Selective control of parasitic nematodes using bioactivated nematicides.

Parasitic nematodes are a major threat to global food security, particularly as the world amasses 10 billion people amid limited arable land1-4. Most traditional nematicides have been banned owing to poor nematode selectivity, leaving farmers with inadequate means of pest control4-12. Here we use the model nematode Caenorhabditis elegans to identify a family of selective imidazothiazole nematicides, called selectivins, that undergo cytochrome-p450-mediated bioactivation in nematodes. At low parts-per-million concentrations, selectivins perform comparably well with commercial nematicides to control root infection by Meloidogyne incognita, a highly destructive plant-parasitic nematode. Tests against numerous phylogenetically diverse non-target systems demonstrate that selectivins are more nematode-selective than most marketed nematicides. Selectivins are first-in-class bioactivated nematode controls that provide efficacy and nematode selectivity.

Chia: Host Status for Meloidogyne incognita and Activity of Plant Extracts.

Chia (Salvia hispanica L.) seeds are used for food, drinks, oil, and animal feed, and all plant parts are employed in traditional medicine. The growing demand for the seed has created a need for improved disease management. Plant-parasitic nematodes have been found on other Salvia spp., but none have been reported from S. hispanica. Chia has also not been tested for production of compounds active against these nematodes. Therefore, aqueous extracts from shoots and roots of six chia lines, Brad's Organic, Cono, E2, G3, G5, and W13.1, were tested in laboratory assays. Some concentrations of all extracts were nematotoxic, killing about one-third of Meloidogyne incognita (Kofoid & White) Chitwood second-stage juveniles (J2s) in shoot extracts and up to nearly half of J2s in root extracts. Hatch was generally not affected by the extracts. In greenhouse trials, all six chia lines were hosts of M. incognita. Chia line G3 had approximately two times or more eggs per gram of root than Brad's Organic or Cono. When cucumber seedlings were transplanted into soil amended with chopped chia shoots (2.3 or 2.5% weight of fresh shoots/weight of dry soil), galling and egg production on cucumber roots were not suppressed. To our knowledge, this is the first report that chia is a host to M. incognita (or any phytoparasitic nematode) and that chia shoots and roots produce compounds active against a nematode.

Festulolium and fungal endophyte associations: host status for Meloidogyne incognita and nematotoxic plant extracts.

Festulolium hybrids are forage grasses used worldwide in temperate climates. They are associated with the fungal endophyte Epichloë uncinata, which aids in nutrient uptake, drought tolerance, and production of metabolites that protect against parasites and herbivores. Epichloë uncinata produces loline alkaloids, which can deter insect pests. Festulolium has not been widely studied for susceptibility to plant-parasitic nematodes, so Festulolium lines, with and without fungal endophytes, were tested in the greenhouse for host status to the root-knot nematode Meloidogyne incognita. All were poor hosts, regardless of line or endophyte status. Pepper seedlings planted into soil following removal of the Festulolium plants were infected by nematodes, likely because of surviving nematodes from the original inoculation combined with some reproduction on Festulolium. Lolines were found in shoots and roots of all endophyte-associated lines, and some types of lolines in roots increased after nematode infection. Methanolic extracts from roots and shoots of a tested Festulolium line did not inhibit egg hatch, but killed nearly a third of second-stage juveniles whether an endophyte was present or not. Further studies would indicate whether these Festulolium lines aid in suppressing field populations of M. incognita.Festulolium hybrids are forage grasses used worldwide in temperate climates. They are associated with the fungal endophyte Epichloë uncinata, which aids in nutrient uptake, drought tolerance, and production of metabolites that protect against parasites and herbivores. Epichloë uncinata produces loline alkaloids, which can deter insect pests. Festulolium has not been widely studied for susceptibility to plant-parasitic nematodes, so Festulolium lines, with and without fungal endophytes, were tested in the greenhouse for host status to the root-knot nematode Meloidogyne incognita. All were poor hosts, regardless of line or endophyte status. Pepper seedlings planted into soil following removal of the Festulolium plants were infected by nematodes, likely because of surviving nematodes from the original inoculation combined with some reproduction on Festulolium. Lolines were found in shoots and roots of all endophyte-associated lines, and some types of lolines in roots increased after nematode infection. Methanolic extracts from roots and shoots of a tested Festulolium line did not inhibit egg hatch, but killed nearly a third of second-stage juveniles whether an endophyte was present or not. Further studies would indicate whether these Festulolium lines aid in suppressing field populations of M. incognita.

