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In glasshouses practising monoculture of butterhead lettuce in Belgium, high densities of pin nematodes (Paratylenchusspp.) are frequently associated with reduced plant growth. Growers currently apply chemical soil disinfestation measures to manage this problem, although stricter phytosanitary regulations are forcing a shift towards integrated management. Efficient implementation of such management requires knowledge about the factors influencing nematode population dynamics, and the damage threshold for lettuce. The nematode populations in five Belgian glasshouses were monitored for at least 1 year by frequently soil sampling at 0-30 cm and 30-60 cm depth. An undescribed species of Paratylenchuswas identified in all glasshouses based on morphological and molecular features. High nematode densities (>20,000 (100 ml soil)(-1)) occurred in winter and spring. Chemical soil disinfestation lowered these populations greatly, although up to 14% survived in the deeper soil layer. After soil steaming under negative pressure, no pin nematodes were found. After 2 months of black fallow pin nematode densities were reduced by 50%-76%. Lamb's lettuce, parsley and wild rocket were found to be poor hosts in a pot experiment, while reproduction factors (P-f/P-i) on lettuce cultivars varied between 1 and 3. In three experiments with butterhead lettuce 'Cosmopolia' in pots with a series of 9 or 10 densities of Paratylenchussp. [up to 35,000 (100 ml soil)(-1)], no damage to lettuce heads was observed. However, root weight and root quality were reduced, and the corresponding damage thresholds were rather low [1,754 and 362Paratylenchussp. (100 ml soil)(-1), respectively]. Management strategies such as crop rotation, soil disinfestation or fallow are recommended to avoid pin nematode population build-up.

Summary The root-lesion nematode, Pratylenchus penetrans, causes growth reduction in glasshouse-grown lettuce and is mainly controlled by chemical soil disinfestation. Integrated management strategies require more knowledge about the population dynamics and damage threshold densities. We monitored the population during 2.5 years in a commercial glasshouse by sampling soil in the same four 1 m2 spots at 0-30 cm and 30-60 cm depth. The grower grew lettuce in rotation with leek, applied 1,3-dichloropropene in summer and left the field fallow during winter. Growing leek reduced the nematode population slightly but chemical soil disinfestation lowered the numbers drastically, although 41% of the nematodes in the deeper layer survived. Black fallow resulted in a slight increase of the population, probably due to hatching. Two pot experiments with ten densities of P. penetrans were conducted to estimate the damage threshold for a summer and autumn cultivar (‘Cosmopolia’ and ‘Brighton’, respectively). The thresholds for lettuce weight were 669 and 3834 P. penetrans (100 ml soil)−1 in summer and autumn, respectively, but with considerable variability in estimated parameters. The thresholds for root damage were much lower: 204 and 48 P. penetrans (100 ml soil)−1. Nematode numbers did not increase on lettuce in the pot tests (maximum multiplication rate was 0.40) but increased slightly in the commercial setting. These results show that populations of P. penetrans build up slowly when butterhead lettuce is rotated with leek and fallow, but chemical soil disinfestation is required to avoid numbers resulting in root damage.

The restoration of Nardus grasslands is often hampered by high bioavailability of soil phosphorus and disturbed soil communities. In order to better understand these bottlenecks, we studied Nardus grassland species grown together in communities with fast-growing species in 50-liter pots along a gradient of bioavailable phosphorus with or without inoculated soil biota. These mesocosms allowed the plants to freely interact, including competition for light and nutrients. We investigated changes in the plant community composition along the phosphorus gradient using Threshold Indicator Taxa Analysis (TITAN). We found a negative threshold of 11.5 mg POlsen kg−1 with six significant indicator plant species. Above the threshold, a small increase in phosphorus resulted in a disproportionally large drop in biomass for the indicator species, including four typical Nardus grassland species. The decline in these ‘oligotrophic indicator species’ was also linked to increasing plant community biomass, so we suggest the oligotrophic indicator species to be outcompeted for light by fast-growing plant species. We did not find an effect of the soil biota treatment on the biomass of the oligotrophic indicator species, but did observe a positive effect of inoculation with soil biota on the total biomass of the plant community. Interestingly, the threshold for the plant communities in the mesocosm experiment was comparable to the upper bioavailable phosphorus concentrations in remnant Nardus grasslands in northern Belgium. For the restoration of Nardus grasslands, such phosphorus-poor soil conditions appear to be essential, because the plant species that typically occur in these grasslands are able to handle nutrient limitation, but not light limitation.

