Effectiveness of Hirsutella minnesotensis and H. rhossiliensis in control of the soybean cyst nematode in four soils with various pH,texture, and organic matter

The parasitism of soybean cyst nematode, Heterodera glycines, by the fungi Hirsutella rhossiliensis and Hirsutella minnesotensis and their biocontrol effectiveness against the nematode were investigated in four soils with various pH, texture, and organic matter. Fungal parasitism was assayed in the soils in 25 mL vials. As expected, percentage of H. glycines second-stage juveniles (J2) parasitized by either fungus increased with increasing number of fungus-colonized J2 initially added into the soils. Parasitism of J2 by the fungi was negatively related with soil pH. Both positive and negative relationships with fungal parasitism were observed for soil sandiness and organic matter. In greenhouse study, both fungi at 0.2–0.8 g fresh mycelium of liquid culture per 0.3 L pot and 1% corn-grits culture effectively reduced nematode population density. The relationship between biocontrol effectiveness and the soil factors depended on fungal species and inoculation levels. In general, percentage reduction of egg population density in the soil was negatively correlated with soil pH and positively correlated with sandiness. There was no or weak correlation between egg reduction and organic matter. The percentage of J2 parasitized by the fungi 2 months after planting did not correlate with the soil factors. Plant growth was better in the two soils with intermediate pH and sand than the soil with high pH and low sand or with low pH and high sand. It appeared that soil pH and/or texture are important in influencing biocontrol effectiveness, but further studies are needed to determine the effect of individual factors because they are correlated.     

Infection of Pratylenchus penetrans by Nematode-pathogenic fungi

Eleven fungal isolates were tested in agar dishes for pathogenicity to Pratylenchus penetrans. Of the fungi that produce adhesive conidia, Hirsutella rhossiliensis was a virulent pathogen; Verticillium balanoides, Drechmeria coniospora, and Nematoctonus sp. were weak or nonpathogens. The trapping fungi, Arthrobotrys dactyloides, A. oligospora, Monacrosporium dlipsosporum, and M. cionopagum, killed most of the P. penetrans adults and juveniles added to the fungus cultures. An isolate of Nematoctonus that forms adhesive knobs trapped only a small proportion of the nematodes. In 17-cm³ vials, soil moisture influenced survival of P. penetrans in the presence of H. rhossiliensis; nematode survival decreased with diminishing soil moisture. Hirsutella rhossiliensis and M. ellipsosporum were equally effective in reducing numbers of P. penetrans by 24-25% after 4 days in sand. After 25 days in soil artificially infested with H. rhossiliensis, numbers of P. penetrans were reduced by 28-53%.     

Trophic interactions between bacterial-feeding nematodes in plant rhizospheres and the nematophagous fungus Hirsutella rhossiliensis to suppress Heterodera schachtii

Trophic exchanges in soil food webs may suppress populations of pest organisms. We hypothesize that the suppressive condition of soils might be enhanced by manipulating components of the food web. Specifically, by enhancing populations of bacterial-feeding nematodes, propagule density of the nematophagous fungus Hirsutella rhossiliensis should increase and constrain populations of Heterodera schachtii, a plant-parasitic nematode. The rhizospheres of Crotalaria juncea and Vicia villosa stimulated population growth of the bacterial-feeding nematode, Acrobeloides bodenheimeri, but not of the nematodes Caenorhabditis elegans or Rhabditis cucumeris. The rhizospheres of Tagetes patula, Eragrostis curvula, and Sesamum indicum had no effect on any of the bacterial-feeding nematodes investigated. Acrobeloides bodenheimeri was most susceptible to parasitism by the nematophagous fungus H. rhossiliensis with 35% of individuals being parasitized in a laboratory assay. In three separate trials, parasitism of H. schachtii by H. rhossiliensis was not enhanced when populations of A. bodenheimeri were amplified in a suitable rhizosphere.     