Nematotoxicity of Paeonia spp. Extracts and Camellia oleifera Tea Seed Cake and Extracts to Heterodera glycines and Meloidogyne incognita.

Tea-oil camellia (Camellia oleifera) is grown for tea seed oil production, with tea seed cake produced as a byproduct. Rather than disposing of the cake, agricultural uses increase the value of oil production. Constituents of C. oleifera are also utilized for traditional Chinese medicine, as are compounds produced by tree peony roots. Consequently, the unused C. oleifera cake, and stems from two tree peony species, Paeonia rockii and Paeonia suffruticosa, were studied for compounds antagonistic to soybean cyst nematode (Heterodera glycines) and root-knot nematode (Meloidogyne incognita). Extracts from C. oleifera cake and P. rockii stems suppressed hatch and were nematotoxic to second-stage juveniles (J2) of both nematode species. P. rockii extracts were more effective than P. suffruticosa extracts for decreasing M. incognita hatch and J2 viability. In greenhouse trials with soybean (Glycine max 'Essex'), powdered C. oleifera cake applied as a soil amendment suppressed H. glycines cysts/g root by up to 66% compared with nonamended controls. These results indicate that the extracts and cake contain compounds active against H. glycines and M. incognita, with activity varying between the two Paeonia species. C. oleifera tea seed cake, and constituents of the cake or of P. rockii, are candidates for further studies on management of these nematodes.

Activity of Vetiver Extracts and Essential Oil against Meloidogyne incognita.

Vetiver, a nonhost grass for certain nematodes, was studied for the production of compounds active against the southern root-knot nematode, Meloidogyne incognita . In laboratory assays studying the effects on second-stage juvenile (J2) activity and viability, crude vetiver root and shoot extracts were nematotoxic, resulting in 40% to 70% J2 mortality, and were also repellent to J2. Vetiver oil did not exhibit activity against J2 in these assays. Gas chromatography-mass spectrometry analyses of three crude vetiver root ethanol extracts and a commercial vetiver oil determined that two of the major components in each sample were the sesquiterpene acid 3,3,8,8-tetramethyltricyclo[5.1.0.0(2,4)]oct-5-ene-5-propanoic acid and the sesquiterpene alcohol 6-isopropenyl-4,8a-dimethyl-1,2,3,5,6,7,8,8a-octahydronaphthalen-2-ol. The acid was present in higher amounts in the extracts than in the oil. These studies demonstrating nematotoxicity and repellency of vetiver-derived compounds to M. incognita suggest that plant chemistry plays a role in the nonhost status of vetiver to root-knot nematodes, and that the chemical constituents of vetiver may be useful for suppressing nematode populations in the soil.

New Nematotoxic Indoloditerpenoid Produced by Gymnoascus reessii za-130.

Chemical investigation of the fungal strain Gymnoascus reessii za-130, which was previously isolated from the rhizosphere of tomato plants infected by the root-knot nematode Meloidogyne incognita, led to the isolation and identification of a new indoloditerpenoid metabolite designated gymnoascole acetate. Its structure was established by spectroscopic methods including 1D- and 2D-NMR and MS analyses. Gymnoascole acetate demonstrated strong adverse effects on M. incognita second-stage juvenile (J2) viability; exposure to 36 µg/mL for 24 h induced 100% paralysis of J2 (EC50 = 47.5 µg/mL). Gymnoascole acetate suppressed M. incognita egg hatch relative to controls by >90% at 133 µg/mL after 7 days of exposure. The numbers of root galls and J2 in both soil and roots were significantly reduced (p = 0.05) by treatment with 2-200 µg/mL gymnoascole acetate/kg soil, compared to untreated control plants; nematode suppression increased with gymnoascole acetate concentration. This study demonstrated the nematotoxicity of gymnoascole acetate and indicates that it might be a potential biobased component in integrated management of M. incognita.

