Genotyping of single spore isolates of a Pasteuria penetrans population occurring in Florida using SNP-based markers.

AIMS: To generate single spore lines of a population of bacterial parasite of root-knot nematode (RKN), Pasteuria penetrans, isolated from Florida and examine genotypic variation and virulence characteristics exist within the population. METHODS AND RESULTS: Six single spore lines (SSP), 16SSP, 17SSP, 18SSP, 25SSP, 26SSP and 30SSP were generated. Genetic variability was evaluated by comparing single-nucleotide polymorphisms (SNPs) in six protein-coding genes and the 16S rRNA gene. An average of one SNP was observed for every 69 bp in the 16S rRNA, whereas no SNPs were observed in the protein-coding sequences. Hierarchical cluster analysis of 16S rRNA sequences placed the clones into three distinct clades. Bio-efficacy analysis revealed significant heterogeneity in the level virulence and host specificity between the individual clones. CONCLUSIONS: The SNP markers developed to the 5' hypervariable region of the 16S rRNA gene may be useful in biotype differentiation within a population of P. penetrans. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates an efficient method for generating single spore lines of P. penetrans and gives a deep insight into genetic heterogeneity and varying level of virulence exists within a population parasitizing a specific Meloidogyne sp. host. The results also suggest that the application of generalist spore lines in nematode management may achieve broad RKN control.

Effect of Simultaneous Water Deficit Stress and Meloidogyne incognita Infection on Cotton Yield and Fiber Quality.

Both water deficit stress and Meloidogyne incognita infection can reduce cotton growth and yield, and drought can affect fiber quality, but the effect of nematodes on fiber quality is not well documented. To determine whether nematode parasitism affects fiber quality and whether the combined effects of nematode and drought stress on yield and quality are additive (independent effects), synergistic, or antagonistic, we conducted a study for 7 yr in a field infested with M. incognita. A split-plot design was used with the main plot factor as one of three irrigation treatments (low [nonirrigated], moderate irrigation, and high irrigation [water-replete]) and the subplot factor as 0 or 56 l/ha 1,3-dichloropropene. We prevented water deficit stress in plots designated as water-replete by supplementing rainfall with irrigation. Plots receiving moderate irrigation received half the water applied to the water-replete treatment. The severity of root galling was greater in nonfumigated plots and in plots receiving the least irrigation, but the amount of irrigation did not influence the effect of fumigation on root galling (no irrigation × fumigation interaction). The weights of lint and seed harvested were reduced in nonfumigated plots and also decreased as the level of irrigation decreased, but fumigation did not influence the effect of irrigation. Nematodes affected fiber quality by increasing micronaire readings but typically had little or no effect on percent lint, fiber length (measured by HVI), uniformity, strength, elongation, length (based on weight or number measured by AFIS), upper quartile length, or short fiber content (based on weight or number). Micronaire also was increased by water deficit stress, but the effects from nematodes and water stress were independent. We conclude that the detrimental effects caused to cotton yield and quality by nematode parasitism and water deficit stress are independent and therefore additive.

A Technique to Study Meloidogyne arenaria Resistance in Agrobacterium rhizogenes-Transformed Peanut.

A reliable peanut root transformation system would be useful to study the functions of genes involved in root biology and disease resistance. The objective of this study was to establish an effective protocol to produce composite plants mediated by Agrobacterium rhizogenes transformation. In total, 75% of transformed peanut seedlings produced an average of 2.83 transgenic roots per plant. Peanut seed had the highest germination rate after treatment in a chlorine gas chamber for 8 h compared with 16 h in chlorine gas or Clorox and mercuric chloride immersion treatments. High transformation efficiency was achieved when the wound site for A. rhizogenes inoculation was covered with vermiculite instead of enclosing the whole plant in a high humidity chamber. On average, 2.5 galls from Meloidogyne arenaria infection were formed per transgenic root from susceptible genotype TifGP-2. These data indicate that A. rhizogenes-transformed roots can be used to phenotype the host response to nematode challenge. Transformation of RLP-2, a candidate resistance gene for M. arenaria integrated into a silencing construct, did not alter the resistance response of Tifguard, even though downregulation of endogenous RLP-2 expression was detected in transformed roots. It is likely that RLP-2 is not the gene conditioning M. arenaria resistance in peanut.