Suppression of the Root-knot Nematode Meloidogyne javanica by Alginate Pellets Containing the Nematophagous Fungi Hirsutella rhossiliensis , Monacrosporium cionopagum and M. ellipsosporum

The endoparasitic fungus Hirsutella rhossiliensis and the nematode-trapping fungi Monacrosporium cionopagum and M. ellipsosporum were formulated as hyphae in alginate pellets. In a soil microcosm experiment, dried pellets of all three fungi decreased the invasion of cabbage seedlings by the root-knot nematode Meloidogyne javanica when juvenile nematodes were placed 2 cm from roots; M. cionopagum was more effective than the other two fungi, reducing nematode invasion by 40-95% with 0.24-0.94 pellets cm - 3 of soil. In a field microplot experiment, in which neither H. rhossiliensis nor M. ellipsosporum suppressed nematodes, 0.5 pellets of M. cionopagum cm - 3 of soil suppressed M. javanica invasion of tomato seedlings by 73%. In a second microplot experiment with only M. cionopagum , again at 0.5 pellets cm - 3 of soil, the fungus suppressed the invasion of tomato seedlings whether the pellets were added 0, 5 or 14 days before planting; the population density of M. cionopagum increased to nearly 3000 propagules g - 1 of soil by day 8 and then declined to less than 300 by day 22. Enchytraeid worms were observed in and around damaged and apparently destroyed pellets in both microplot experiments. Whether enchytraeids consumed the fungi or otherwise affected biological control requires additional research.     

Pathogenicity of Fungi to Eggs of Heterodera glycines

Twenty-one isolates of 18 fungal species were tested on water agar for their pathogenicity to eggs of Heterodera glycines. An egg-parasitic index (EPI) for each of these fungi was recorded on a scale from 0 to 10, and hatch of nematode eggs was determined after exposure to the fungi on water agar for 3 weeks at 24 C. The EPI for Verticillium chlamydosporium was 7.6, and the fungus reduced hatch 74%. Pyrenochaeta terrestris and two sterile fungi also showed a high EPI and reduced hatch 42-73%. Arthrobotrys dactyloides, Fusarium oxysporum, Paecilomyces lilacinus, Stagonospora heteroderae, Neocosmospora vasinfecta, Fusarium solani, and Exophiala pisciphila were moderately pathogenic to eggs (EPI was 2.0-4.5, and hatch was reduced 21-56%). Beauveria bassiana, Hirsutella rhossiliensis, Hirsutella thompsonii, Dictyochaeta heteroderae, Dictyochaeta coffeae, Gliocladium catenulatum, and Cladosporium sp. showed little parasitism of nematode eggs but reduced hatch. A negative correlation was observed between hatch and fungal parasitism of eggs. Fusarium oxysporum, H. rhossiliensis, P. lilacinus, S. heteroderae, V. chlamydosporium, and sterile fungus 1 also were tested in soil in a greenhouse test. After 3 months, the nematode densities were lower in soil treated with H. rhossiliensis and V. chlamydosporium than in untreated soil. The nematode population densities were correlated negatively with the EPI, but not with the percentage of cysts colonized by the fungi. Plant weights and heights generally increased in the soil treated with the fungi.     

Laboratory trials to infect insects and nematodes by some acaropathogenic Hirsutella strains (Mycota: Clavicipitaceous anamorphs)

Laboratory assays have been carried out to artificially infect insect larvae of the birch bark-beetle (Scolytus ratzeburgi Jans.-Coleoptera, Scolytidae) and codling moth Cydia pomonella L. -Lepidoptera, Tortricidae) as well as the potato cyst nematode-Globodera rostochiensis Wollenweber, sugar beet nematode-Heterodera schachtii Schmidt and root-knot nematode-Meloidogyne hapla Chif (Nematoda, Heteroderidae), by the phialoconidia of some fungal species of the genus Hirsutella. From among four species tested on insects only H. nodulosa Petch infected about 20% of S. ratzeburgi larvae, whereas H. kirchneri (Rostrup) Minter, Brady et Hall, H. minnesotensis Chen, Liu et Chen, and H. rostrata Ba?azy et Wi?niewski did not affect insect larvae. Only single eggs of the root-knot nematode were infected by H. minnesotensis in the laboratory trials, whereas its larvae remained unaffected. No infection cases of the potato cyst nematode (G. rostochiensis) and sugar beet nematode eggs were obtained. Comparisons of DNA-ITS-region sequences of the investigated strains with GenBank data showed no differences between H. minnesotensis isolates from the nematodes Heterodera glycines Ichinohe and from tarsonemid mites (authors' isolate). A fragment of ITS 2 with the sequence characteristic only for H. minnesotensis was selected. Two cluster analyses indicated close similarity of this species to H. thompsonii as sister clades, but the latter appeared more heterogenous. Insect and mite pathogenic species H. nodulosa localizes close to specialized aphid pathogen H. aphidis, whereas the phytophagous mite pathogens H. kirchneri and H. gregis form a separate sister clade. Hirsutella rostrata does not show remarkable relations to the establishment of aforementioned groups. Interrelated considerations on the morphology, biology and DNA sequencing of investigated Hirsutella species state their identification more precisely and facilitate the establishment of systematic positions.     

