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Supplemental description of Paraphelenchus acontioides (Tylenchida: Aphelenchidae, Paraphelenchinae), with ribosomal DNA trees and a morphometric compendium of female Paraphelenchus
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Nematodes were isolated from surface-sterilised stems of cheatgrass, Bromus tectorum (Poaceae), in Colorado, grown on Fusarium (Hypocreaceae) fungus culture, and identified as Paraphelenchus acontioides. Morphometrics and micrographic morphology of this species are given to supplement the original description and expand the comparative species diagnosis. A tabular morphometric compendium of the females of the 23 species of Paraphelenchus is provided as the last diagnostic compilation was in 1984. Variations in the oviduct within the genus are reviewed to evaluate the taxonomic assignment of P. deckeri, a morphologically transitional species between Aphelenchus and Paraphelenchus. Sequences were generated for both 18S and 28S ribosomal DNA, representing the first identified species within Paraphelenchus so characterised. These sequences were incorporated into phylogenetic trees with related species of Aphelenchidae and Tylenchidae. Aphelenchus avenae isolates formed a well supported monophyletic sister group to Paraphelenchus. The ecology of Paraphelenchus, cheat grass and Fusarium is also discussed.
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A microcosm experiment on the effects of permethrin on a free-living nematode assemblage
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Microcosms were used to assess the impact of permethrin on the abundance and diversity of free-living marine nematodes. The nematodes were exposed to three permethrin concentrations (50, 100 and 150 μg l−1), and the effects were examined after 25 days. The abundances of nematodes at all permethrin concentrations significantly exceeded those in the controls. Multivariate analyses demonstrated that responses of nematode species to permethrin treatments were varied: Pselionema sp., Prochromadorella neapolitana and Spirinia gerlachi were eliminated at the low dose and seemed to be species intolerant to permethrin; Trichotheristus mirabilis and Xyala striata, which increased with increasing contamination levels, seemed to be ‘opportunistic’ and/or ‘resistant’ species. Results showed significant differences between univariate measures of diversity of control nematodes and those from permethrin-contaminated microcosms, where all decreased significantly with increasing abundance of the most tolerant species to permethrin. The use of microcosms has allowed the effects of permethrin on nematodes to be assessed individually, which is not possible in the field.
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Studies on the genus Aporcelaimellus Heyns, 1965 (Dorylaimida: Aporcelaimidae). An interesting new species from Western Africa
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Aporcelaimellus porosus sp. n., collected in rice fields from Guinea and Ivory Coast, is described and illustrated. The new species is characterised by its body length of 2.51-2.81 mm, numerous, particularly conspicuous ventral body pores, lip region offset by constriction and 19.5-21.5 μm broad, odontostyle 26-30 μm long with its ventral side distinctly thickened at its anterior portion and aperture occupying 64-70% of its length, neck 589-626 μm long, pharyngeal expansion 305-332 μm long or 50-55% of total neck length, uterus tripartite and 287-446 μm long or 3.5-5.5 times the corresponding body diam., pars refringens vaginae with two well developed sclerotised pieces, vulva transverse (V=52-56), tail short and rounded (25-33 μm, c=84-103, c'=0.5-0.7), spicules 81-87 μm long, and eight spaced ventromedian supplements which lack a hiatus. It is compared in detail with its closest congeners.
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Cover crops and Pochonia chlamydosporia for the control of Meloidogyne javanica
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The objective of this research was to evaluate the effect of the combination of Pochonia chlamydosporia var. chlamydosporia with summer and winter cover plants on the control of Meloidogyne javanica on tomato plants under glasshouse conditions. Treatment combinations were with four soil covers (pearl millet and Surinam grass in Experiment 1, oil radish and black oat in Experiment 2; plus tomato and fallow controls) and two P. chlamydosporia treatments (with or without the fungus). The antagonist was applied to nematode-infested soil when the cover crops or tomato were planted. Tomato plants were removed and the above-ground parts of the cover crops were cut, dried, and placed on the pots 60 days after planting. One tomato seedling was transplanted in each pot in a no-tillage system and cultivated for 60 days. Surinam grass, pearl millet and black oat reduced galls and eggs of M. javanica by more than 90%, without application of the fungus. However, P. chlamydosporia + Surinam grass significantly reduced by 72% the number of galls compared with cultivation of the grass in soil without the fungus. Pochonia chlamydosporia became established in soil and could be re-isolated at the end of both experiments. Colony forming units (CFU) (g soil)–1 varied from 1.0 × 105 (fallow) to 2.6 × 105 (pearl millet) and from 1.1 × 105 (fallow) to 2.3 × 105 (oil radish) for the experiments with summer soil cover crops and winter soil cover crops, respectively. The cultivation of Surinam grass, pearl millet and black oat reduced M. javanica populations, and the combination with P. chlamydosporia may favour the establishment of the fungus in the soil and enhance the control of the nematode.
