Parasitism of Hirsutella rhossiliensis on Different Nematodes and Its Endophytism Promoting Plant Growth and Resistance against Root-Knot Nematodes.

The endoparasitic fungus Hirsutella rhossiliensis is an important biocontrol agent of cyst nematodes in nature. To determine the potential parasitism of the fungus on a non-natural host, the pinewood nematode (Bursaphelenchus xylophilus) living in pine trees and the endophytic ability of the fungus on plants, in this paper, we first constructed and utilized a green fluorescent protein (GFP)-tagged H. rhossiliensis HR02 transformant to observe the fungal infection process on B. xylophilus and its colonization on Arabidopsis roots. Then, we compared the fungal parasitism on three species of nematodes with different lifestyles, and we found that the fungal parasitism is correlated with nematode species and stages. The parasitic effect of H. rhossiliensis on adults of B. xylophilus is similar to that on second-stage juveniles (J2) of the root-knot nematode Meloidogyne incognita after 24 h of inoculation, although the virulence of the fungus to second-stage juveniles of M. incognita is stronger than that to those of B. xylophilus and Caenorhabditis elegans. Moreover, the endophytism of H. rhossiliensis was confirmed. By applying an appropriate concentration of H. rhossiliensis conidial suspension (5 × 106 spores/mL) in rhizosphere soil, it was found that the endophytic fungus can promote A. thaliana growth and reproduction, as well as improve host resistance against M. incognita. Our results provide a deeper understanding of the fungus H. rhossiliensis as a promising biocontrol agent against plant-parasitic nematodes.

In vitro evaluation of physicochemical variables on the nematophagous fungus Duddingtonia flagrans.

Duddingtonia flagrans is a biological alternative to the use of anthelmintic drugs in ruminants. This fungus must be ingested by the animal, pass through the cavities of the digestive tract and reach the feces where it develops traps that capture the nematodes. The severe conditions encountered in this process negatively affect the fungus, which is reflected in the low recovery rates compared to the amount administered. The aim of this study was to evaluate independently the in vitro effect of typical physical and chemical conditions of the gastrointestinal cavities of ruminants on the concentration, viability, and the in vitro nematode predatory ability of the chlamydospores of D. flagrans. The factors evaluated individually were pH (2, 6, and 8), temperature (28 ± 2°C and 39 ± 2°C), exposure to artificial saliva, and milling. The results showed that the concentration and viability of D. flagrans were not affected by the action of pH, temperature, milling, or exposure to artificial saliva. Regarding the in vitro nematode predatory ability, a reduction was observed after the milling process and the exposure for 24 h at different pH.

Understanding the Transcriptional Changes During Infection of Meloidogyne incognita Eggs by the Egg-Parasitic Fungus Purpureocillium lilacinum.

The egg-pathogenic fungus Purpureocillium lilacinum parasitizes on nematode eggs, and thus, it is used as a good biocontrol agent against plant root-knot nematodes. However, little is known about the transcriptional response of P. lilacinum while infecting nematode eggs. This study presents the whole transcriptome sequencing of P. lilacinum and transcriptome-wide gene expression analysis of P. lilacinum upon infecting the eggs of Meloidogyne incognita compared to non-infecting controls. A transcriptomic library of P. lilacinum was used as reference gene set and six transcriptomic libraries of the non-infecting control and P. lilacinum infecting M. incognita eggs were constructed, respectively, comprising three biological replicates of each. A total of 1,011 differently expressed genes (DEGs) were identified in the infecting samples, including 553 up-regulated and 458 down-regulated genes compared to the non-infecting control samples. Furthermore, functional enrichment analysis exhibited that these DEGs were primarily involved in oxidative phosphorylation, oxidoreductase activity, and metabolic processes. Fifteen DEGs were randomly selected to verify the RNA sequencing results through quantitative real-time polymerase chain reaction (qPCR). The study focused on P. lilacinum genes that were strongly expressed upon infecting M. incognita eggs. These DEGs were primarily involved in detoxification, parasitic behavior, and nutritional utilization. This study contributes significantly to the understanding of the molecular mechanisms underlying the parasitic action of P. lilacinum on nematode eggs and provides a valuable genetic resource for further research on parasitic behavior of P. lilacinum. Notably, this study examined the transcriptomics of P. lilacinum infecting M. incognita eggs at only one time point. Since there were fungi at different stages of the infection process at that time point, the transcriptional profiles are not precisely examining one specific stage in this process.

