Differences in activity between infective juveniles (IJ) of the entomopathogenic nematode Steinernema carpocapsae that emerged directly from cadavers onto either a sand or agar substrate compared with those emerging from a cadaver into water and then being placed on the same substrate are known to occur. Differences between S. carpocapsae IJ that emerged directly from a cadaver vs. those that emerged from a cadaver and held in water were further elucidated. Dispersed and non-dispersed IJ from a cadaver were compared with those held in water between two time periods designated as early- (first two days) or late-emerging IJ (seventh day). A significantly greater proportion of early-emerging IJ from the cadaver treatment dispersed, compared with late-emerging IJ from a cadaver or either group of emerging IJ held in aqueous suspension. Moreover, IJ from cadavers were more infectious than those from the aqueous suspensions, and IJ that dispersed were less infectious than those that did not disperse. IJ that emerged early were mostly males, whereas those that emerged late were mostly females. For the non-dispersed IJ, most that emerged early were males, and those that emerged later were females, but among dispersing IJ, there was no difference in sex ratio between early- and late-emerging nematodes.
Ambush forager; foraging behavior; insect-parasitic nematode; Steinernema carpocapsae; Steinernematidae
Root-infecting nematodes are a major cause of white clover, Trifolium repens, not reaching its potential in New Zealand pastures. Resistance and/or tolerance are the preferred control options. Greenhouse-based, recurrent selection programs have developed resistance to Meloidogyne trifoliophila and Heterodera trifolii, and a field-based program has developed tolerance. Lines from these programs were compared with commercial cultivars as controls in a series of field trials at four sites over 4 years. Resistant lines from the CCN program performed better than susceptible lines and as well as most cultivars, reflecting the high level of resistance developed in this greenhouse-based program. In stained root from Cambridge, numbers of CCN were lower in resistant lines than in cultivars; numbers in susceptible lines were intermediate. CCN resistance was also reflected to a lesser extent in the number of cysts counted in soil under resistant lines in Palmerston North. The root-knot nematode-resistant material performed better than the susceptible and as well as most cultivars. In one trial of CRKN-resistant lines, resistant and susceptible lines had similar numbers of CRKN which were both lower than the numbers in the cultivars; in the second trial, there were fewer CRKN in resistant than in susceptible lines or cultivars. The tolerant selections, developed under field conditions, performed as well as or better than the cultivars. The selections from the breeding programmes have exhibited strong agronomic potential across locations and years, and the best material has been crossed; progeny are being assessed in current field trials.
Heterodera trifolii; Meloidogyne trifoliophila; nematode; New Zealand; pasture; resistance; tolerance; Trifolium repens; white clover
A difference in movement has been hypothesized to exist between Caenorhabditis elegans strains lacking one of two main genes for acetylcholinesterase (AChE), ace-1(+) and ace-2(+). We explored the precision of movement as an endpoint by measuring and comparing the movements of these strains (VC505 and GG202, respectively) and of N2 (wild-type). The order of movement of the strains is: N2 > VC505 > GG202; therefore, loss of the ace-2(+) gene is more detrimental to movement. We then compared the sensitivities of the three strains to an AChE inhibitor (propoxur) by generating movement-concentration curves, identifying effective concentrations that decreased movement by 50% (EC50), and comparing them. EC50 show an order of: N2 ≈ GG202 < VC505. Therefore, the enzymes encoded by ace-1(+) were more susceptible to propoxur than those of ace-2(+), suggesting that the innate difference in the AChE classes' contributions to movement will not always determine the strain sensitivity. Measuring movement was sufficiently precise to record differences following genetic manipulation and further chemical exposure.
acetylcholinesterase; behavior; Caenorhabditis elegans; genetics; inhibitor; method; movement; physiology; technique
A PCR-based diagnostic assay was developed for early detection and identification of Aphelenchoides fragariae directly in host plant tissues using the species-specific primers AFragFl and AFragRl that amplify a 169-bp fragment in the internal transcribed spacer (ITS1) region of ribosomal DNA. These species-specific primers did not amplify DNA from Aphelenchoides besseyi or Aphelenchoides ritzemabosi. The PCR assay was sensitive, detecting a single nematode in a background of plant tissue extract. The assay accurately detected A. fragariae in more than 100 naturally infected, ornamental plant samples collected in North Carolina nurseries, garden centers and landscapes, including 50 plant species not previously reported as hosts of Aphelenchoides spp. The detection sensitivity of the PCR-based assay was higher for infected yet asymptomatic plants when compared to the traditional, water extraction method for Aphelenchoides spp. detection. The utility of using NaOH extraction for rapid preparation of total DNA from plant samples infected with A. fragariae was demonstrated.