Population biology and biological control of nematodes.

We studied the population biology of the nematophagous fungus Hirsutella rhossiliensis to understand its potential as a biological control agent. Because the fungus is an infectious and transmissible parasite, we framed our study within an epidemiological context. Field observations, theory, and experiments demonstrated that (i) parasitism of nematodes by H. rhossiliensis is dependent on nematode density, (ii) local populations of the fungus will go extinct unless supplied with some minimum number of nematodes (the host threshold density), and (iii) natural epidemics of this fungus in populations of nematodes develop slowly and only after long periods of high host density. Additional in-depth research on population biology is needed to explain other biological control systems and to guide future research. The most effective research will combine field observation, theory, and experimentation.     

Parasitism of Heterodera schachtii and Meloidogyne javanica by Hirsutella rhossiliensis in Microplots over Two Growing Seasons

Numbers of cyst and root-knot nematodes and percentage parasitism by the nematophagous fungus Hirsutella rhossiliensis were quantified in microplots over 2 years. The microplots contained either sugarbeets in loam infested with Heterodera schachtii or tomatoes in sand infested with Meloidogyne javanica. The fungus was added to half of the microplots for each crop. Although H. rhossiliensis established in both microplot soils, the percentage of nematodes parasitized did not increase with nematode density and nematode numbers were not affected by the fungus. The results indicate that long-term interactions between populations of the fungus and cyst or root-knot nematodes will not result in biological control.     

被毛孢属两个昆虫病原真菌的重新描述

【目的】调查研究被毛孢属真菌资源,丰富该属的物种多样性,完善已知种在公共数据库中的分类信息。【方法】从贵州省发现两个分别寄生于同翅目沫蝉、鳞翅目松梢螟成虫的真菌标本GZUIFR-dj14和GZUIFR-dy1,通过形态学观察和基于tef1、ITS和28S r DNA 3个基因序列的分子生物学系统发育分析对其进行鉴定。【结果】两个病原真菌被鉴定为两个已知种,分别为长白山被毛孢(Hirsutella changbeisanensis)和雷州被毛孢(Hirsutella leizhouensis)。【结论】重新描述了这两种被毛孢的标本和无性型分离菌株,对其新寄主、新栖息地进行了报道,并补充了分子序列、系统发育分析等分类信息。     

Detection of the nematophagous fungus Hirsutella rhossiliensis in soil by real-time PCR and parasitism bioassay

Hirsutella rhossiliensis, a nematophagous fungus, has shown potential in biocontrol of plant-parasitic nematodes. Monitoring the population dynamics of a biocontrol agent in soil requires comprehensive techniques and is essential to understand how it works. Bioassay based on the fungal parasitism on the juveniles of soybean cyst nematode, Heterodera glycines, can be used to evaluate the activity of the fungus but fails to quantify fungal biomass in soil. A real-time polymerase chain reaction (PCR) assay was developed to quantify the fungal population density in soil. The assay detected as little as 100 fg of fungal genomic DNA and 40 conidia g⁻¹ soil, respectively. The parasitism bioassay and the real-time PCR assay were carried out to investigate the presence, abundance and activity of H. rhossiliensis in soil after application of different inoculum levels. Both of the percentage of assay nematodes parasitized by H. rhossiliensis based on the parasitism bioassay and the DNA yield of the fungus quantified by real-time PCR increased significantly with the increase of the inoculum levels. The DNA yield of the fungus was positively correlated with the percentage of assay nematodes parasitized by H. rhossiliensis. The combination of the two is useful for monitoring fungal biomass and activity in soil.     