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Description of Rhyssocolpus vinciguerrae sp. n. (Dorylaimida, Nordiidae) from Iran and the first molecular study of this genus
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Rhyssocolpus vinciguerrae sp. n., from natural habitats in Iran, is described, illustrated and sequenced. It is characterised by the body length of 1.04-1.37 mm, lip region offset by depression and 11-13 μm broad, odontostyle 8-10 μm or 0.7-0.8 times the lip region diam. long, neck 227-265 μm long, pharyngeal expansion 80-95 μm long or 31-35% of total neck length, a dorsal cell mass present between cardia and the end of the anterior ovary/testis, uterus bipartite, 90-170 μm long, vulva longitudinal (V = 48-55), abundant irregularities in body cuticle around vulva, female tail conical with rounded terminus (35-55 μm, c = 24-34, c′ = 1.4-1.9), spicules 43-51 μm long and 6-8 spaced ventromedian supplements located outside the range of the spicules. It is very similar to R. aquilonius, R. arcticus and R. iuventutis. A molecular characterisation of the new species was done on ribosomal DNA nearfull-length small subunit 18S gene, internal transcribed spacer and partial 5.8S gene. The results obtained support a close relationship between Rhyssocolpus and Heterodorus, and a more distant relationship with Enchodelus.
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Effect of the Mi gene on reproduction of Meloidogyne hispanica on tomato genotypes
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The root-knot nematode resistance (Mi) gene was screened in 25 tomato genotypes of Solanum lycopersicum, by amplification of REX-1 and Mi23 markers. Ten heterozygous tomato genotypes (Mimi), nine homozygous (MiMi) at the Mi locus and six lacking the Mi gene for resistance to root-knot nematode were identified using the marker REX-1. The results obtained with Mi23 marker confirmed the Mi gene status of the tomato genotypes, except for genotype Valouro RZ F1 that was homozygous (MiMi) and heterozygous (Mimi) at the Mi locus when using the REX-1 and Mi23 markers, respectively. The pathogenicity of Meloidogyne hispanica on the 25 tomato genotypes was assessed 60 days after inoculation with 5000 eggs on the basis of root gall index (GI) and reproduction factor (Rf). All the tomato genotypes were susceptible (excellent or good hosts), with GI>4 and Rf>2, except the genotype Rapit (Mimi), considered as resistant/hypersensitive (poor host). In this genotype, the nematode induced galls (GI=4) on its roots and a small number of eggs were produced (Pf=3085±485). Significant differences in reproduction were detected between the Mi allelic conditions and genotypes within Mi allelic conditions. The increasing number of Mi alleles (0, 1 or 2) is associated with decreasing Rf, which suggests a possible dosage effect of the Mi gene. The variability observed in the Rf values for MiMi tomato genotypes may reflect an influence of the genetic background of the plants containing the Mi gene. Ten of the 25 tomato genotypes with Mi gene are commercially available. However, only Rapit can be used to control the three most common Meloidogyne spp. and inhibit the increasing of M. hispanica populations, and may have potential to be included in an integrated pest management programme. However, it is advisable to evaluate the pathogenicity of local populations of this nematode species associated with different environmental factors.
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Molecular and morphological characterisations of two new species of Rotylenchus (Nematoda: Hoplolaimidae) from Iran
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Two new amphimictic species, Rotylenchus iranicus n. sp. and R. conicaudatus n. sp., are described. Rotylenchus iranicus n. sp. is characterised mainly by an offset hemispherical lip region with 5-6, rarely 7, annuli, stylet 39-44 μm long, vulva located at 53-65% and rounded tail with 4-9 annuli and typical smooth tip. Morphologically this species is related to R. montanus, R. provincialis and R. aqualamus. Rotylenchus conicaudatus n. sp. is characterised mainly by a slightly offset conoid-rounded lip region with four or five, rarely six annuli, stylet 27-32 μm long, vulva located at 52-63% and conoid-rounded tail with 10-16 annuli and a typical annulated tip. Morphologically this species is related to R. pumilus, R. abnormecaudatus, R. acuspicaudatus and R. provincialis. The results of the phylogenetic analysis based on sequences of the D2-D3 expansion regions of 28S and ITS1-rRNA genes confirmed the species differentiation. Phylogenetic relationships with other species were difficult to assign using D2-D3 expansion regions of 28S. However, using ITS1-rRNA, R. conicaudatus n. sp. presented a close relationship with R. unisexus, whilst R. iranicus n. sp. was closely related to R. conicaudatus n. sp., R. unisexus, R. incultus and R. laurentinus.