Toxicity of endophyte-infected tall fescue alkaloids and grass metabolites on Pratylenchus scribneri.

ABSTRACT Neotyphodium coenophialum, an endophytic fungus associated with tall fescue grass, enhances host fitness and imparts pest resistance. This symbiotum is implicated in the reduction of stresses, including plant-parasitic nematodes. To substantiate this implication, toxicological effects of root extracts, polyphenolic fraction, ergot, and loline alkaloids from endophyte-infected tall fescue were investigated using Pratylenchus scribneri, a nematode pest of tall fescue. In vitro bioassays and greenhouse studies were used as tests for effects of root fractions and compounds on motility and mortality of this lesion nematode. Greenhouse studies revealed that endophyte-infected tall fescue grasses are essentially nonhosts to P. scribneri, with root populations averaging 3 to 17 nematodes/pot, compared with 4,866 and 8,450 nematodes/pot for noninfected grasses. The in vitro assay indicated that root extracts from infected tall fescues were nematistatic. Polyphenols identified in extracts included chlorogenic acid, 3,5-dicaffeoylquinic acids, caffeic acid, and two unidentified compounds, but these were not correlated with endophyte status, qualitatively or quantitatively. Tests of several ergot alkaloids revealed that ergovaline and alpha-ergocryptine were nematicidal at 5 and 50 microg/ml, respectively, while ergocornine and ergonovine were nematistatic at most concentrations. Loline (N-formylloline), the pyrrolizidine alkaloid tested, was nematicidal (50 to 200 microg/ml). The ecological benefits of the metabolites tested here should assist in defining their role in deterring this nematode species while offering some probable mechanisms of action against plant-parasitic nematodes in general.

Resistance in Peanut Cultivars and Breeding Lines to Three Root-Knot Nematode Species.

Three major species of root-knot nematode infect peanut: Meloidogyne arenaria race 1, M. hapla, and M. javanica race 3. Sources of resistance to all three nematodes are needed for developing novel peanut cultivars with broad resistance to Meloidogyne spp. Cultivars and breeding lines of peanut were evaluated for resistance to M. arenaria, M. hapla, and M. javanica in the greenhouse and in the laboratory. Twenty-six genotypes with some resistance to M. arenaria, M. javanica, or M. hapla were identified from 60 accessions based on average eggs per gram of root and gall index relative to a susceptible control. Among these, 14 genotypes were moderately to highly resistant to all three species, 5 genotypes were resistant to M. arenaria and M. javanica, 2 genotypes were resistant to M. javanica and M. hapla, 1 genotype was resistant M. arenaria alone, and 4 genotypes were resistant to M. hapla alone. Reproduction of M. arenaria on lines NR 0817, C724-19-11, and D108 was highly variable, indicating that these genotypes likely were heterogeneous for resistance. COAN, NemaTAM, C724-25-8, and the M. arenaria-resistant plants of C724-19-11 contained the dominant sequence-characterized amplified region marker (197/909) for nematode resistance. Results with the molecular markers indicate that the high resistance to M. arenaria in GP-NC WS 6 may be different from the resistance in COAN, NemaTAM, and C724-25-8. Resistance to M. arenaria was correlated with resistance to M. javanica in peanut, whereas resistance to M. hapla was not correlated with the resistance to either M. arenaria or M. javanica. The resistant selections should be valuable sources for pyramiding resistance genes to develop new cultivars with broad and durable resistance to Meloidogyne spp.

Root vs pod infection by root-knot nematodes on aflatoxin contamination of peanut.