Characterization of the complete mitochondrial genome of the nematophagous fungus Purpureocillium lavendulum.

The complete mitochondrial genome of Purpureocillium lavendulum was characterized in this study. This mitogenome is a closed circular molecule of 23,567 bp in length with a GC content of 28.46%, including 15 protein-coding genes, 25 transfer RNA genes, 2 ribosomal RNA genes. Phylogenetic analyses based on sequences at the 14 concatenated mitochondrial protein-coding genes showed that P. lavendulum was closely related to Hirsutella minnesotensis.

Effect of silver nanoparticles (AgNP's) from Duddingtonia flagrans on cyathostomins larvae (subfamily: cyathostominae).

The in vitro effect of silver nanoparticles of the Duddingtonia flagrans filtrate enriched with chitin was evaluated on infective larvae of cyathostomins (L3). After biosynthesis, an assay was carried out with two experimental groups in microtubes, for a period of 24 h: G1 (AgNP's-D. flagrans (43.4 µg/mL) + 120 L3) and G2 (distilled water + 120 L3). At the end of this period, AgNP's-D. flagrans (G1) demonstrated an effect on L3 with a 43% reduction (p < 0.01) in relation to G2. Thus, the authors suggest new designs with AgNP's-D. flagrans for the control of cyathostomins.

Effect of Pleurotus ostreatus (Jacq) and Trichoderma harzianum (Rifai) on Meloidogyne incognita (Kofoid & White) in tomato (Solanum lycopersicum Mill)

Two isolations of fungi from a bank of microorganisms in the Biological Sciences Laboratory at Escuela Superior Politécnica de Chimborazo were tested on the galling caused by Meloidogyne incognita in tomato seedlings grown in pots with substrate infested with a suspension of nematodes, with approximately 2000 juvenile stages (J2) from root galls of plants infested with M. incognita, taken from the Nematology laboratory of the Ecuadorian Agricultural Quality Assurance Agency (AGROCALIDAD). Pleurotus ostreatus was a fungus with nematicidal characteristics through production of toxins; while Trichoderma harzianum is a widely known fungus, although it is a plant growth promoter rather than a nematicide. The two fungi were formulated in wheat straw and rabbit manure. A complete randomized design (CRD) with three replications was used, with a chemical control (Fenamiphos) and an absolute control. Five grams of each formulation was applied per plant before the transplant. The number of galls in the roots, plant height, stem diameter, number of leaves and fresh and dry weight of the aerial part and roots of 180 tomato plants grown in greenhouse were evaluated at 60 days after transplant. The results showed that the two fungi reduced the number of galls and made it possible to obtain dry weights of the aerial and radicular part very close to the chemical control (10.09 and 3.39 g) with 8.68; 8.04; 2.96 and 3.25 g respectively. Besides Trichoderma harzianum proved to be a good promoter of root growth, therefore, the use of these bioformulates is a promising measure for the control of this phytonematode

First report of the nematicidal activity of Flammulina velutipes, its spent mushroom compost and metabolites.

The aim of the present work was to evaluate the nematicidal potential of Flammulina velutipes and its spent mushroom compost. Additionally, the nematicidal activity of enzymes and metabolites was analyzed. Isolated F. velutipes and its SMC had significant nematicidal effect on Panagrellus sp. larvae. The percentages of reduction in relation to the control group were: 69, 57.5 and 70% for SMC and 56, 24.5 and 26.6% for the isolated fungus, for 24, 48 and 72 h, respectively. The active SMC crude extract showed nematicidal action with reduction percentages of 43 and 57% for 24 and 48 h of incubation, respectively. The boiled crude extract also showed nematicidal action, however, the reduction percentages were lower than those of the active extract. This demonstrated that the nematicidal action was due to enzyme activities and other metabolites. The results demonstrated that SMC, the isolated fungus, the crude extract and the boiled crude extract showed a significant percentage of reduction on Panagrellus sp. larvae. SMC evidenced a higher nematicidal activity than the isolated fungus. In addition, nematophagous activity of F. velutipes was observed for the first time.

Reduction of bovine strongilides in naturally contaminated pastures in the southeast region of Brazil.