Aphelenchoides fragariae; detection; diagnosis; foliar nematode; ITS1; method; NaOH; ornamental host; PCR; rDNA
The importance of plant-parasitic nematodes as yield-limiting pathogens of cotton has received increased recognition and attention in the United States in the recent past. This paper summarizes the remarks made during a symposium of the same title that was held in July 2007 at the joint meeting of the Society of Nematologists and the American Phytopathological Society in San Diego, California. Although several cultural practices, including crop rotation, can be effective in suppressing the populations of the important nematode pathogens of cotton, the economic realities of cotton production limit their use. The use of nematicides is also limited by issues of efficacy and economics. There is a need for development of chemistries that will address these limitations. Also needed are systems that would enable precise nematicide application in terms of rate and placement only in areas where nematode population densities warrant application. Substantial progress is being made in the identification, characterization and mapping of loci for resistance to Meloidogyne incognita and Rotylenchulus reniformis. These data will lead to efficient marker-assisted selection systems that will likely result in development and release of nematode-resistant cotton cultivars with superior yield potential and high fiber quality.
Meloidogyne mayaguensis is a damaging root-knot nematode able to reproduce on root-knot nematode-resistant tomato and other economically important crops. In a growth chamber experiment conducted at 22 and 33°C, isolate 1 of M. mayaguensis reproduced at both temperatures on the Mi-1-carrying tomato lines BHN 543 and BHN 585, whereas M. incognita race 4 failed to reproduce at 22°C, but reproduced well at 33°C. These results were confirmed in another experiment at 26 ± 1.8°C, where minimal or no reproduction of M. incognita race 4 was observed on the Mi-1-carrying tomato genotypes BHN 543, BHN 585, BHN 586 and ‘Sanibel’, whereas heavy infection and reproduction of M. mayaguensis isolate 1 occurred on these four genotypes. Seven additional Florida M. mayaguensis isolates also reproduced on resistant ‘Sanibel’ tomato at 26 ± 1.8°C. Isolate 3 was the most virulent, with reproduction factor (Rf) equal to 8.4, and isolate 8 was the least virulent (Rf = 2.1). At 24°C, isolate 1 of M. mayaguensis also reproduced well (Rf ≥ 1) and induced numerous small galls and large egg masses on the roots of root-knot nematode-resistant bell pepper ‘Charleston Belle’ carrying the N gene and on three root-knot nematode-resistant sweet pepper lines (9913/2, SAIS 97.9001 and SAIS 97.9008) carrying the Tabasco gene. In contrast, M. incognita race 4 failed to reproduce or reproduced poorly on these resistant pepper genotypes. The ability of M. mayaguensis isolates to overcome the resistance of tomato and pepper genotypes carrying the Mi-1, N and Tabasco genes limits the use of resistant cultivars to manage this nematode species in infested tomato and pepper fields in Florida.
Capsicum annuum; bell pepper; resistance; root-knot nematodes; Solanum lycopersicum; sweet pepper
The tree Melaleuca quinquenervia invades all types of habitats of South Florida leading to up to 80% loss of aboveground diversity. To examine impacts on the belowground ecosystem, we investigated the composition and diversity of nematodes from soils dominated by the invasive tree and compared them with soils supporting native plant communities at six locations across the Florida Everglades over three years. Despite the significant differences in soil type, hydrology, and native plant composition of the sites, there were consistent differences in nematode communities between soil environments under the native and invaded plant communities. The total abundance and diversity of nematodes in soils dominated by M. quinquenervia was 60% and 80% of adjacent soils under native plants. Fungal-feeding and plant-parasitic nematodes were twice as abundant under native plants as under M. quinquenervia. Nematode communities under M. quinquenervia were bacterivore-dominated, while under native vegetation plant-parasite dominated. The overall diversity of nematodes was 20% lower under the exotic than under native plants, with plant parasites being 36% and fungivores being 30% less diverse. Soil moisture, % of Ca, Mg, and clay particles and total soil C and N were greater in M. quinquenervia soils, but plant-available concentrations of P, K, Ca, and Mg as well as CEC were reduced. Overall, data suggests that the invasion process may modify soil biotic and abiotic conditions that in turn promote the advancement of the exotic M. quinquenervia and displacement of the native plants.