Improving our understanding of ecosystem responses to land-use intensification requires explicit consideration of linkages between aboveground and belowground communities. Here, we explore linkages between plant, soil microbial and nematode community compositions along a historical land-use intensity (hLUI) gradient. We used co-inertia analysis to investigate linkages between each paired community composition in 33 grasslands with similar hydrology and soil texture but contrasting hLUI and associated soil chemical properties (e.g. pH, phosphorus). We estimated the percentage cover of plant species, identified nematodes to genus level, and analysed the microbial community using phospholipid fatty acid (PLFA) profiling. Plant and nematode communities were more strongly linked as compared to either community’s links with microbes, although all pairwise comparisons were significant. Linkage strength did not depend on the degree of hLUI. We found significant variations in plant and nematode, but not in microbial, community compositions along the hLUI gradient. Large changes in soil fertility associated with hLUI have led to shifts in vegetation community composition matched by changes in the composition of different soil communities, or vice versa. The nematode community seems to be more responsive to vegetation composition than other trophic groups. Additional research in an experimental setting will elucidate the mechanisms underpinning the observed relationships.

Three experiments were conducted to find out the feeding type and age structure of nematodes in different soil habitats; to know the efficiency of different extraction techniques of nematodes and to observe the hatching behavior of Meloidogyne juvenile in a Baermann device. Bacterivore, Omnivore, Predator, Fungivore and Plant Parasitic nematodes were recorded in the soil of flower, vegetable, moss, grass, and corn and compost habitats. Bacterivore was the highest feeder (67.5%) in the soil habitats. In comparison of nematode extraction methods, Seinhorst method extracted more cysts (188), but less juvenile (34) and eggs (18) from cysts than stirring (145, 87 and 50, respectively) while AZC was found superior (936) over Cobb method (204) in extracting nematodes. The AZC method also extracted huge juvenile number from roots which was higher than Baermann funnel method. In Baermann funnel, juvenile hatched more in favorable condition than unfavorable condition which led to an increasing and decreasing pattern of hatching.

Summary Although biotic legacies of past agricultural practices are widespread and increasing in contemporary ecosystems, our understanding of the mechanisms driving such legacies is still poor. Forest understories on former agricultural land show low frequencies and abundance of typical woodland species when compared with ancient forests. These community shifts have been ascribed to the effects of dispersal limitation. A rarely considered mechanism is that post-dispersal processes driven by plant-associated communities determine the poor performance and recruitment of woodland indicators. Given the strong alterations in soil conditions due to former agricultural practices, we hypothesized that (abiotic) plant–soil feedbacks could be a major factor in community shifts. We addressed this hypothesis by comparing plant-associated communities in the soil and above the ground in ancient and post-agricultural alluvial forests; then, we experimentally tested whether the changes in biotic and abiotic soil properties could affect above-ground herbivore abundance and pressure and plant performance. Ancient and post-agricultural communities clearly differed in composition at different levels of the food web. Besides the plant community, we also observed the differences in the microbial and nematode community with increased abundance of root-feeding nematodes in post-agricultural soils. The composition of the above-ground invertebrate community did not differ in ancient and post-agricultural forest parcels; however, plants growing in post-agricultural sites showed higher abundance of invertebrate herbivores and suffered more herbivory. Nutrient analyses of soil and plants showed that increased levels of phosphorus (and to a lesser extent, nitrogen) made plants more nutritious for insect herbivores. Laboratory experiments further pointed to this mechanism as an explanation of the poorer performance of woodland indicators in post-agricultural woodlands. Our results point to biotic and abiotic plant–soil feedbacks coupled with herbivory as a new mechanism to explain the legacy effects in temperate forests. The modification of the below-ground community and soil abiotic characteristics by previous agricultural activity affects not only the plant growth but also the plant nutrient content in the compared understorey species, making them more susceptible to above-ground herbivory. Our results provide one of the first examples of integrating plant–soil feedback and above- and below-ground interactions to explain land-use legacies.