Biological control through the use of nematophagous fungi is a sustainable alternative for combatting helminthes in domestic animals and allows a reduction in the use of anthelmintics. The objective of this research was to evaluate the efficacy of the Arthrobotrys cladodes var macroides fungus in a pelleted formulation, based on sodium alginate and administered twice a week orally, as an alternative for the biological control of nematodes in field-grown young cattle. The experiment was conducted in a farm located in the municipality of Viçosa, MG, where 12 cattle, seven to nine months old, were allocated in two groups (treated group and control group) and distributed in pickets of Brachiaria decumbens, naturally infested with nematode larvae. The animals in the treated group received 1g of sodium alginate matrix pellets for every 10 kg of animal live weight, containing the nematophagous fungus Arthrobotrys cladodes var macroides and administered twice a week in conjunction with commercial feed. In the control group, each animal received 1 g of pellets for every 10 kg of animal live weight, without fungal mycelium added to the feed. Samples of feces and pastures were collected fortnightly for 12 months. The results showed that the most prevalent nematode genera in the coprocultures were Haemonchus sp., Cooperia sp. and Oesophagostomum sp., reflecting the results found in forage. The pasture that contained the animals that received feed with the fungus presented a reduction of 59% and 52% of larvae recovered at distances of 20 cm and 40 cm from the fecal pats, respectively. The mean number of eggs per gram of feces each month and animal body weight did not differ (p > 0.05) between the treated and control groups. Stool and soil samples from both groups were colonized by A. cladodes fungus and other fungi. Administration of Arthrobotrys cladodes var macroides mycelium by means of a sodium alginate matrix twice weekly reduced larval infestation of the surrounding pasture, indicating that this fungus may be a promising biological control of infecting forms of nematodes present in the environment.

Colonization and destruction of ants of the genus Camponotus sp. (Hymenoptera: Formicidae) in vitro by the fungus Pochonia chlamydosporia in the southeast region of Brazil.

The objective of this study was to evaluate, in vitro, the colonization and destruction of ants of the genus Camponotus sp. by the ovicidal fungus Pochonia chlamydosporia (VC4 isolate), in the southeast region of Brazil. The insects used in the experiment were worker ants of the genus Camponotus sp., collected periodically in the environment and immediately transported to the laboratory in test tubes. Then, VC4 growth was promoted in 2% chitin agar medium (2% WQ) to obtain a fungal solution containing conidia and/or chlamydospores. Two experimental groups were formed. Treated group consisted of Petri dishes containing 2% agar-water culture medium (2% WA) with nine live insects and 20 µL of fungal solution at the concentration of 15,000 conidia/chlamydospores. Control group consisted of Petri dishes containing 2% WA culture medium and nine live insects. The dishes in the treated and control groups were incubated in BOD at 25 ± 1 °C and 80 ± 10% relative humidity for 4 days. After 4 days, it was observed that the VC4 had grown, colonized, and caused the destruction of the ants. The fungus P. chlamydosporia was efficient at colonizing and destroying the urban ants collected on an experimental basis. Thus, it could open up new ways to reduce the use of chemical compounds in the future, decreasing health and environmental problems.

Complete mitogenome of the biocontroller fungus Purpureocillium sp. (Ascomycota, Ophiocordycipitaceae, Hypocreales).

The strain Purpureocillium sp. UdeA0106 is an antagonist of nematodes, fungi, and garden symphylans from crops with high economic importance in Colombia (Salazar 2013; Salazar et al. 2014; Cardona et al. 2014; Gallego et al. 2014) and is being studied to be proposed as new species. It was included on the 1000 fungal genomes project to elucidate its phylogenetic relationships with other fungi. Purpureocillium's mitogenome has 23,495 bp of circular size. It contains 15 protein-coding genes without duplications (PCGs), corresponding to the 60% of its total length, 23 transfer genes (7.6% tRNA), two of them duplicated (trnR and trnM), and two ribosomal genes (17.6% rRNA) and a GC content of 28.44%. A phylogenetic tree was proposed using their 14 PCGs mitochondrial genes and was compared with other fungi of the Subphylum Pezizomycotina. Phylogenetics relationships showed UdeA0106 to be close to P. chlamydosporia and M. anisopliae forming a cluster with other fungal biocontrol agents and separated the strain of plant pathogenic fungi.

Absorption and Emission Spectroscopic Investigation of Thermal Dynamics and Photo-Dynamics of the Rhodopsin Domain of the Rhodopsin-Guanylyl Cyclase from the Nematophagous Fungus Catenaria anguillulae.