Aflatoxins are potent carcinogens produced by some Aspergillus spp. Infection of peanut (Arachis hypogaea) by root-knot nematodes (Meloidogyne arenaria) can lead to an increase in aflatoxin contamination of kernels when the plants are subjected to drought stress during pod maturation. It is not clear whether the increased aflatoxin contamination is primarily due to greater invasion of the galled pods by toxigenic Aspergillus spp. or whether root galling is also involved. Our objective was to determine the contribution of root and pod galling caused by root-knot nematodes to the increase in aflatoxin contamination in peanut. Two greenhouse experiments were conducted in which pods and roots were physically separated. Pod set was restricted to soil-filled pans (41 cm dia. x 10 cm depth), while the roots grew underneath the pan into a pot. The experiments had a factorial arrangement of treatments: pod zone with and without nematodes, and root zone with and without nematodes. In Experiment 1, 5000 eggs of M. arenaria were added to the root zone14 days after planting (DAP) and 8000 eggs were added to the pod zone 60 and 80 DAP. In Experiment 2, 3000 eggs were added to the root zone 30 DAP and 8000 eggs were added to the pod zone every week starting 60 DAP. The four treatment combinations were replicated 10 to 13 times. Conidia of Aspergillus flavus/A. parasiticus was added to the soil surface (pods zone) at mid bloom. Plants were subjected to drought stress 40 days before harvest. In Experiment 1, adding nematodes to the pod zone had no effect on aflatoxin concentrations in the peanut kernel. However, the lack of an effect may have been to due to the low occurrence of galling on the hulls. In pots where nematodes were added to the root zone, 50 to 80% of the root system was galled. Adding nematodes to the root zone increased aflatoxin concentrations in the peanut kernels from 34 ppb in the control to 71 ppb. In Experiment 2, there was heavy pod galling with galls present on 53% of the pods. Adding nematodes to the pod zone increased aflatoxin concentrations in the kernels from 19 ppb in the control to 572 ppb. Based on the results of the two experiments, it appears that infection of either the roots or pods by M. arenaria can lead to greater aflatoxin contamination of peanut kernels.

Root-Knot Nematode Resistance in Pearl Millet From West and East Africa.

Resistance to Meloidogyne incognita is important to provide stability to pearl millet production and to reduce nematode populations that can damage crops grown in rotation with pearl millet. The objectives of this study were to determine whether resistance to M. incognita exists in pearl millet from West and East Africa, and to determine if heterogeneity for resistance exists within selected cultivars. Resistance was assessed as nematode egg production per gram of root in greenhouse trials. Seventeen pearl millet cultivars of diverse origin were evaluated as bulk (S0) populations. All African cultivars expressed some level of resistance. P3Kollo was among the least resistant of the African cultivars, Zongo and Gwagwa were intermediate, and SoSat-C88 was among the most resistant. Thirty selfed (S1) progeny selections from SoSat-C88, Gwagwa, Zongo, and P3Kollo were evaluated for heterogeneity of resistance within cultivar. Reactions were verified in 13 S2 progeny of each of the four cultivars. In S1 evaluations, each of these cultivars was heterogeneous for resistance. Progeny reaction varied from highly resistant to highly susceptible. Patterns of apparent segregation of resistance varied among the four cultivars. Discreet resistant and susceptible phenotypes were identified in Zongo progeny, and it was estimated that two dominant genes for resistance segregated in this cultivar. Averaged across progenies, egg production on the four cultivars was less (P ≤ 0.001) than on the susceptible hybrid HGM-100, but was not different from resistant hybrid TifGrain 102. Reproduction of M. incognita on the S2 progeny tended to confirm the results from inoculations of S1 progeny. Heritability of nematode reproduction (standardized as the ratio of the value to HGM-100) determined by parent-offspring regression was 0.54. Realized heritability determined by divergent selection was 0.87.

Reproduction of Belonolaimus longicaudatus, Meloidogyne javanica, Paratrichodorus minor, and Pratylenchus brachyurus on Pearl Millet (Pennisetum glaucum).