Hirsutella rhossiliensisand Verticillium chlamydosporium as Biocontrol Agents of the Root-knot Nematode Meloidogyne hapla on Lettuce

Hirsutella rhossiliensis and Verticillium chlamydosporium infected second-stage juveniles (J2) and eggs of Meloidogyne hapla, respectively, in petri dishes and in organic soil in pots planted to lettuce in the greenhouse. In vitro, H. rhossiliensis produced 78 to 124 spores/infected J2 of M. hapla. The number of J2 in roots of lettuce seedlings decreased exponentially with increasing numbers of vegetative colonies of H. rhossiliensis in the soil. At an infestation of 8 M. hapla eggs/cm³ soil, 1.9 colonies of H. rhossiliensis/cm³ soil were needed for a 50% decrease in J2 penetration of lettuce roots. Egg-mass colonization with V. chlamydosporium varied from 16% to 43% when soil was infested with 8 M. hapla eggs and treated with 5,000 or 10,000 chlamydospores of V. chlamydosporium/cm³ soil. This treatment resulted in fewer J2 entering roots of bioassay lettuce seedlings planted in the infested soils after harvesting the first lettuce plants 7 weeks after infestation with M. hapla. Hirsutella rhossiliensis (0 to 4.3 colonies/cm3 soil), V. chlamydosporium (500 to 10,000 chlamydospores/cm3 soil), or their combination, added to organic soils with 8 M. hapla eggs/cm³ soil, generally did not affect lettuce weight, root galling, or egg production of M. hapla. However, when lettuce was replanted in a mix of infested and uninfested soil (1:3 and 1:7, v:v), egg production was lower in soils with V. chlamydosporium than in soils without the fungus. Both fungi have potential to reduce the M. hapla population, but at densities below 8 eggs/cm³ soil.     

Nutritional Requirements of the Nematophagous Fungus Hirsutella rhossiliensis

Six natural media were examined for growth and sporulation of six isolates of the nematophagous fungus Hirsutella rhossiliensis , using solid and/or liquid culture. Twenty carbohydrates, 19 nitrogen (N) compounds, and nine vitamins were also tested for their effects on growth, sporulation, and spore germination of a further three isolates (ATCC46487, OWVT-1 and JA16-1). Variations in nutritional requirements existed among the fungal isolates. In general, V-8 juice agar (VA), cornmeal agar and potato dextrose agar were good media for growth, and malt extract agar, VA and yeast dextrose agar were good for sporulation of all six isolates. Glycogen was the best and sucrose, inulin, D- ( + ) - trehalose and soluble starch were also good carbon (C) sources for growth and spore germination of the three isolates ATCC46487, OWVT-1 and JA16-1 in both liquid and solid culture. None of the isolates utilized D- ( + )xylose as a C source. L- sorbose, D- ribose, citric acid and D- fructose were poor for growth of all isolates. The best C source for sporulation was D- ( + )-trehalose for ATCC46487, D- sorbitol for OWVT-1 and D- ( + )-cellobiose for JA16-1. Casein was the best N source for growth of ATCC46487 and OWVT-1, while peptone was best for JA16-1. L- asparagine, L- proline, and peptone were also good for growth of all three isolates. L - cystine was not utilized by H. rhossiliensis and DL- methionine inhibited growth of all isolates. Spore germination of all isolates was well supported by most N compounds examined but was inhibited by L- cystine. No significant difference in sporulation of ATCC46487 was observed among the N sources. DL- threonine was the best N source for spore production by OWVT-1 and L- phenylalanine was best for JA16-1. Vitamins generally enhanced fungal growth and sporulation, with thiamine having the greatest influence. Excluding some vitamins individually from the medium containing all other test vitamins sometimes increased growth and/or sporulation of certain isolates.     