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Effect of the green manures Sinapis alba, Brassica napus and Raphanus sativus on hatching of Globodera rostochiensis
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The potato cyst nematode, Globodera rostochiensis, is a quarantine organism. Environmentally benign control measures for this economically important pest are needed. Green manures, in particular plants from the Brassicaceae, suppress some plant-parasitic nematodes and have potential as control agents. This study examined if growing and incorporating cover crops from the Brassicaceae family influenced hatching of G. rostochiensis. The effect of root diffusates and plant extracts, as well as soil incorporation of plant material from three commonly used species of green manures, was studied in in vitro bioassays and pot tests. The results showed that brassica diffusates and plant extracts were not nematicidal. In addition, although they did not cause hatch by themselves, pretreatment with these solutions enhanced subsequent hatch in host root diffusates. The results are discussed in the context of the hatching response of G. rostochiensis and the likely influence on field usage of these green manures.
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Low temperature survival of post-eclosion stages of the potato rot nematode Ditylenchus destructor Thorne (Tylenchida: Anguinidae)
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The potato rot nematode, Ditylenchus destructor, may experience extreme environmental stress caused by freezing temperatures when overwintering in the field. A series of laboratory experiments were conducted in order to clarify overwintering strategies of the nematode. The current study aimed to examine the cold tolerance of this species in various aqueous environments as well as in plant tissues in order to determine its ability to survive 24 h exposure to subzero temperatures. Cold tolerance of adults and fourth-stage juveniles was significantly lower than that of younger juveniles. The lower lethal temperature of adults was −15°C. Although external ice formation affects all life stages, a few second-stage juveniles were able to survive temperatures as low as −30°C. The results expand the current understanding of freezing survival in the potato rot nematode and will lead to better comprehension of its ability to withstand subzero temperature conditions.
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The effect of temperature on hatch and activity of second-stage juveniles of the root-knot nematode, Meloidogyne minor, an emerging pest in north-west Europe
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Meloidogyne minor is a serious threat to turfgrass in north-west Europe, and has a broad host range that includes other economically important plants. The species was described only recently and little is known about its biology. This study examines the effect of temperature on hatch and motility of second-stage juveniles (J2), and records hatching from egg masses collected from golf greens in different seasons. Eggs were present throughout the year and a high percentage hatch (46-88%) was recorded when they were incubated at 20°C. When egg masses were incubated at constant temperatures, J2 hatched between 15 and 25°C, with limited hatch (<1%) at 10 and 30°C. The percentage hatch was lower at 15°C (43%) than at 20-25°C (63-76%). J2 hatched fastest at 23°C, with an average duration to hatching of 7 days compared to 17 days at 15°C. The range of temperatures at which J2 was active was broader than that at which they hatched. J2 were active from 4-30°C, with greatest activity between 15 and 25°C. The addition of grass root extract temporarily increased J2 activity at 10-20°C, but not at lower temperatures.
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Grassland management history affects the response of the nematode community to changes in above-ground grazing regime
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Changes in grassland management induce disturbances that influence both soil functioning and soil fauna. This study aimed at determining the extent to which the composition of a grassland soil nematode community could be altered by a shift of grazing regime and the potential feedback that these alterations could provoke on grassland functioning. Therefore, we monitored the composition of the soil nematode community (i.e., plant-, bacterial- and fungal-feeders, omnivores and carnivores) of mesocosms that were sampled from two contrasted long-term field trials (high vs low grazing treatments) and subsequently subjected to high or no grazing for 2 years. The soil nematofauna responded faster and more strongly to the application of an intensive grazing regime on a previously extensively exploited system than the other way round. The application of an intensive grazing regime induced a significant increase in numbers of bacterial feeders and a decrease of the relative abundance of fungal-feeding nematodes. The nematofaunal community structure was determined by both the past and current grazing regimes throughout the 2 years of monitoring. Observed effects on soil microbivores seemed to reflect the ‘immediate’ above-ground primary production potential and to follow micro-organism dynamics. On the other hand, observed effects on root-feeding nematodes seemed to reflect the integral effect of past and current grazing regimes on plant community root biomass and quality.
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Tribute to John Horatio O'Bannon (1926-2011)
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Harry Wallace – a thinker who inspired generations of nematologists
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