Synthesis and Biological Evaluation of 3,5-Dimethoxystilbene Analogs.

In our continuing effort to discover natural product-based pest management agents, derivatives of 3,5-dimethoxystilbene were synthesized yielding 27 new and six known compounds. Compounds 11 and 12 showed strong Aedes aegypti larvicidal activity (LC50 45.31 and 49.93 µm, respectively). Furthermore, 11 and 12 exhibited high effectiveness against larvae of pesticide-susceptible and pyrethroid-resistant strains of Ae. aegypti; activity against the adult mosquitoes was low. Compounds 6f, 6g, and 6i at either 83.3 or 166.7 µg/ml reduced the mobility of second-stage juveniles (J2) of the root-knot nematode (Meloidogyne incognita) that hatched from eggs immersed in the test compounds for 7 days. However, there was little or no effect on J2 placed directly into these compounds, and none of the analogs suppressed M. incognita egg hatch. The compounds were tested for inhibition of some agriculturally important fungi; 6a, 7a, and 7e demonstrated strong inhibition of Colletotrichum species. Activity of the stilbenes against some human pathogens was also explored; 11, 12, and 16 showed moderate inhibitory activity against Cryptococcus neoformans, Staphylococcus aureus, methicillin-resistant S. aureus, and Mycobacterium intracellulare. Except for 11 and 12, which were active against mosquito larvae and some human pathogens, no single analog demonstrated activity in all the tests, indicating specific activities. Synthesis of the analogs and structure-activity relationships are discussed.

Assessment of DAPG-producing Pseudomonas fluorescens for Management of Meloidogyne incognita and Fusarium oxysporum on Watermelon.

Pseudomonas fluorescens isolates Clinto 1R, Wayne 1R, and Wood 1R, which produce the antibiotic 2,4-diacetylphloroglucinol (DAPG), can suppress soilborne diseases and promote plant growth. Consequently, these beneficial bacterial isolates were tested on watermelon plants for suppression of Meloidogyne incognita (root-knot nematode: RKN) and Fusarium oxysporum f. sp. niveum (Fon). In a greenhouse trial, Wayne 1R root dip suppressed numbers of RKN eggs per gram root on 'Charleston Gray' watermelon by 28.9%. However, in studies focused on 'Sugar Baby' watermelon, which is commercially grown in Maryland, a Wayne 1R root dip did not inhibit RKN reproduction or plant death caused by Fon. When all three isolates were applied as seed coats, plant stand in the greenhouse was reduced up to 60% in treatments that included Fon ± P. fluorescens, and eggs per gram root did not differ among treatments. In a microplot trial with Clinto 1R and Wayne 1R root dips, inoculation with P. fluorescens and/or Fon resulted in shorter vine lengths than treatment with either P. fluorescens isolate plus RKN. Root weights, galling indices, eggs per gram root, and second-stage juvenile (J2) numbers in soil were similar among all RKN-inoculated treatments, and fruit production was not affected by treatment. Plant death was high in all treatments. These studies demonstrated that the tested P. fluorescens isolates resulted in some inhibition of vine growth in the field, and were not effective for enhancing plant vigor or suppressing RKN or Fon on watermelon.

Isolation and identification of nematode-antagonistic compounds from the fungus Aspergillus candidus.