多毛孢属一个新种——雷州多毛孢

在雷州半岛上的湛江市郊,湖光岩畔,采到一条蔗褐蠹蛾 (Phragmatoecia castaneae Hubner)的僵硬虫尸,有孢梗束丛生。对虫尸及孢梗束进行分离,获得多毛孢属的一个新种,命名为雷州多毛孢(Hirsutella leizhouensis Fang et Tan)。本文报道该菌的形态学特征及其与近似种具疣多毛孢(H. nodulosa Petch)、褐色多毛孢(H. brownorum Mintef)的区别。     

一种寄生家蚕被毛孢的鉴定及产孢条件优化

【目的】对寄生家蚕的真菌被毛孢进行鉴定和孢子培养进行研究。【方法】采用形态特征比较和内转录间隔区(ITS)序列构建系统树进行鉴定,通过单因素筛选和正交试验进行产孢条件优化。【结果】根据形态特征比较和系统发育分析,该真菌为鹿儿岛被毛孢Hirsutella satumaensis Aoki。较优产孢条件为(质量体积比):蛋白胨3%,葡萄糖1%,蚕蛹粉1.5%,维生素B1 1%,硫酸镁0.05%,磷酸二氢钾0.1%,琼脂2%,蒸馏水1 000 mL,25°C。【结论】鹿儿岛被毛孢为已知种,文中对其显微特征进行了重新描述并补充相关分子系统学资料;产孢条件的优化可为该类群真菌孢子的获得与应用提供参考。     

Efficacy of Organic Soil Amendments for Management of Heterodera glycines in Greenhouse Experiments

In a repeated greenhouse experiment, organic soil amendments were screened for effects on population density of soybean cyst nematode (SCN), Heterodera glycines, and soybean growth. Ten amendments at various rates were tested: fresh plant material of field pennycress, marigold, spring camelina, and Cuphea; condensed distiller’s solubles (CDS), ash of combusted CDS, ash of combusted turkey manure (TMA), marigold powder, canola meal, and pennycress seed powder. Soybeans were grown for 70 d in field soil with amendments and SCN eggs incorporated at planting. At 40 d after planting (DAP), many amendments reduced SCN egg population density, but some also reduced plant height. Cuphea plant at application rate of 2.9% (amendment:soil, w:w, same below), marigold plant at 2.9%, pennycress seed powder at 0.5%, canola meal at 1%, and CDS at 4.3% were effective against SCN with population reductions of 35.2%, 46.6%, 46.7%, 73.2%, and 73.3% compared with control, respectively. For Experiment 1 at 70 DAP, canola meal at 1% and pennycress seed powder at 0.5% reduced SCN population density 70% and 54%, respectively. CDS at 4.3%, ash of CDS at 0.2%, and TMA at 1% increased dry plant mass whereas CDS at 4.3% and pennycress seed powder at 0.1% reduced plant height. For Experiment 2 at 70 DAP, amendments did not affect SCN population nor plant growth. In summary, some amendments were effective for SCN management, but phytoxicity was a concern.     

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.     

Interactions of Vesicular-Arbuscular Mycorrhizal Fungi,Phosphorus, and Heterodera glycines on Soybean

Effects of vesicular-arbuscular mycorrhizal (VAM) fungi and soil phosphorus (P) fertility on parasitism of soybean cultivars Bragg and Wright by soybean cyst nematode (SCN) were investigated in field micropiot and greenhouse experiments. VAM fungi increased height of both cultivars and yield of Wright in microplot studies in 1986 and 1987. Conversely, yield of mycorrhizal and nonmycorrhizal plants of both cultivars was suppressed by SCN. Soil population densities of SCN were unaffected by VAM fungi in 1986 but were greater in microplots infested with VAM fungi than in control microplots in 1987. Growth of Wright soybean was stimulated by VAM fungi and suppressed by SCN in greenhouse experiments. The effect of VAM fungi on SCN varied with time. Numbers of SCN in roots and soil were decreased by VAM fungi by as much as 73% at the highest SCN inoculum level through 49 days after planting. Later, however, SCN numbers were usually comparable on mycorrhizal and nonmycorrhizal plants. Soil P fertility generally had no effect on SCN. Results of a split-root experiment indicated that VAM fungal suppression of SCN was not systemic.     