diversity; ecology; enemy release; exotic plant; Florida Everglades; invasive; Melaleuca quinquenervia; nematode community; nematode diversity; plant-soil feedback; soil chemistry
Twenty-four weeds commonly found in commercial potato fields in Quebec were evaluated for their host suitability to the root-lesion nematode, Pratylenchus penetrans, under greenhouse conditions. Brown mustard (Brassica juncea) and rye (Secale cereale) were included as susceptible controls and forage pearl millet hyb. CFPM 101 (Pennisetum glaucum) as a poor host. Pratylenchus penetrans multiplied well on 22 of the 24 weed species tested (Pf/Pi ≥ rye or brown mustard). Cirsium arvense, Leucanthemum vulgare and Matricaria discoida were classified as very good hosts with a Pf/Pi ranging from 1.60 to 2.54, while Ambrosia artemisiifolia and Cyperus esculentus were classified as poor hosts with a Pf/Pi from 0.01 to 0.15. Amaranthus powellii, A. retrqflexus, Raphanus raphanistrum, Rorippa palustris, Cerastium fontanum, Spergula arvensis, Stellaria media, Chenopodium album, Vicia cracca, Elytrigia repens, Digitaria ischaemum, Echinochloa crusgalli, Panicum capillare, Setaria faberii, S. pumila, S. viridis, Polygonum convolvulus, P. scabrum and P. persicaria were intermediate hosts with Pf/Pi values ranging from 0.33 to 2.01. The plant species and the botanical family had a significant impact on nematode reproduction. The Brassicaceae family resulted in the greatest reproduction of P. penetrans, and the Cyperaceae resulted in the least. The plant life-cycle (annual vs. perennial) had no impact on nematode population.
brown mustard; host range; pearl millet; potato; Pratylenchus penetrans; root-lesion nematode; rye; weed
A method to establish two experimental corky ringspot disease (CRS) plots that had no prior CRS history is described. CRS is a serious disease of potato in the Pacific Northwest caused by tobacco rattle virus (TRV) and transmitted primarily by Paratrichodorus allius. ‘Samsun NN’ tobacco seedlings were inoculated with viruliferous P. allius in the greenhouse before they were transplanted into the field soil at the rate of 3,000 plus seedlings/ha. Care was taken to keep soil around plants in the greenhouse and transplants in the field moist to avoid vector mortality. The vector population in the soil of one of the fields was monitored by extraction, examination under microscope and bioassay on tobacco seedlings to ascertain that they were virus carriers. Presence of virus in tobacco bioassay plants was determined by visual symptoms on tobacco leaves and by testing leaves and roots using ELISA. Although TRV transmission was rapid, there was loss of infectivity in the first winter which necessitated a re-inoculation. After two years of planting infected tobacco seedlings, 100% of soil samples collected from this field contained viruliferous P. allius. In the second field, all five commercial potato cultivars, known to be susceptible, expressed symptoms of CRS disease indicating that the procedure was successful.