Culture medium from an isolate of the fungus Aspergillus candidus was extracted, fractionated and examined to discover compounds antagonistic to plant-parasitic nematodes that are important pathogens of agricultural crops. Column, thin layer and preparative chromatographies and spectral and elemental analyses, were used to isolate and identify two major constituents of an active fraction (Fraction F) obtained from the medium. Compound 1 was identified as 2-hydroxypropane-1, 2, 3-tricarboxylic acid (citric acid). Compound 2 was identified as 3-hydroxy-5-methoxy-3-(methoxycarbonyl)-5-oxopentanoic acid, an isomer of 1, 2-dimethyl citrate. Compound 1 and a citric acid standard, each tested at 50 mg mL(-1) in water, decreased hatch from eggs of the plant-parasitic nematode Meloidogyne incognita by more than 94%, and completely immobilized second-stage juveniles after 4-6 days exposure. Fraction F and Compounds 1 and 2 decreased the mobility of adults of the plant-parasitic nematode Ditylenchus destructor in vitro. Fraction F (25 mg mL(-1)) inhibited mobility >99% at 72 hrs. Compounds 1 and 2 (50 mg mL(-1)) each inhibited mobility more than 25% at 24 hr and more than 50% at 72 hr. This is the first assignment of nematode-antagonistic properties to specifically identified A. candidus metabolites.

Nematotoxicity of drupacine and a Cephalotaxus alkaloid preparation against the plant-parasitic nematodes Meloidogyne incognita and Bursaphelenchus xylophilus.

BACKGROUND: Species of Cephalotaxus (the plum yews) produce nematotoxic compounds of unknown identity. Consequently, bioassay-guided fractionation was employed to identify the compound(s) in Cephalotaxus fortunei twigs and leaves with activity against plant-parasitic nematodes. RESULTS: A crude alkaloid extract, particularly drupacine, was responsible for much of the nematotoxicity. The ED50 of drupacine for Bursaphelenchus xylophilus was 27.1 µg mL⁻¹, and for Meloidogyne incognita it was 76.3 µg mL⁻¹. Immersion of M. incognita eggs in 1.0 mg mL⁻¹ crude alkaloid extract (the highest tested concentration) reduced hatch by 36%; immersion of second-stage juveniles (J2) resulted in 72-98% immobility. Crude alkaloid extract and drupacine suppressed protease activity in extracts of the microbivorous nematode Panagrellus redivivus by 50% and 80%, respectively. Application of 0.02-0.5 mg mL⁻¹ crude alkaloid extract to soil with M. incognita inoculum did not significantly reduce pepper plant shoot length or weight, compared with nematode-inoculated, water-treated controls, but the number of eggs and J2 per root system respectively decreased by 69% and 73% at 0.5 mg mL⁻¹. CONCLUSION: Drupacine and a crude alkaloid extract suppress nematode hatch, activity of mixed life stages, and population numbers on plant roots. This is the first demonstration of nematotoxicity of crude Cephalotaxus alkaloids and drupacine.

Sunn hemp cover cropping and organic fertilizer effects on the nematode community under temperate growing conditions.

Field experiments were conducted in Maryland to investigate the influence of sunn hemp cover cropping in conjunction with organic and synthetic fertilizers on the nematode community in a zucchini cropping system. Two field treatments, zucchini planted into a sunn hemp living and surface mulch (SH) and zucchini planted into bare-ground (BG) were established during three field seasons from 2009 to 2011. In 2009, although SH slightly increased nematode richness compared with BG by the first harvest (P < 0.10), it reduced nematode diversity and enrichment indices (P < 0.01 and P < 0.10, respectively) and increased the channel index (P < 0.01) compared to BG at the final harvest. This suggests a negative impact of SH on nematode community structure. The experiment was modified in 2010 and 2011 where the SH and BG main plots were further split into two subplots to investigate the added influence of an organic vs. synthetic fertilizer. In 2010, when used as a living and surface mulch in a no-till system, SH increased bacterivorous, fungivorous, and total nematodes (P < 0.05) by the final zucchini harvest, but fertilizer type did not influence nematode community structure. In 2011, when incorporated into the soil before zucchini planting, SH increased the abundance of bacterivorous and fungivorous nematodes early in the cropping season. SH increased species richness also at the end of the season (P < 0.05). Fertilizer application did not appear to influence nematodes early in the season. However, in late season, organic fertilizers increased enrichment and structure indices and decreased channel index by the end of the zucchini cropping cycle.

Post-transcriptional gene silencing of root-knot nematode in transformed soybean roots.

