively. In the wort medium, the productivity of spore formation for the isolate of A. conoides 90 was 35 times lower, amounting to 2.2·104 spores/ml, and in peptone-glucose medium – 90 times lower (8.5·103 spores/ml). The isolate of A. musiformis 911 in the wort medium produced 325 times fewer spores (2.0× ×103 spores/ml) than in potato-dextrose medium, while no chlamydospores and conidia were formed in the peptone- glucose medium. More detailed study of the ratio between isolates-producers and different sources of nutrition as the basis for the optimization of liquid media is required. Conclusions. According to the results of determining nematoph- agous activity regarding free-living nematodes, isolated from different soils in Ukraine and evaluating the character of development under submerged cultivation, two isolates of predacious fungi were selected – Arthrobotrys conoides-90 and A. musiformis-911, which are promising producers of a biological preparation eventually to be used in the biocon- trol of plant-parasitic nematodes. Conidia formation of the two isolates in liquid culture under mass production condi- tions was observed for the first time and could also contribute to their suitability for mass production and biocontrol.

DdaSTE12 is involved in trap formation, ring inflation, conidiation, and vegetative growth in the nematode-trapping fungus Drechslerella dactyloides.

Ste12 transcription factors, downstream of mitogen-activated protein kinase (MAPK) signalling pathways, are exclusively found in the fungal kingdom and regulate fungal mating, development, and pathogenicity. The nematode-trapping fungus Drechslerella dactyloides can capture free-living nematodes using constricting rings by cell inflation within 1 s when stimulated by nematodes entering the rings. The MAPK signalling pathways are involved in the trap formation of nematode-trapping fungi, but their downstream regulation is not clearly understood. In this study, disruption of the DdaSTE12 gene in D. dactyloides disabled cell inflation of constricting rings and led to an inability to capture nematodes. The number of septa of constricting rings and the ring cell vacuoles were changed in ΔDdaSTE12. Compared with the wild type, ΔDdaSTE12 reduced trap formation, conidiation, and vegetative growth by 79.3%, 80.3%, and 21.5%, respectively. The transcriptomes of ΔDdaSTE12-3, compared with those of the wild type, indicated that the expression of genes participating in trap formation processes, including signal transduction (Gpa2 and a 7-transmembrane receptor), vesicular transport and cell fusion (MARVEL domain-containing proteins), and nematode infection (PEX11 and CFEM domain-containing proteins), is regulated by DdaSTE12. The results suggest that DdaSTE12 is involved in trap formation and ring cell inflation, as well as conidiation and vegetative growth, by regulating a wide range of downstream functions. Our findings expanded the roles of Ste12 homologous transcription factors in the development of constricting rings and provided new insights into the downstream regulation of the MAPK signalling pathway involved in nematode predation. KEY POINTS: • DdaSTE12 was the first gene disrupted in D. dactyloides. • DdaSTE12 is related to ring cell inflation, vegetative growth, and conidiation. • DdaSTE12 deletion resulted in defects in trap formation and ring development.

English

English

Classification of dendrocola nematode-trapping fungi

Pine wilt disease, caused by Bursaphelenchus xylophilus and Bursaphelenchus mucnatus, is a serious quarantined disease. Arboreal nematode-trapping fungi of Pinus spp. are effective predators on nematodes and have strong host adaptability. The development of these fungal resources may be an effective way to control pine wood nematodes. We collected 515 samples of pine wilt disease from the areas of Ninghai City (Zhejiang province), Shuangbai County (Yunnan province), and Daxing’anling (Heilongjiang province), China. Through isolation, culture and identification, 6 species of nematode-trapping fungi (Arthrobotrys cladodesr, A. oligospora, A. musiformis, A. dendroides, Dactylellina ellipsospora, Monacrosporium thaumasium) were identified for predation against B. xylophilus, and 9 species (Arthrobotrys dactyloides, A. cladodesr A. oligospora A. dendroides, Dactylellina ellipsospora, Dactylella asthenopaga, D. leptospora, Arthrobotrys superba, Monacrosporium drechseri) were identified for predation against B. mucnatus. This study provides information in the classification of arboreal predator nematodes and provides an important basis for future biological control of pine wood nematodes.