method; Paratrichodorus allius; potato; Solatium tuberosum; tobacco rattle virus
Some studies suggest that entomopathogenic nematodes (EPN) affect plant-parasitic nematode populations. Here, the effects of live and dead IJ of Heterorhabditis bacteriophora JPM4, H. baujardi LPP7, Steinernema feltiae SN and S. carpocapsae All were evaluated against eggs and J2 of the plant-parasitic nematode Meloidogyne mayaguensis. According to treatment, 100 IJ were applied with 350 eggs, 350 J2 or 175 eggs + 175 J2 to tomato plants. Bioassays were conducted in March to May and repeated in September to November 2005. Both experiments lasted 9 weeks, and the variable evaluated was number of galls per plant. When eggs were used for infections in the first trial, plants exhibited lower gall number compared to control when live and dead H. baujardi IJ and live S. feltiae IJ were added (9.7, 4.5, 7.3 and 85.7 galls, respectively). In the second trial, live S. feltiae and S. carpocapasae IJ influenced gall formation compared to control (14.33, 14.57 and 168.02 galls, respectively). When J2 were used for infections, plants with live H. baujardi IJ presented less galls when compared to control in both trials (38.3 and 355.7 galls in the first trial and 145.2 and 326.2 in the second one, respectively). Infection with a mixture of J2 and eggs resulted in fewer galls than when live S. feltiae IJ were present in both trials, compared to control (38.3 and 44.2 galls vs. 275.3 and 192.2 galls, respectively). We conclude that H. baujardi and S. feltiae apparently may be inhibiting egg hatching and J2 infection.
Entomopathogenic nematodes; nematode-nematode interaction; biological control; plant-parasitic nematode; Meloidogyne mayaguensis
Polianthes tuberosa is a commercially valuable flower crop in the Mekong Delta of Vietnam that is propagated by the harvesting and planting of bulbs. The cultivation of P. tuberosa is complicated by an endemic nematode infection that damages a high proportion of the plants. Based on morphological criteria and ribosomal RNA gene sequencing, we have determined that the infection is caused by an Aphelenchoides sp. nematode and is most likely Aphelenchoides besseyi. By scoring various parts of harvested plants with flowers for the presence of viable nematodes over a period of six months, we determined that the nematode is an ectoparasite that can survive the intercrop periods, especially in the bulbs that are used to plant new crops. A comparison of farming practices in the Mekong Delta failed to identify useful control methods, but rather indicated that fields that have cultivated P. tuberosa for the longest periods suffer the worst damage from the nematode infection. Finally, we demonstrated that the nematode is capable of infecting 30 rice cultivars but does not cause the white tip disease usually associated with A. besseyi infection.
Aphelenchoides besseyi; biological control; host-parasitic relationship; Mekong Delta; plant disease loss; Polianthes tuberosa; rRNA sequence; survival; Vietnam
Pseudomonas fluorescens GcM5-1A, isolated from the pine wood nematode (PWN), Bursaphelenchus xylophilus, was cultured in Luria Broth medium (LB). The clarified culture was extracted with ethyl acetate, and two dipeptides were purified from the extract. The chemical structures of 1 and 2 were identified as cyclo(-Pro-Val-)and cyclo(-Pro-Tyr-), respectively, by MS, 1H NMR, 13C NMR,1H-1H COSY, 1H -13C COSY spectra. Bioassay results showed that the two compounds were toxic to both suspension cells and seedlings of Pinus thunbergii, which may offer some clues to research the mechanism of pine wilt disease caused by PWN.
Bursaphelenchus xylophilus; cyclo(-Pro-Tyr-); cyclo(-Pro-Val-); interaction; Pinus thunbergii; Pseudomonas fluorescens GcM5-1A; toxicity
The toxic and propagation effects on Bursaphelenchus xylophilus of 28 Thymus vulgaris red oil and white oil compounds were examined using direct contact and cotton ball bioassays. Results were compared with those of the trunk-injection nematicides emmamectin benzoate, levamisol hydrochloride and morantel tartrate. In direct contact bioassays, geraniol (LC50, 0.47 mg/ml) was the most toxic compound, followed by thymol (1.08 mg/ml), carvacrol (1.23 mg/ml) and terpinen-4-ol (2.61 mg/ml). In cotton ball tests with 20 inactive compounds at 2 mg/cotton ball, p-cymene significantly inhibited propagation (propagation ratio [PR] 8), compared with the castor oil-ethanol-treated control (PR 56). Propagation stimulation was observed with (–)-caryophyllene oxide, (+)-ledene, (+)- and (–)-limonene, linalool oxide, β-myrcene, (–)-α-phellandrene, (+)-α-pinene and γ-terpinene (PR 63–100). The other 10 compounds exhibited low to moderate levels of propagation inhibition (PR 36–56). At 0.1 μg/cotton ball, emmamectin benzoate and morantel tartrate exhibited complete suppression of propagation, whereas a very low level of propagation inhibition was obtained from levamisol hydrochloride (PR 6). In conclusion, propagation-stimulating compounds can exist in plants in addition to nematicidal compounds, and careful use of plant preparations containing high quantities of these compounds is mandatory.