RNAi constructs targeted to four different genes were examined to determine their efficacy to reduce galls formed by Meloidogyne incognita in soybean roots. These genes have high similarity with essential soybean cyst nematode (Heterodera glycines) and Caenorhabditis elegans genes. Transformed roots were challenged with M. incognita. Two constructs, targeted to genes encoding tyrosine phosphatase (TP) and mitochondrial stress-70 protein precursor (MSP), respectively, strongly interfered with M. incognita gall formation. The number of galls formed on roots transformed with constructs targeting the M. incognita TP and MSP genes was reduced by 92% and 94.7%, respectively. The diameter of M. incognita inside these transformed roots was 5.4 and 6.5 times less than the diameter of M. incognita found inside control plants transformed with the empty vector. These results indicate that silencing the genes encoding TP and MSP can greatly decrease gall formation and shows a promising solution for broadening resistance of plants against this plant-parasitic nematode.

Mustard seed meal mixtures: management of Meloidogyne incognita on pepper and potential phytotoxicity.

Meals produced when oil is extracted from seeds in the Brassicaceae have been shown to suppress weeds and soilborne pathogens. These seed meals are commonly used individually as soil amendments; the goal of this research was to evaluate seed meal mixes of Brassica juncea (Bj) and Sinapis alba (Sa) against Meloidogyne incognita. Seed meals from Bj 'Pacific Gold' and Sa 'IdaGold' were tested alone and in combinations to determine rates and application times that would suppress M. incognita on pepper (Capsicum annuum) without phytotoxicity. Rates of soil application (% w/w) for the phytotoxicity study were: 0.5 Sa, 0.2 Bj, 0.25 Sa + 0.25 Bj, 0.375 Sa + 0.125 Bj, 0.125 Sa + 0.375 Bj, and 0, applied 0 - 5 weeks before transplant. Overall, 0.2% Bj was the least toxic meal to pepper seedlings. By comparison, 0.5% S. alba seed meal did not reduce lettuce (Lactuca sativa) seed germination at week 0, but all seed meal treatments containing B. juncea prevented or significantly reduced germination at week 0. The seed meals did not affect lettuce seed germination at weeks 1-5, but hypocotyl growth was reduced by all except 0.2% Bj at weeks 1, 4 and 5. Brassica juncea and Sa meals were tested for M. incognita suppression at 0.2, 0.15, 0.1 and 0.05%; mixtures were 0.1% Sa + 0.1% Bj, 0.15% Sa + 0.05% Bj, and 0.05% Sa + 0.15% Bj. All treatments were applied 2 weeks before transplant. The 0.2% Bj and 0.05% Sa + 0.15% Bj treatments overall had the longest shoots and highest fresh weights. Eggs per g root were lowest with 0.1 - 0.2% Bj amendments and the seed meal mixtures. The results indicate that Bj and some Bj + Sa mixtures can be applied close to transplant to suppress M. incognita populations on pepper; consequently, a seed meal mixture could be selected to provide activity against more than one pest or pathogen. For pepper, care should be taken in formulating mixtures so that Sa rates are low compared to Bj.

Impact of No-till Cover Cropping of Italian Ryegrass on Above and Below Ground Faunal Communities Inhabiting a Soybean Field with Emphasis on Soybean Cyst Nematodes.

Two field trials were conducted between 2008 and 2010 in Maryland to evaluate the ability of an Italian ryegrass (IR) (Lolium multiflorum) cover crop to reduce populations of plant-parasitic nematodes while enhancing beneficial nematodes, soil mites and arthropods in the foliage of a no-till soybean (Glycine max) planting. Preplant treatments were: 1) previous year soybean stubble (SBS); and 2) herbicide-killed IR cover crop + previous year soybean stubble (referred to as IR). Heterodera glycines population densities were very low and no significant difference in population densities of H. glycines or Pratylenchus spp. were observed between IR and SBS. Planting of IR increased abundance of bacterivorous nematodes in 2009. A reverse trend was observed in 2010 where SBS had higher abundance of bacterivorous nematodes and nematode richness at the end of the cover cropping period. Italian ryegrass also did not affect insect pests on soybean foliage. However, greater populations of spiders were found on soybean foliage in IR treatments during both field trials. Potential causes of these findings are discussed.