Failure of a Mycelial Formulation of the Nematophagous FungusHirsutella rhossiliensisto Suppress the NematodeHeterodera schachtii

Research was conducted to determine whether pelletized hyphae ofHirsutella rhossiliensissuppressed invasion of roots by the sugarbeet cyst nematodeHeterodera schachtiiin field microplots. The loamy sand in the microplots was infested withH. schachtiibut not withH. rhossiliensis.Alginate pellets, with or without hyphae ofH. rhossiliensis,were mixed into soil removed from the microplots (1 pellet/cm³of soil). The soil was placed in cylinders positioned vertically in microplots; cylinders (6/microplot) were 10.1 cm wide and 15.3 cm deep and contained 1200 cm³of soil. Pellets and soil also were placed in soil observation chambers, which were buried in the cylinders or kept at 20°C in moisture chambers in the laboratory. After 12 days, cabbage seeds were planted in each cylinder, and after 10 days of growth, the seedlings were removed from the soil andH. schachtiiin the roots were counted. The number ofH. schachtiiin roots was large and was unaffected by addition ofH. rhossiliensis.In soil observation chambers,H. rhossiliensisgrew vigorously from the pellets in heat-treated soil but not in nonheated soil, and enchytraeids and collembolans were observed near damaged pellets. We suspect that organisms, possibly including enchytraeids and collembolans, fed upon or otherwise inhibitedH. rhossil- iensis.     

Repulsion of Meloidogyne incognita by Alginate Pellets Containing Hyphae of Monacrosporium cionopagum,M. ellipsosporum,or Hirsutella rhossiliensis

The responses of second-stage juveniles (J2) of Meloidogyne incognita race 3 to calcium alginate pellets containing hyphae of the nematophagous fungi Monacrosporiura cionopagum, M. ellipsosporum, and Hirsutella rhossiliensis were examined using cylinders (38-mm-diam., 40 or 72 mm long) of sand (94% <250-μm particle size). Sand was wetted with a synthetic soil solution (10% moisture, 0.06 bar water potential). A layer of 10 or 20 pellets was placed 4 or 20 mm from one end of the cylinder. After 3, 5, or 13 days, J2 were put on both ends, on one end, or in the center; J2 were extracted from 8-ram-thick sections 1 or 2 days later. All three fungal pellets were repellent; pellets without fungi were not. Aqueous extracts of all pellets and of sand in which fungal pellets had been incubated were repellent, but acetone extracts redissolved in water were not. Injection of CO₂ (20 μl/minute) into the pellet layer attracted J2 and increased fungal-induced mortality. In vials containing four randomly positioned pellets and 17 cm³ of sand or loamy sand, the three fungi suppressed the invasion of cabbage roots by M. javanica J2. Counts of healthy and parasitized nematodes observed in roots or extracted from soil indicated that, in the vial assay, the failure of J2 to penetrate roots resulted primarily from parasitism rather than repulsion. Data were similar whether fungal inoculum consisted of pelletized hyphae or fungal-colonized Steinernema glaseri. Thus, the results indicate that nematode attractants and repellents can have major or negligible effects on the biological control efficacy of pelletized nematophagous fungi. Factors that might influence the importance of substances released by the pellets include the strength, geometry, and duration of gradients; pellet degradation by soil microflora; the nematode species involved; and attractants released by roots.     

Variation in Efficacy of Isolates of the Fungus ARF Against the Soybean Cyst Nematode Heterodera glycines

An unnamed fungus, designated ARF, that parasitizes eggs and sedentary stages of cyst nematodes is a potential biological control agent of Heterodera glycines. The objectives of this study were to determine whether ARF isolates differ in their ability to suppress nematode numbers in soil and to compare the efficacy of ARF in heat-treated and native soil. The effectiveness of 11 ARF isolates was compared by introducing homogenized mycelium into heat-treated soil. Soybean seedlings were transplanted into pots containing fungus-infested soil and inoculated with H. glycines. After 30 or 60 days, the number of nematodes and the percentage of parasitized eggs were determined. Three isolates (907, 908, and TN14), which were previously reported to be weak egg parasites in vitro, consistently suppressed nematode numbers by 50% to 100%. Of the isolates previously reported to be aggressive egg parasites, four (903, BG2, MS3, and TN12) reduced nematode numbers by 56% to 69% in at least one experimental trial, but the other four had no effect on nematode numbers. When the efficacy of isolate TN14 was tested in heat-treated and native soil, nematode suppression was greater in the heat-treated soil in only one of two trials. In both soil treatments, nematode numbers were reduced by more than 60%. We conclude that virulence toward nematode eggs in vitro is a poor indicator of effectiveness of an ARF isolate in soil, and that the presence of soil microbes may reduce, but does not completely inhibit, activity of isolate TN14.