Bursaphelenchus xylophilus; pine wood nematode; botanical nematicide; propagation stimulation; propagation inhibition; essential oil; Thymus vulgaris
Naturally occurring disease-suppressive soils have been documented in a variety of cropping systems, and in many instances the biological attributes contributing to suppressiveness have been identified. While these studies have often yielded an understanding of operative mechanisms leading to the suppressive state, significant difficulty has been realized in the transfer of this knowledge into achieving effective field-level disease control. Early efforts focused on the inundative application of individual or mixtures of microbial strains recovered from these systems and known to function in specific soil suppressiveness. However, the introduction of biological agents into non-native soil ecosystems typically yielded inconsistent levels of disease control. Of late, greater emphasis has been placed on manipulation of the cropping system to manage resident beneficial rhizosphere microorganisms as a means to suppress soilborne plant pathogens. One such strategy is the cropping of specific plant species or genotypes or the application of soil amendments with the goal of selectively enhancing disease-suppressive rhizobacteria communities. This approach has been utilized in a system attempting to employ biological elements resident to orchard ecosystems as a means to control the biologically complex phenomenon termed apple replant disease. Cropping of wheat in apple orchard soils prior to re-planting the site to apple provided control of the fungal pathogen Rhizoctonia solani AG-5. Disease control was elicited in a wheat cultivar-specific manner and functioned through transformation of the fluorescent pseudomonad population colonizing the rhizosphere of apple. Wheat cultivars that induced disease suppression enhanced populations of specific fluorescent pseudomonad genotypes with antagonistic activity toward R. solani AG-5, but cultivars that did not elicit a disease-suppressive soil did not modify the antagonistic capacity of this bacterial community. Alternatively, brassicaceae seed meal amendments were utilized to develop soil suppressiveness toward R. solani. Suppression of Rhizoctonia root rot in response to seed meal amendment required the activity of the resident soil microbiota and was associated with elevated populations of Streptomyces spp. recovered from the apple rhizosphere. Application of individual Streptomyces spp. to soil systems provided control of R. solani to a level and in a manner equivalent to that obtained with the seed meal amendment. These and other examples suggest that management of resident plant-beneficial rhizobacteria may be a viable method for control of specific soilborne plant pathogens.
suppressive soils; biological control; replant disease; rhizobacteria
Thirty-three isolates of root-knot nematode were recovered from soil samples from rice-wheat fields in Nepal and maintained on rice cv. BR 11. The isolates were characterized using morphology, host range and DNA sequence analyses in order to ascertain their identity. Results indicated phenotypic similarity (juvenile measurements, perennial pattern, host range and gall shape) of the Nepalese isolates with Meloidogyne graminicola, with minor variations. The rice varieties LA 110 and Labelle were susceptible to all of the Nepalese isolates, but differences in the aggressiveness of the isolates were observed. Phylogenetic analyses based on the sequences of partial internal transcribed spacer (ITS) of the rRNA genes indicated that all Nepalese isolates formed a distinct clade with known isolates of M. graminicola with high bootstrap support. Furthermore, two groups were identified within the M. graminicola clade. No correlation between ITS haplotype and aggressiveness or host range was found among the tested isolates.