Pearl millet (Pennisetum glaucum) has potential as a grain crop for dryland crop production in the southeastern United States. Whether or not pearl millet will be compatible in rotation with cotton (Gossypium hirsutum), corn (Zea mays), and peanut (Arachis hypogaea) will depend, in part, on its host status for important plant-parasitic nematodes of these crops. The pearl millet hybrid 'TifGrain 102' is resistant to both Meloidogyne incognita race 3 and M. arenaria race 1; however, its host status for other plant-parasitic nematodes was unknown. In this study, the reproduction of Belonolaimus longicaudatus, Paratrichodorus minor, Pratylenchus brachyurus, and Meloidogyne javanica race 3 on pearl millet ('HGM-100' and TifGrain 102) was compared relative to cotton, corn, and peanut. Separate greenhouse experiments were conducted for each nematode species. Reproduction of B. longicaudatus was lower on peanut and the two millet hybrids than on cotton and corn. Reproduction of P. minor was lower on peanut and TifGrain 102 than on cotton, corn, and HGM-100. Reproduction of P. brachyurus was lower on both millet hybrids than on cotton, corn, and peanut. Reproduction of M. javanica race 3 was greater on peanut than on the two millet hybrids and corn. Cotton was a nonhost. TifGrain 102 was more resistant than HGM-100 to reproduction of B. longicaudatus, P. minor, and M. javanica. Our results demonstrated that TifGrain 102 was a poor host for B. longicaudatus and P. brachyurus (Rf < 1) and, relative to other crops tested, was less likely to increase densities of P. minor and M. javanica.

Relationship between Meloidogyne arenaria and Aflatoxin Contamination in Peanut.

Damaged and developing kernels of peanut (Arachis hypogaea) are susceptible to colonization by fungi in the Aspergillus flavus group which, under certain conditions, produces aflatoxins prior to harvest. Our objective was to determine whether infection of peanut roots and pods by Meloidogyne arenaria increases aflatoxin contamination of the kernels when peanut is subjected to drought stress. The experiment was a completely randomized 2-x-2 factorial with 6 replicates/treatment. The treatment factors were nematodes (plus and minus M. arenaria) and fungus (plus and minus A. flavus inoculum). The experiment was conducted in 2001 and 2002 in microplots under an automatic rain-out shelter. In treatments where A. flavus inoculum was added, aflatoxin concentrations were high (> 1,000 ppb) and not affected by nematode infection; in treatments without added fungal inoculum, aflatoxin concentrations were greater (P

Reproduction of Meloidogyne spp. on Resistant Peanut Genotypes from Three Breeding Programs.

Three described species of root-knot nematode parasitize peanut (Arachis hypogaea): Meloidogyne arenaria race 1 (Ma), M. hapla (Mh), and M. javanica (Mj). Peanut cultivars with broad resistance to Meloidogyne spp. will be useful regardless of the species present in the field. The objective of this study was to determine whether peanut genotypes with resistance to M. arenaria originating from three different breeding programs were also resistant to M. hapla and M. javanica. The experiment used a factorial arrangement (completely randomized) with peanut genotype and nematode population as the factors. The five peanut genotypes were 'COAN' and AT 0812 (highly resistant to Ma), C209-6-13 (moderately resistant to Ma), and 'Southern Runner' and 'Georgia Green' (susceptible to Ma). The four nematode populations were two isolates of Ma (Gibbs and Gop) and one isolate each of Mh and Mj. On COAN or AT 0812, both Ma and Mj produced <10% of the eggs produced on Georgia Green. On the peanut genotype C209-6-13, Ma and Mj produced about 50% of the eggs produced on Georgia Green. None of the resistant genotypes exhibited a high level of resistance to Mh. The lack of resistance to Mh in any cultivars or advanced germplasm is a concern because the identity of a Meloidogyne sp. in a particular peanut field is generally not known. Breeding efforts should focus on moving genes for resistance to M. hapla into advanced peanut germplasm, and combining genes for resistance to the major Meloidogyne spp. in a single cultivar.

Evaluation of Pearl Millet Grain Hybrids for Resistance to Meloidogyne spp. and Leaf Blight Caused by Pyricularia grisea.

Pearl millet, Pennisetum glaucum, has potential as a grain crop in the southeastern United States. Our objectives were to (i) determine the resistance and/or tolerance of pearl millet hybrids to Meloidogyne incognita race 3 and M. arenaria race 1; (ii) compare reproduction of Meloidogyne spp. on pearl millet and corn; and (iii) determine the disease severity of leaf blight caused primarily by Pyricularia grisea. In a field naturally infested with M. incognita, experimental pearl millet hybrids with inbreds 114 and 117 as the pollinators had fewer numbers of second-stage juveniles and more severe leaf blight than did HGM-100, a nematode-susceptible hybrid; hybrids with inbred 115 as the pollinator were similar to HGM-100 in both nematode numbers and foliar disease severity. Grain yields in pearl millet were greater in plots treated with 1,3-dichloropropene than in control plots and were negatively correlated with leaf blight severity. In a greenhouse experiment, both M. incognita and M. arenaria produced fewer eggs on pearl millet hybrids with pollinators 114, 117, 101, 102, and 103 than on hybrid HGM-100. Reproduction of M. incognita was less on the resistant pearl millet hybrids than on corn. Because both M. incognita and P. grisea can reduce grain yield of pearl millet, hybrids developed for the southeastern United States should be resistant to both pathogens.