Selection of genetically diverse Trichoderma spp. isolates for suppression of Phytophthora capsici on bell pepper.

Environmentally compatible control measures are needed for suppression of Phytophthora capsici on pepper. Twenty-three isolates of Trichoderma were screened for suppression of a mixture of 4 genetically distinct isolates of this pathogen on bell pepper (Capsicum anuum) in greenhouse pot assays. Of these 23 isolates, GL12, GL13, and Th23 provided significant suppression of P. capsici in at least 2 assays. These isolates were then compared with Trichoderma virens isolates GL3 and GL21 for suppression of this disease in the presence and absence of the harpin-based natural product Messenger. Isolates GL3 and Th23 provided significant disease suppression (P ≤ 0.05) in 3 of 4 assays, while GL12, GL13, and GL21 provided significant suppression in 2 of 4 assays. There was no apparent benefit from the application of Messenger. Phylogenetic analysis of these 5 isolates (based on the ITS1 region of the nuclear rDNA cluster and tef1), and an additional 9 isolates that suppressed P. capsici in at least 1 assay, separated isolates into 2 clades, with 1 clade containing GL3, GL12, GL13, and GL21. There were also 2 more distantly related isolates, one of which was Th23. We report here the identification of genetically distinct Trichoderma isolates for potential use in disease management strategies employing isolate combinations directed at suppression of P. capsici on pepper.

Toxicity of 2,4-diacetylphloroglucinol (DAPG) to plant-parasitic and bacterial-feeding nematodes.

The antibiotic 2,4-diacetylphloroglucinol (DAPG) is produced by some isolates of the beneficial bacterium Pseudomonas fluorescens. DAPG is toxic to many organisms, and crop yield increases have been reported after application of DAPG-producing P. fluorescens. This study was conducted to determine whether DAPG is toxic to selected nematodes. The plant-parasitic nematodes Heterodera glycines, Meloidogyne incognita, Pratylenchus scribneri and Xiphinema americanum, and the bacterial-feeding nematodes Caenorhabditis elegans, Pristionchus pacificus, and Rhabditis rainai, were immersed in concentrations ranging from 0 to 100 µg/ml DAPG. Egg hatch and viability of juveniles and adults were determined. DAPG was toxic to X. americanum adults, with an LD50 of 8.3 µg/ml DAPG. DAPG decreased M. incognita egg hatch, but stimulated C. elegans hatch during the first hours of incubation. Viability of M. incognita J2 and of C. elegans J1 and adults was not affected. There were no observed effects on the other nematodes. The study indicated that DAPG is not toxic to all nematodes, and did not affect the tested species of beneficial bacterial-feeding nematodes. Augmentation of DAPG-producing P. fluorescens populations for nematode biocontrol could be targeted to specific nematode species known to be affected by this compound and by other antibiotics produced by the bacteria, or these bacteria could be used for other possible effects, such as induced plant resistance.

Dose-response effects of clove oil from Syzygium aromaticum on the root-knot nematode Meloidogyne incognita.

BACKGROUND: Clove oil, derived from the plant Syzygium aromaticum (L.) Merr. & Perry, is active against various organisms, and was prepared in a soy lecithin/detergent formulation to determine concentrations active against the root-knot nematode Meloidogyne incognita (Kofoid and White) Chitwood. RESULTS: In microwell assays, the mean effective clove oil concentration that reduced egg hatch by 50% (EC(50)) was 0.097% (v/v) clove oil; the EC(50) for second-stage juvenile (J2) viability was 0.145% clove oil (compared with carrier control treatments). Volatiles from 5.0% clove oil reduced nematode egg hatch in water by 30%, and decreased viability of hatched J2 by as much as 100%. Reductions were not as large with nematodes in carrier. In soil trials with J2 recovered from Baermann funnels, the EC(50) = 0.192% clove oil (compared with water controls). CONCLUSION: The results demonstrated that the tested formulation is active against M. incognita eggs and J2, that the EC(50) values for J2 in the microwell studies and the soil recovery tests were similar to each other and that direct contact with the clove oil is needed for optimal management results with this natural product.