The rhodopsin-guanylyl cyclase from the nematophagous fungus Catenaria anguillulae belongs to a recently discovered class of enzymerhodopsins and may find application as a tool in optogenetics. Here the rhodopsin domain CaRh of the rhodopsin-guanylyl cyclase from Catenaria anguillulae was studied by absorption and emission spectroscopic methods. The absorption cross-section spectrum and excitation wavelength dependent fluorescence quantum distributions of CaRh samples were determined (first absorption band in the green spectral region). The thermal stability of CaRh was studied by long-time attenuation measurements at room temperature (20.5 °C) and refrigerator temperature of 3.5 °C. The apparent melting temperature of CaRh was determined by stepwise sample heating up and cooling down (obtained apparent melting temperature: 62 ± 2 °C). The photocycle dynamics of CaRh was investigated by sample excitation to the first inhomogeneous absorption band of the CaRhda dark-adapted state around 590 nm (long-wavelength tail), 530 nm (central region) and 470 nm (short-wavelength tail) and following the absorption spectra development during exposure and after exposure (time resolution 0.0125 s). The original protonated retinal Schiff base PRSBall-trans in CaRhda photo-converted reversibly to protonated retinal Schiff base PRSBall-trans,la1 with restructured surroundings (CaRhla1 light-adapted state, slightly blue-shifted and broadened first absorption band, recovery to CaRhda with time constant of 0.8 s) and deprotonated retinal Schiff base RSB13-cis (CaRhla2 light-adapted state, first absorption band in violet to near ultraviolet spectral region, recovery to CaRhda with time constant of 0.35 s). Long-time light exposure of light-adapted CaRhla1 around 590, 530 and 470 nm caused low-efficient irreversible degradation to photoproducts CaRhprod. Schemes of the primary photocycle dynamics of CaRhda and the secondary photocycle dynamics of CaRhla1 are developed.

Toxicity and Antiviral Activity of the Extracts of Submerged Mycelium of Nematophagous Duddingtonia flagrans Fungus in Vero Cell Culture.

We studied toxicity and antiviral activity of aqueous and ethanol extracts of bioactive substances from the biomass of nematophagous fungus Duddingtonia flagrans prepared by submerged culturing of the mycelium. It is found that both extracts were characterized by low toxicity for cultured Vero cells and inhibited reproduction of DNA-viruses in this cell line. Ethanol extract of the fungus exhibited higher in vitro antiviral activity against Herpes simplex virus type 2, ectromelia virus, and vaccinia virus than water extract, which can be due to higher content of proteins, polysaccharides, flavonols, catechins, or carotenes or more effective their combination. The extracts of cultured mycelium of Duddingtonia flagrans fungus containing a complex of bioactive substances can be used for creation of broad-spectrum antiviral drugs against DNA-viruses.

Isolation, identification, and characterization of the nematophagous fungus Monacrosporium salinum from China.

Nematophagous fungi are considered to have the best potential as biological agents for the control of gastrointestinal nematodes in domestic animals. However, relatively few studies have been conducted with the genus Monacrosporium, especially with strains native to China. In the present study, we isolated and identified nematophagous fungi from fresh sheep feces. A pure fungal strain was molecularly characterized, and its nematophagous activity was evaluated. The morphological plasticity of the isolated strain, as well as its interaction with the nematode targets, was observed by scanning electron microscopy of the infected Trichostrongylus colubriformis L3 and the free-living nematode Caenorhabditis elegans. Three isolated fungal strains from the 30 fresh fecal samples of sheep from Inner Mongolia, China exhibited predatory activity; however, only a single strain was successfully purified (SF 0459). The SF 0459 strain was characterized by morphological analysis of its conidia and sequencing of its ITS1-5.8S rDNA-ITS2 region. This strain was identified to be Monacrosporium salinum (GenBank ID: KP036623). Nematophagous fungus helper bacteria were found at the interaction points between fungi and nematodes. The percentage of live T. colubriformis L3 was reduced by 83.79-88.69% based on the in vitro assay.

Incorporação ao solo de substrato contendo micélio e conídios de Pochonia chlamydosporia para o manejo de Meloidogyne javanica / Soil amendment with substrate containing mycelium and conidia of Pochonia chlamydosporia for the management of Meloidogyne javanica