Drechslerella dactyloides and Dactylaria brochopaga mediated structural defense in tomato plants pre-challenged with Meloidogyne incognita

The present study was undertaken with the objectives to study Drechslerella dactyloides NDAd-05 and Dactylaria brochopaga NDDb-15 mediated induction of structural defense responses leading to lower disease development and promoting growth in tomato pre-challenged with Meloidogyne incognita. The potential strains D. dactyloides NDAd-05 and D. brochopaga NDDb-15 were taken from Plant-Microbe Interaction and Rhizosphere Biology Lab, ICAR-National Bureau of Agriculturally Important Microorganisms, Kushmaur, Maunath Bhanjan, India. In vitro root colonization assay was performed using D. dactyloides NDAd-05 and D. brochopaga NDDb-15 in sand:soil culture (2:1) and significant tomato root colonization by NDAd-05 and NDDb-15 was recorded. The study elucidated multifarious effects of D. dactyloides NDAd-05 and D. brochopaga NDDb-15 when inoculated either individually or in combination in tomato plants pre-challenged with M. incognita. Additionally, D. dactyloides NDAd-05 and D. brochopaga NDDb-15 increased antioxidant as well as biocontrol activities significantly in tomato against M. incognita. Microscopic visualization of H2O2 and superoxide radicals in tomato leaves further corroborated the above findings. Further, inoculation of D. dactyloides NDAd-05 and D. brochopaga NDDb-15 activated the phenylpropanoid pathway in roots leading to increase cell wall lignifications and pectin deposition in tomato roots in addition to direct trapping and parasitizing of juveniles and adults of M. incognita. From the results it can be concluded that increased cell wall lignifications and pectin deposition probably restricted the entry of nematodes and ultimately decreased the M. incognita population in tomato roots. It was also observed that plants treated with bioagents individually or in combination modulated the phenotypical alterations and assisted plant growth promotion. This might be due to the interaction-dependent modulation of physio-biochemical pathways in the tomato plants which ultimately reduced the inoculum potential and disease intensity of M. incognita.

Drechslerella dactyloides and Dactylaria brochopaga mediated induction of defense related mediator molecules in tomato plants pre-challenged with Meloidogyne incognita

The present investigation was aimed to isolate and characterize the strains of Drechslerella dactyloides and Dactylaria brochopaga from decaying root galls of tomato in order to investigate their role in reprogramming of root apoplast that enhance defence responses in tomato pre-challenged with Meloidogyne incognita. Out of 23 strains of D. brochopaga and D. dactyloides were isolated from decaying root galls of tomato, three strains of D. dactyloides and five strains of D. brochopaga were found effective and these were selected for further characterization under controlled laboratory conditions. Further, D. dactyloides NDAd-05 and D. brochopaga NDDb-15 were found most promising strains for control of M. incognita. The study elucidates multifarious effects of D. dactyloides NDAd-05 and D. brochopaga NDDb-15 inoculated either individually or in combination on tomato plants pre-challenged with M. incognita under nethouse conditions. Results of this investigation revealed that inoculation of D. dactyloides NDAd-05 and D. brochopaga NDDb-15 increased various attributes in plants to significant degree conferring defence against M. incognita. Both the strains were found to have potential to enhance site-specific accumulation and activation of defence-related mediator molecules, enzymes and thus, exhibited biocontrol potential against M. incognita. Further, application of D. dactyloides NDAd-05 and D. brochopaga NDDb-15 not only assisted in the growth promotion but also activated phenylpropanoid pathway in root apoplast in addition to direct trapping of M. incognita.

Temporal patterns of entomopathogenic nematodes in Florida citrus orchards: Evidence of natural regulation by microorganisms and nematode competitors

The abundance of three entomopathogenic nematode (EPN) species, seven species of nematophagous fungi, free living nematode competitors of EPNs and a bacterial ectoparasite of EPNs were monitored during approximately two years in four Florida citrus orchards. The objective of the surveys was to identify natural enemies that potentially regulate the temporal abundance of naturally occurring EPNs by using molecular tools. Nematodes were extracted from two soil depths at ∼ monthly intervals, DNA extracted, and target organisms were measured using qPCR. Potentially causal relationships between the temporal patterns of EPNs and their natural enemies were assessed primarily with stepwise regression of variables at various time lags. Drechslerella dactyloides was the only nematophagous fungus species exhibiting evidence of top-down regulation, being inversely related to population change of Heterorhabditis indica at two of three sites. Acrobeloides spp. (EPN competitors) were associated with reduced population growth of Steinernema diaprepesi at two sites and H. indica was associated with reduced abundance of H. zealandica and S. diaprepesi at one site each. A Paenibacillus sp. exhibited significant phase-space, predator-prey dynamics at two of three sites with abundant S. diaprepesi, a species-specific host of the bacterium. The initial abundance of both S. diaprepesi and Paenibacillus sp. explained significant variability in population changes of S. diaprepesi in a multiple regression model at a lag of three months. Controlled experiments showed that pH is directly related to adherence of the bacterial endospores to the S. diaprepesi cuticle. Soil pH in these surveys was directly related to the infestation rate (encumbrance) by Paenibacillus and inversely related to the abundance of S. diaprepesi. Vertical distribution patterns reflected potential routes for avoiding competition and predation between species. Nematode-trapping fungi tended to inhabit shallower soil horizons than did several other nematophagous fungal species and S. diaprepesi and H. indica. The nematophagous fungus Purpureocillium lilacinum was especially abundant in deeper soil horizons and in the flatwoods sites. Depth distribution among EPNs also differed significantly with H. indica > S. diaprepesi > than H. zealandica. These results support soil pH management to conserve the demonstrated services of S. diaprepesi. They also suggest a need to better understand potential non-target effects of practices favorable to nematophagous fungi and bactivorous nematode competitors of EPNs.