Velvetbean (Mucuna pruriens) extracts: impact on Meloidogyne incognita survival and on Lycopersicon esculentum and Lactuca sativa germination and growth.

Velvetbean (Mucuna spp.) is a summer annual that has been used as a cover crop to reduce erosion, fix nitrogen and suppress weeds and plant-parasitic nematodes. Crude aqueous extracts (1:15 dry weight plant/volume water) were made from velvetbean plant parts, and various concentrations of the extracts were evaluated in vitro for toxicities to different stages of Meloidogyne incognita (Kofoid and White) Chitwood and for suppression of hypocotyl and root growth and inhibition of germination of tomato (Lycopersicon esculentum L.) and lettuce (Lactuca sativa L.). Germination was only affected by the full-strength extract from leaf blades. Lettuce root growth was the most sensitive indicator of allelopathic activity of the plant part extracts. Lettuce and tomato root growth was more sensitive to the extract from main roots than to extracts of other plant parts, with lethal concentration (LC50) values of 1.2 and 1.1% respectively. Meloidogyne incognita egg hatch was less sensitive to extracts from velvetbean than the juvenile (J2) stage. There was no difference among LC50 values of the extracts from different plant parts against the egg stage. Based on LC50 values, the extract from fine roots was the least toxic to J2 (LC50 39.9%), and the extract from vines the most toxic (LC50 7.8%). The effects of the extracts were nematicidal because LC50 values did not change when the extracts were removed and replaced with water.

Plantago lanceolata and Plantago rugelii Extracts are Toxic to Meloidogyne incognita but not to Certain Microbes.

Extracts from the plants Plantago lanceolata and P. rugelii were evaluated for toxicity to the root-knot nematode Meloidogyne incognita, the beneficial microbes Enterobacter cloacae, Pseudomonas fluorescens and Trichoderma virens, and the plant-pathogenic fungi Fusarium oxysporum f. sp. gladioli, Phytophthora capsici, Pythium ultimum, and Rhizoctonia solani. Wild plants were collected, roots were excised from shoots, and the plant parts were dried and ground to a powder. One set of extracts (10% w/v) was prepared in water and another in methanol. Treatments included extract concentrations of 25%, 50%, 75% and 100%, and water controls. Meloidogyne incognita egg hatch was recorded after 7-day exposure to the treatments, and second-stage juvenile (J2) activity after 48 hours. All extracts were toxic to eggs and J2, with P. lanceolata shoot extract tending to have the most activity against M. incognita. Numbers of active J2 remained the same or decreased in a 24-hour water rinse following the 48-hour extract treatment, indicating that the extracts were lethal. When data from water- and methanol-extracted roots and shoots of both plant species were combined for analysis, J2 tended to be more sensitive than eggs to the toxic compounds at lower concentrations, while the higher concentrations (75% and 100%) were equally toxic to both life stages. The effective concentrations causing 50% reduction (EC(50)) in egg hatch and in J2 viability were 44.4% and 43.7%, respectively. No extract was toxic to any of the bacteria or fungi in our assays.

Effects of geldanamycin on hatching and juvenile motility in Caenorhabditis elegans and Heterodera glycines.

Several Streptomyces species are known to produce metabolites that inhibit plant pathogens. One such compound is geldanamycin (GA), a benzoquinone ansamycin originally isolated from Streptomyces hygroscopicus. We examined the effect of geldanamycin on egg hatch and juvenile motility in Caenorhabditis elegans and in two populations of the plant-parasitic nematode Heterodera glycines. When C. elegans eggs were exposed to geldanamycin, both hatch and motility were reduced by GA doses between 2 and 50 microg/ml. The H. glycines inbred populations TN17 and TN18 exhibited low dose stimulation of hatch and motility, whereas levels occurring at higher GA doses were at or below control levels. These experiments represent the first demonstration of geldanamycin effects in C. elegans and H. glycines and suggest that the heat shock chaperone Hsp90, the known molecular target of geldanamycin, may be involved in nematode egg hatch and motility. This study also indicates that geldanamycin-producing strains of Streptomyces may be useful as biocontrol agents for nematodes.