Os clamidósporos são os principais propágulos utilizados como fonte de inóculo de Pochonia chlamydosporia em experimentos envolvendo o biocontrole do nematoide das galhas. O presente trabalho teve por objetivo avaliar o controle de Meloidogyne javanica em tomateiro por meio da aplicação ao solo de grãos de arroz colonizados pelo fungo contendo apenas micélio e conídio, sem a presença de clamidósporos. O isolado de P. chlamydosporia Pc-10 foi cultivado por 15 dias a 26°C em arroz previamente esterilizado em forno microondas. Dois experimentos foram conduzidos simultaneamente em casa de vegetação. No experimento 1, vasos de 2L de capacidade foram preenchidos com mistura solo:areia (1:1, v:v), contendo 3g kg-1 de solo de grãos de arroz colonizados pelo antagonista. No experimento 2, o fungo foi adicionado ao solo de vasos de 0,5L nas doses de 1, 5, 10, 15, 20, 25 ou 30g kg-1 de solo. Em seguida, o substrato de cada vaso foi infestado com 4.000 ovos de M. javanica e, após 15 dias, uma plântula de tomate foi transplantada. No experimento 1, a aplicação do fungo ao solo reduziu o número de galhas e de ovos do nematoide em 40% e 72,83%, respectivamente. No experimento 2, houve redução do número de ovos a partir de doses de 5g kg 1 de solo e no número de galhas, principalmente, nas doses de 25 e 30g kg-1 de solo. Conclui-se que P. chlamydosporia Pc-10 controlou M. javanica em tomateiro, mesmo quando aplicado ao solo na forma de grãos de arroz colonizados e sem a presença de clamidósporos.

Chlamydospores are the main propagules used as source of inoculum of Pochonia chlamydosporia in biocontrol experiments of root-knot nematodes. The objective of this study was to evaluate the control of Meloidogyne javanica on tomato plants by the soil application of rice grains colonized by Pochonia chlamydosporia containing just mycelium and conidia, without chlamydospores. The fungus (isolate Pc-10) was grown for 15 days at 26°C on grains of rice, previously sterilized in microwave oven. Two experiments were simultaneously carried out under greenhouse conditions. In the experiment 1, 2-L pots were filled with a soil:sand mixture (1:1, v:v) containing 3g kg-1 of soil of rice grains colonized by the antagonist. In the experiment 2, the fungus was added into the soil of 0.5L pots at the doses of 5, 10, 15, 20, 25 or 30g kg-1 of soil. The soil of each pot was infested with 4,000 eggs of M. javanica and one tomato seedling was transplanted in each pot after fifteen days. In the experiment 1, the application of the fungus into the soil reduced the number of galls and eggs of the nematode by 40% and 72.83%, respectively. In the experiment 2, it was observed the reduction of the number of eggs from the dose of 5 g kg-1 of soil and of the number of galls, particularly at the doses of 25 and 30g kg-1 of soil. As a conclusion, P. chlamydosporia controlled M. javanica on tomato plants even when applied into the soil as colonized-rice grains and without chlamydospores.

Sequencing and functional analysis of the genome of a nematode egg-parasitic fungus, Pochonia chlamydosporia.

Pochonia chlamydosporia is a worldwide-distributed soil fungus with a great capacity to infect and destroy the eggs and kill females of plant-parasitic nematodes. Additionally, it has the ability to colonize endophytically roots of economically-important crop plants, thereby promoting their growth and eliciting plant defenses. This multitrophic behavior makes P. chlamydosporia a potentially useful tool for sustainable agriculture approaches. We sequenced and assembled ∼41 Mb of P. chlamydosporia genomic DNA and predicted 12,122 gene models, of which many were homologous to genes of fungal pathogens of invertebrates and fungal plant pathogens. Predicted genes (65%) were functionally annotated according to Gene Ontology, and 16% of them found to share homology with genes in the Pathogen Host Interactions (PHI) database. The genome of this fungus is highly enriched in genes encoding hydrolytic enzymes, such as proteases, glycoside hydrolases and carbohydrate esterases. We used RNA-Seq technology in order to identify the genes expressed during endophytic behavior of P. chlamydosporia when colonizing barley roots. Functional annotation of these genes showed that hydrolytic enzymes and transporters are expressed during endophytism. This structural and functional analysis of the P. chlamydosporia genome provides a starting point for understanding the molecular mechanisms involved in the multitrophic lifestyle of this fungus. The genomic information provided here should also prove useful for enhancing the capabilities of this fungus as a biocontrol agent of plant-parasitic nematodes and as a plant growth-promoting organism.

Pochonia chlamydosporia: Advances and Challenges to Improve Its Performance as a Biological Control Agent of Sedentary Endo-parasitic Nematodes.