Influence of Cropping Systems on Stem Rot (Sclerotium rolfsii), Meloidogyne arenaria, and the Nematode Antagonist Pasteuria penetrans in Peanut.

The effect of crop rotation (main plots) and pesticide treatment (subplots) on stem rot (Sclerotium rolfsii), Meloidogyne arenaria, and the nematode antagonist Pasteuria penetrans was determined in a field experiment. The field site was naturally infested with all three organisms. Peanut (P) was rotated with 2 years of either cotton (Ct), corn (C), or bahiagrass (B). The pesticide treatments for the peanut crop were aldicarb (31 g a.i. per 100-m row), flutolanil (1.7 kg a.i./ha), aldicarb + flutolanil, and a control without either pesticide. Populations of M. arenaria were lower in peanut in the Ct-Ct-P than in P-P-P, C-C-P, or B-B-P plots and tended to be lower in plots treated with aldicarb. Abundance of P. penetrans endospores was highest in the P-P-P plots, intermediate in the B-B-P rotations, lowest in all other rotations, and was unaffected by aldicarb. The high endospore densities in the P-P-P plots may have contributed to the uncharacteristically low nematode populations in the monoculture. Incidence of stem rot in peanut was lowest in treatments with flutolanil, intermediate in the control, and highest in treatments with aldicarb alone. The greater canopy cover in aldicarb-treated plots may have created a conducive environment for S. rolfsii infection.

Resistance in Selected Corn Hybrids to Meloidogyne arenaria and M. incognita.

A total of 33 corn hybrids were evaluated in a series of greenhouse and field trials to determine if they differed in resistance to either Meloidogyne incognita race 3 or M. arenaria race 1. Reproduction of M. incognita race 3 and M. arenaria race 1 on the hybrids was also compared. Reproduction of M. arenaria differed among corn hybrids after 58 to 65 days in greenhouse experiments; however, reproduction was similar among hybrids in the field experiment. No hybrids were consistently resistant to M. incognita. Two isolates of M. arenaria and two of M. incognita were evaluated in the greenhouse trials, and no evidence of isolate-dependent resistance was observed. Meloidogyne incognita reproduced better than M. arenaria on the hybrids in this study. A survey of 102 corn fields from 11 counties throughout southern Georgia was conducted to determine the relative frequency of M. incognita and M. arenaria. Meloidogyne species were found in 34 of the fields surveyed, and 93.9% of these were identified as M. incognita. The frequency of occurrence of M. incognita was 99.6% if the previous crop was cotton and 84.6% if the previous crop was peanut. Pratylenchus spp. were extracted from all intact corn root systems examined.

Parasitism of Sedentary Stages of Heterodera glycines by Isolates of a Sterile Nematophagous Fungus.

ABSTRACT Isolates of a sterile fungus designated ARF (Arkansas fungus) can be separated into two groups, ARF-C and ARF-L, that differ morphologically and in their ability to suppress numbers of Heterodera glycines on soybean. Our objectives were to determine if the two ARF groups differed in their ability to parasitize juveniles, females, and eggs in the rhizo-sphere of soybean and to proliferate in soil. The experiments were conducted in a greenhouse using soil infested with homogenized ARF mycelium. The ARF-L isolates parasitized more juveniles and young females than did the ARF-C isolates. Suppression of these stages was 67% for ARF-L and 12% for ARF-C isolates 14 days after nematode inoculation. When soybean plants containing gravid females were transplanted into fungus-infested soil, ARF-L isolates parasitized 55 to 98% of nematode eggs, whereas ARF-C isolates parasitized 0 to 22%. In both heat-treated and nonheated soil, the biomass of mycelial mats, a measure of relative proliferation, tended to be greater for ARF-L than for ARF-C isolates. The ability of ARF-L isolates to parasitize a large percentage of both pre-reproductive stages and eggs of H. glycines may contribute to its effectiveness as a biological control agent.