Screening of different sample types associated with sheep and cattle for the presence of nematophagous fungi in China.

A total of 1502 samples, including feces of sheep (793) and cattle (348), pasture soil (118), dung compost (147) and barn soil (96), were examined between October 2012 and August 2014 to discover potential strains of nematophagous fungi for the biological control of livestock-parasitic nematodes. These samples were collected from 87 sites located in 48 counties of 20 provinces (autonomous regions/municipalities) of China. Fungi were identified down to a species level. Four hundred and seventy-seven isolates, which were distributed in 8 genera and 28 taxa, were identified as nematophagous fungi. Nematode-trapping fungi included 17 species and one unidentified species of Arthrobotrys, two of Dactylella, Drechslerella dactyloides, and Duddingtonia flagrans. Five identified species and two unidentified species of endoparasitic fungi were isolated. The predominant species from all regions were Arthrobotrys oligospora, followed by Arthrobotrys musiformis, Arthrobotrys (Monacrosporium) thaumasiun, and Arthrobotrys (Monacrosporium) microscaphoides. Species with adhesive networks were the most frequently isolated. Among the endoparasitic fungi, Podocrella harposporifera (Harposporium anguillulae) was the most common species, followed by Harposporium lilliputanum and Harposporium arcuatum. Based on Shannon diversity index, the diversity levels of nematophagous fungi were relatively higher in samples associated with cattle, barn soil, and subtropical monsoon climate zone. Three species isolated from this study, namely, Duddingtonia flagrans, Arthrobotrys salina (Monacrosporium salinum), and Arthrobotrys oligospora var. sarmatica, are newly recorded in China, and 20 species (including one unidentified species) are newly recorded in sheep and cattle barn soils worldwide.

Change in Diversity and Abundance of Nematode Destroying Fungi in Land Use under Irrigation in Selected Small Scale Irrigation Schemes in Kenya

Intensity of land cultivation is usually associated with increase in crop production and loss of soil biodiversity or its function. This study was conducted to determine the effect of intensity of land use under irrigation on the occurrence, abundance and diversity of nematode destroying fungi in selected small scale irrigation systems in Kenya. The study was conducted in four spatially separated irrigation schemes namely Kabaa and Kauti in Machakos and Kathiga Gacheru and Mbogooni) in Embu. The study areas were stratified according to land use, which included the irrigated land, rain-fed cultivated land and undisturbed land under fallow. The period of cultivation also differed with the oldest cultivated irrigation system, having been opened in 1960, while the youngest having been opened in 2011.Soil samples were collected from the study site for isolation of nematode destroying fungi. The soil sprinkle and culture technique was used to isolate soil nematode destroying fungi from the soil samples. A total of 216 fungal isolates were identified as nematode destroying fungi belonging to six genera namely Acrostalagmus, Arthrobotrys, Haptoglossa, Harposporium and Monacrosporium. All the isolates were identified resultingto nine species. 49.5% of all the fungi were isolated from irrigated land while, the rain-fed and the undisturbed land uses accounted for 29.7 and 20.8% of the isolates, respectively. The oldest irrigation systems had the least diversity (0.110) of nematode destroying fungi compared to the youngest which had a diversity index of 1.311.The species Arthrobotrys oligospora was the most frequently isolated fungus followed by Monacrosporium cionapagum with occurrence frequencies of 57 and 53%, respectively. The least frequently isolated species was Nematoctonus leiospora with an occurrence frequency of 2.3%. Of the total identified species, only Nematoctonus leiosporus and Arthrobotrys dactyloides were not affected by the irrigation activities.). From the study, it is evident that land use intensity under irrigation system and the duration of cultivation impacts on occurrence and diversity of nematode destroying fungi in the soil.