Meloidogyne graminicola; morphology; nucleotide polymorphism; Oryza sativa; phylogeny; root-knot nematode; systematics; virulence
Commercial plant essential oils from 26 plant species were tested for their nematicidal activities against the pinewood nematode, Bursaphelenchus xylophilus. Good nematicidal activity against B. xylophilus was achieved with essential oils of ajowan (Trachyspermum ammi), allspice (Pimenta dioica) and litsea (Litsea cubeba). Analysis by gas chromatography-mass spectrometry led to identification of 12, 6 and 16 major compounds from ajowan, allspice and litsea oils, respectively. These compounds from three plant essential oils were tested individually for their nematicidal activities against the pinewood nematode. LC50 values of geranial, isoeugenol, methyl isoeugenol, eugenol, methyl eugenol and neral against pine wood nematodes were 0.120, 0.200, 0.210, 0.480, 0.517 and 0.525 mg/ml, respectively. The essential oils described herein merit further study as potential nematicides against the pinewood nematode.
ajowan; allspice; litsea; nematicidal activity; pine wood nematode; plant essential oils
The identity and taxonomy of the genus Crassolabium are discussed based on examination of material of C. australe, its type species and its comparison with Iberian species of close genera. The existence of refractive masses (thickenings) at the inner core of lateral lips, the most distinctive diagnostic feature of Crassolabium, is considered to be of minor taxonomical significance because of its interspecific and even intraspecific variability. It is concluded that Crassolabium and Thonus are identical, and a reversal of precedence among both genera is suggested. Crassolabium australe is re-described, and some comments are provided on C. robustum, the second species in the genus.
Crassolabium australe; Crassolabium robustum; morphology; synonymy; taxonomy; Thonus
A new species of the genus Protorhabditis is described from natural areas in the SE Iberian Peninsula. Protorhabditis spiculocrestata sp. n. is distinguished by its body length 387–707 μm in females and 375–546 μm in males, lip very low and flattened, stoma 14–22 μm long, female tail conical-elongate (48–100 μm, c = 6.4–8.3, c′ = 4.8–7.5), phasmid near anus, male tail conical (20–27 μm, c = 18.3–22.3, c′ = 1.4–1.5), bursa peloderan closed anteriorly and bears eight papillae (1+2+1+1+3), spicules 23–26 μm long, and gubernaculum 10–16 μm long. Diploscapter coronatus is also presented. Description, measurements and illustrations, including SEM photographs, are provided. A key to species of Protorhabditis is also given as well a compendium of their measurements.
description; Diploscapter; key; morphology; new species; Protorhabditis; Rhabditids; SE Spain; SEM; taxonomy
Corky ringspot disease (CRS) of potato produces necrotic areas in tubers that are considered quality defects that can lead to crop rejection. CRS is caused by tobacco rattle virus that is vectored by stubby-root nematodes (Paratrichodorus spp., Trichodorus spp.) at very low population densities, making disease management difficult and expensive. Fumigation with metam sodium (MS) is a common practice to control soil-borne fungi and increase potato yield. MS is generally applied in water via chemigation (water-run, WR) but is ineffective at controlling CRS when WR-applied, even at high rates. Therefore, WR MS is often used in combination with 1,3-dichloropropene (1,3-D), aldicarb or oxamyl to attain adequate CRS control. Between 1996 and 2000, fields with a history of CRS were treated with WR MS, shank-injected MS, and/or 1,3-D, and tubers were evaluated for symptoms of CRS. Shank injection of MS (SH MS) at depths of 41 cm, 15 and 30 cm, or 15, 30 and 45 cm controlled CRS over 3 years of testing. All rates of 280 liters/ha or greater were effective. Shank injection of metam potassium (MP) at rates of 448 liters/ha was also effective. 1,3-D controlled CRS alone or in combination with WR or SH MS. Proper shank application of MS or MP may adequately control CRS without the additional cost of other nematicides at low (<10 P. allius/250 g soil) to moderate (10 to 30 P. allius/250 g soil) populations of the nematode vector. Although SH MS was superior to WR MS, additional research is necessary to determine if this practice would be sufficient at higher CRS disease pressure or if addition of other nematicides would be necessary.