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.

First Report of Pratylenchus neglectus in New York.

Soil samples were collected from a field in Wyoming County near Portageville, NY, on 29 October 1992 and 23 November 1993. The field was planted with winter wheat (Triticum aestivum L.) from September 1991 to August 1992, and with potato (Solanum tuberosum L.) cv. Superior from May 1993 to September 1993. Thirty-nine and 45 samples were collected along three transects in 1992 and 1993, respectively. Two species of Pratylenchus were identified, P. neglectus (Rensch) Filipjev & Sch. Stek. (identification confirmed by A. M. Golden) and P. penetrans (Cobb) Filipjev & Sch. Stek. Their combined population densities were 134 ± 18 (mean ± SE per 100 cm3 soil) in 1992 and 195 ± 12 in 1993. P. neglectus was found in all samples, whereas P. penetrans was found in 33 and 78% of the samples in 1992 and 1993, respectively. Where both species occurred together, the density of P. neglectus was 7 to 8 times that of P. penetrans. In both years, spores of a nematode-pathogenic bacterium (probably a Pasteuria sp.) were found attached to the cuticle of P. penetrans (68% with spores in 1993) but were rarely attached to P. neglectus (less than 1% with spores). Although both Pratylenchus spp. are widespread in North America, this is the first report of P. neglectus in New York. Its dominance in the field was unexpected because P. penetrans and P. crenatus Loof are typically the dominant Pratylenchus spp. in potato production regions of northeastern North America (1). The presence of the bacterium, which appeared to be host-specific for P. penetrans, may help explain the dominance of P. neglectus. Reference: (1) R. N. Huettel et al. Am. Potato J. 68:345, 1991.

Effect of Hirsutella rhossiliensis on Infection of Potato by Pratylenchus penetrans.

We evaluated the ability of the nematode-pathogenic fungus Hirsutella rhossiliensis (Deuteromycotina: Hyphomycetes) to reduce root penetration and population increase of Pratylenchus penetrans on potato. Experiments were conducted at 24 C in a growth chamber. When nematodes were placed on the soil surface 8 cm from a 14-day-old potato cutting, the fungus decreased the number entering roots by 25%. To determine the effect of the fungus on population increase after the nematodes entered roots, we transplanted potato cuttings infected with P. penetrans into Hirsutella-infested and uninfested soil. After 60 days, the total number of nematodes (roots and soil) was 20 +/- 4% lower in Hirsutella-infested than in uninfested soil.

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-cm(3) 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%.

Impact of a Nematode-parasitic Fungus on the Effectiveness of Entomopathogenic Nematodes.

The impact of the nematode-parasitic fungus Hirsutella rhossiliensis on the effectiveness of Steinernema carpocapsae, S. glaseri, and Heterorhabditis bacteriophora against Galleria mellonella larvae was assessed in the laboratory. The presence of Hirsutella conidia on the third-stage (J3) cuticle of S. carpocapsae and H. bacteriophora interfered with infection of insect larvae. Conidia on the J3 cuticle of S. glaseri and on the ensheathing second-stage cuticle of H. bacteriophora did not reduce the nematodes' ability to infect larvae. The LD values for S. carpocapsae, S. glaseri, and H. bacteriophora in sand containing H. rhossiliensis were not different from those in sterilized sand when Galleria larvae were added at the same time as the nematodes. However, when Galleria larvae were added 3 days after the nematodes, the LD of S. glaseri was higher in Hirsutella-infested sand than in sterilized sand, whereas the LD of H. bacteriophora was the same in infested and sterilized sand. Although the LD of S. carpocapsae was much higher in Hirsutella-infested sand than in sterilized sand, the data were too variable to detect a significant difference. These data suggest that H. bacteriophora may be more effective than Steinernema species at reducing insect pests in habitats with abundant nematode-parasitic fungi.