Assessment of germination and carnivorous activities of a nematode-trapping fungus Arthrobotrys dactyloides in fungistatic and fungicidal soil environment

Carnivorism is the ability of nematode-trapping fungi to trap and digest the nematodes by sophisticated devices called traps. Delivery of nematode-trapping fungi in soil for bio-control of pest nematodes often fails or gives inconsistent results. Possible reasons for failure could be the effect of soil fungistasis on germination of nematode-trapping fungi in soil environment, use of avirulent species and sensitivity of these fungi to fungicidal residues in soil. Exploitation of nematode-trapping fungi for nematode control demands that it be compatible with fungicides applied in soil or crops and proliferate in soil. This investigation represents is one of the first to evaluate the effect of fungicides on the nematode-trapping fungus Arthrobotrys dactyloides. A. dactyloides showed in vitro carnivorous potential against Meloidogyne incognita, Meloidogyne javanica, Meloidogyne graminicola, Helicotylenchus dihystera and Heterodera cajani. Conidia of A. dactyloides exposed to agricultural soils showed poor germination but formed conidial traps, which captured and killed the soil nematodes. Conidial traps, which trapped the nematodes, grew well in all soils after killing and nutrient absorption from nematode body. Soil amended with 20mg aikg−1 of carbendazim and thiram, 30mg aikg−1 of mancozeb, 50mg aikg−1 of captan, and 100mg aikg−1 of carboxin completely checked the conidial trap formation and nematode capturing. 30, 50 and 100mg aikg−1 of metalaxyl adversely affected the conidial trap formation and nematode capturing in soil. Propiconazole inhibited 15.2% conidial trap formation up to 50mg aikg−1 but caused 93.3% inhibition of conidial traps formation and complete inhibition of nematode capturing at 100mg aikg−1. Sulphur, triademefon, and tricyclazole showed least toxic effect on conidial trap formation and nematode capturing activities of A. dactyloides in soil up to 100mg aikg−1.

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.

Nematophagous fungi: Catenaria anguillulae and Dactylaria brochopaga from seed galls as potential biocontrol agents of Anguina tritici and Meloidogyne graminicola in wheat (Triticum aestivum L.)

During the course of our investigation on the selective isolation and in vitro pathogenicity tests of the nematode egg parasite and endoparasitic Catenaria anguillulae and the nematode-trapping fungus Dactylaria brochopaga against Anguina tritici, and Meloidogyne graminicola, the two biocontrol agents were also examined for their capabilities to colonize wheat seed gall and also to reduce the M. graminicola, and A. tritici in wheat (Triticum aestivum L.). Using seed galls as bait was found effective for isolating the soilborne natural colonizers of seed galls of wheat caused by A. tritici. Seed galls were found severely infested with cellulose decomposers as well as nematode trapping fungi i.e., Fusarium spp., Verticillium spp., Aspergillus spp., Penicillium spp. Arthrobotrys oligospora, Arthrobotrys superba, Arthrobotrys dactyloides, Arthrobotrys musiformis, D. brochopaga, Monacrosporium eudermatum, Stylopaga hadra, Paecilomyces spp., and C. anguillulae. Co-inoculation of D. brochopaga DBS-105, and C. anguillulae CAS101 significantly reduced the root knot and seed gall in wheat and increased the plant growth parameters including length, and dry weight of root and shoot as well as yield attributing characters like spike length; number of seed per spike, test weight etc. under greenhouse conditions as compared to pathogen challenged plants without any bioagents/chemical nematicide. These bioagents have the potential to enhance production of quality seeds of wheat being free from hazardous pesticides and thus, can further be developed into marketable formulations in order to promote eco-friendly and sustainable means of crop production.

Spatial and temporal variation in fungal endophyte communities isolated from cultivated cotton (Gossypium hirsutum).

Studies of fungi in upland cotton (Gossypium hirsutum) cultivated in the United States have largely focused on monitoring and controlling plant pathogens. Given increasing interest in asymptomatic fungal endophytes as potential biological control agents, surveys are needed to better characterize their diversity, distribution patterns and possible applications in integrated pest management. We sampled multiple varieties of cotton in Texas, USA and tested for temporal and spatial variation in fungal endophyte diversity and community composition, as well as for differences associated with organic and conventional farming practices. Fungal isolates were identified by morphological and DNA identification methods. We found members of the genera Alternaria, Colletotrichum and Phomopsis, previously isolated as endophytes from other plant species. Other recovered species such as Drechslerella dactyloides (formerly Arthrobotrys dactyloides) and Exserohilum rostratum have not, to our knowledge, been previously reported as endophytes in cotton. We also isolated many latent pathogens, but some species such as Alternaria tennuissima, Epicoccum nigrum, Acremonium alternatum, Cladosporium cladosporioides, Chaetomium globosum and Paecilomyces sp., are known to be antagonists against plant pathogens, insects and nematode pests. We found no differences in endophyte species richness or diversity among different cotton varieties, but did detect differences over time and in different plant tissues. No consistent patterns of community similarity associated with variety, region, farming practice, time of the season or tissue type were observed regardless of the ecological community similarity measurements used. Results indicated that local fungal endophyte communities may be affected by both time of the year and plant tissue, but the specific community composition varies across sites. In addition to providing insights into fungal endophyte community structure, our survey provides candidates for further evaluation as potential management tools against a variety of pests and diseases when present as endophytes in cotton and other plants.