The nematophagous fungus Pochonia chlamydosporia var. chlamydosporia is one of the most studied biological control agents against plant (semi-) endo-parasitic nematodes of the genera Globodera, Heterodera, Meloidogyne, Nacobbus and, more recently, Rotylenchulus. In this paper we present highlights from more than three decades of worldwide research on this biological control agent. We cover different aspects and key components of the complex plant-fungus-nematode tri-trophic interaction, an interaction that needs to be addressed to ensure the efficient use of P. chlamydosporia as a biopesticide as part of an integrated pest management approach.

Spore production in Paecilomyces lilacinus (Thom. ) samson strains on agro-industrial residues / Produção de esporos em linhagens de Paecilomyces lilacinus (Thom. ) samson em resíduos agro-industriais

Paecilomyces lilacinus has potential for pests control. We aimed to analyze mycelial growth and spore production in P. lilacinus strains in several agro-industrial residues and commercial media. This study suggests alternative nutrient sources for fungi production and that the biotechnological potential of agro-industrial refuses could be employed in byproducts development.

Paecilomyces lilacinus apresenta potencial para controle de pragas. O objetivo deste trabalho foi analisar o crescimento micelial e a produção de esporos de linhagens de P. lilacinus em resíduos agro-industriais e meios comerciais. Este estudo sugere fontes alternativas para produção de fungos com potencial biotecnológico para desenvolvimento de bioprodutos.

Spore production in Paecilomyces lilacinus (Thom.) samson strains on agro-industrial residues.

Paecilomyces lilacinus has potential for pests control. We aimed to analyze mycelial growth and spore production in P. lilacinus strains in several agro-industrial residues and commercial media. This study suggests alternative nutrient sources for fungi production and that the biotechnological potential of agro-industrial refuses could be employed in byproducts development.

Decomposition of Plant Debris by the Nematophagous Fungus ARF.

In the study of the biological control of plant-parasitic nematodes, knowledge of the saprophytic ability of a nematophagous fungus is necessary to understand its establishment and survival in the soil. The objectives of this study were (i) to determine if the nematophagous fungus ARF (Arkansas Fungus) shows differential use of plant residues; and (ii) to determine if ARF still existed in the soil of a field in which ARF was found originally and in which the population level of Heterodera glycines had remained very low, despite 15 years of continuous, susceptible soybean. Laboratory studies of the decomposition of wheat straw or soybean root by ARF were conducted in two separate experiments, using a CO collection apparatus, where CO-free air was passed through sterilized cotton to remove the microorganisms in the air and then was passed over the samples, and evolved CO was trapped by KOH. Milligrams of C as CO was used to calculate the percentage decomposition of the plant debris by ARF. Data indicated ARF decomposed 11.7% of total organic carbon of the wheat straw and 20.1% of the soybean roots in 6 weeks. In the field soil study, 21 soil samples were taken randomly from the field. Only 3 months after the infestation of the soil with H. glycines, the percentage of parasitized eggs of H. glycines reached 64 +/- 19%, and ARF was isolated from most parasitized eggs of H. glycines. Research results indicated ARF could use plant residues to survive.

Parasitism of the Nematode Heterodera glycines by the Fungus Hirsutella rhossiliensis as Influenced by Crop Sequence.

The effect of crop sequence on parasitism of second-stage juveniles (J2) of Heterodera glycines by Hirsutella rhossiliensis was investigated. Data were collected from plots of a long-term crop rotation experiment established in 1982. Crop sequences included (i) continuous monoculture of corn and soybean; (ii) annual rotation of the two crops; and (iii) 1, 2, 3, 4, or 5 years of each crop following 5 years of the other crop. The nematode J2 density and percentage of J2 parasitized by the fungus were determined at planting, midseason, and end of season in 1997 and 1998. A significant effect of the crop sequence on parasitism of J2 was observed at midseason in both years and at end of season in 1998. In plots of first-year soybean following 5 years of corn, fungal parasitism increased from an undetectable level at planting to 2% and 4% of J2 parasitized by ends of season in 1997 and 1998, respectively. Fungal parasitism was similar in plots of second-through-fifth-year soybean after 5 years of corn and in plots of soybean monoculture. Parasitism of J2 in the soybean plots in annual rotation with corn increased from undetectable and 2% at planting to 6% and 23% at midseason in 1997 and 1998, respectively. The effect of crop sequence on the fungal parasitism of J2 may be attributed to a density-dependent relationship between the parasite and its host. Season also affected the fungal parasitism; percentage of J2 parasitized by the fungus was the highest at midseason and the lowest at planting.