1,3-dichloropropene; corky ringspot; CRS; fumigants; metam potassium; metam sodium; nematicides; Paratrichodorus allius; potato; stubby-root nematode; tobacco rattle virus; TRV
Aminopeptidase was detected in homogenates of the free-living nematode Panagrellus redivivus with the aminoacyl substrate L-alanine-4-nitroanilide. Subcellular distribution of activity was 80% soluble and 20% membrane-associated. Aminopeptidases in the two fractions differed in affinity for Ala-4-NA, with Km's of 0.65 mM (soluble) and 2.90 mM (membrane). Specific activities (units/mg) at pH 7.8, 27°C were 9.10 (soluble) and 14.30 (membrane). Each enzyme was competitively inhibited by amastatin (90% at 100 μM inhibitor, IC50 = 3.7 μM) and inhibited by puromycin (30% at 500 μM) and 1,10-phenanthroline (IC50's:; 148 μM, soluble; 89 μM, membrane). Activity was restored by Zn++, with maximum recoveries of 50% (soluble) and 90% (membrane), each at 23 μM ZnCl2. Estimated molecular masses for each were ∼150 kDa. FMRFamide-like neuropeptides behaved as competitive inhibitors. Modification of the N-terminal F of FMRFamide weakened inhibition by 95%, suggesting that the N-terminus is essential for binding to the enzyme. Two nematode FMRFamides, APKPFIRFa and RNKFEFIRFa, were the most potent tested. This is the first biochemical characterization of aminopeptidase in a free-living nematode other than Caenorhabditis elegans and demonstrates the high selectivity of the P. redivivus enzymes for neuropeptide substrates.
FMRFamide-like peptide; inhibitor; membrane; metallopeptidase; neuropeptide; protease
Use of resistant cultivars is a desirable approach to manage the peanut root-knot nematode (Meloidogyne arenaria). To incorporate resistance into commercially acceptable cultivars requires reliable, efficient screening methods. To optimize the resistance screening protocol, a series of greenhouse tests were done using seven genotypes with three levels of resistance to M. arenaria. The three resistance levels could be separated based on gall indices as early as two weeks after inoculation (WAI) using 8,000 eggs of M. arenaria per plant, while four or more weeks were needed when 1,000–6,000 eggs/plant were used. High inoculum densities (over 8,000 eggs/plant) were needed to separate the three resistance levels based on eggs per gram of root within eight WAI. A gall index based on percentage of galled roots could separate the three resistance levels at lower inoculum levels and earlier harvest dates than other assessment methods. The use of eggs vs. second-stage juveniles (J2) as inoculum provided similar results; however, it took three to five more days to collect J2 than to collect eggs from roots. Plant age affected gall index and nematode reproduction on peanut, especially on the susceptible genotypes AT201 and D098. The genotypes were separated into their correct resistance classes when inoculated 10 to 30 days after planting, but were not separated correctly when inoculated on day 40.
Arachis hypogaea; assessment date; host-plant resistance; inoculation date; inoculum level; inoculum type; Meloidogyne arenaria; method; peanut; resistance evaluation; root-knot nematode
Laboratory experiments were conducted to study non-target effects of augmenting entomopathogenic nematode (EPN)communities in soil. When raw soil from a citrus orchard was augmented with either 2,000 Steinernema riobrave or S. diaprepesi, fewer EPN (P ≤ 0.05) survived if the soil had also been treated with 2,000 S. riobrave 7 d earlier (i.e., two augmentation events rather than one). EPN survival was unaffected by treatment (P ≤ 0.05) in soil that was air-dried to disrupt antagonist activity prior to the experiment. When S. diaprepesi, S. riobrave, Heterorhabditis zealandica or no EPN were added to raw soil and S. diaprepesi was added 5 d later, the survival of both S. diaprepesi and of total EPN was greater (P ≤ 0.05) in soil that received no pretreatment than in soilpre treated with S. riobrave. Pretreatment of soil with H. zealandica or S. diaprepesi had less or no affect on survival of S. diaprepesi or total EPN. When nematodes were recovered from soil and placed on water agar, the number of S. diaprepesi that were killed by endoparasitic and trapping nematophagous fungi was greater (P ≤ 0.05) if soil was pretreated with steinernematid species than if the soil was not pretreated or was pretreated with H. zealandica. The adverse effects of pretreating soil on EPN survival were density dependent within a range of pretreatment dosages (20–100 IJ/cm2 soil surface), and the treatment effects required more time to become evident at lower than at higher dosages. These experiments suggest that non-target effects of augmenting the EPN community in soil vary among EPN species and have the potential to temporarily reduce EPN numbers below the natural equilibrium density.
Antagonism; nematophagous fungi; numerical response; post-application biology; predation; survival