The pine wood nematode (PWN), Bursaphelenchus xylophilus, causes pine wilt disease and is transmitted by Monochamus beetles. An efficient trapping system for these organisms is essential for their early detection in threatened regions. A wet catching method, using monoethylene glycol (MEG) in a collecting cup to preserve captured insects, was suitable for catching longhorn beetles. As a second step in developing this technique, we studied the influence of MEG on nematode detection. When M. galloprovincialis carrying PWN were submerged in MEG, nematodes died within 24 h. The preservative altered certain morphological features of nematodes immersed in solutions of 10, 30 or 60% MEG, impeding their morphological identification. However, molecular identification was possible as long as the MEG concentration was below 70%. At higher concentrations, a rinsing step with water before DNA extraction was enough to allow molecular detection. Wet trapping requires less frequent monitoring than dry trapping, thus reducing maintenance and related costs., SCOPUS: ar.j, info:eu-repo/semantics/published

The root-knot nematodes (RKN), Meloidogyne spp., represent an important threat to yam (Dioscorea spp.) production in West Africa. With the aim to establish the diversity of RKN species affecting yam tubers, for control and resistance screening purposes, surveys were conducted in the main yam producing areas of Nigeria. Galled tubers (N = 48) were collected from farmers’ stores and markets in nine states in Nigeria and in one district in Ghana. RKN isolated from yam tubers were identified using enzyme phenotyping (esterase and malate dehydrogenase) and mitochondrial DNA (mtDNA) NADH dehydrogenase subunit 5 (Nad5) barcoding. Examination of 48 populations revealed that yam tubers were infested by Meloidogyne incognita (69%), followed by M. javanica (13%), M. enterolobii (2%), and M. arenaria (2%). Most of the tubers sampled (86%) were infected by a single species, and multiple species of RKN were detected in 14% of the samples. Results of both identification methods revealed the same species, confirming their accuracy for the identification of these tropical RKN species. In addition to M. incognita, M. javanica, and M. enterolobii, we report for the first time M. arenaria infecting yam tubers in Nigeria. This finding extends the list of yam pests and calls for caution when developing practices for yam pest management.

Damage caused to entomopathogenic nematodes by spray application is generally assessed by observing the viability of the infective juveniles under the microscope. To improve the quality and speed of this observation we developed an image processing technique and tested the efficacy of acetic acid and sodium chloride as chemical stimulants. Because of the lower standard error on the results obtained (0.7 vs 1.7), sodium chloride was eventually selected for all subsequent observations. The viability as observed with the image processing technique rose significantly with the time after the nematodes were suspended in water; however, viability as observed under the microscope was not influenced by the time. These differences can be attributed to the difference in type of stimulant (mechanical vs chemical) used. After nematodes had been in suspension for 3.5 h, the viability as measured using the image processing system was still significantly lower than the viability as measured under the microscope. This difference did not disappear after 24 h at 4, 15 or 24°C. Maintaining nematodes for 24 h at 35°C significantly decreased the viability to 5.9% (microscope) or 11.0% (image processing technique). The decrease in viability as observed with the image processing system corresponded better with the decrease in infectivity (i.e., 13.8%). Our results support further use of the image processing technique, not only to observe the viability of entomopathogenic nematodes but also to count the mobile or total number of nematodes of any species.

The food specificity of nematodes, their high number of species and high abundance in every habitat where decomposition takes place, indicate that the structure of the nematode assemblage has a high information content. Since nematodes respond quickly to changes in soil management and since the nematode fauna can be efficiently analysed, the structure of the nematode assemblage offers an interesting instrument to assess changes in soil conditions. We studied the effect of five organic amendments on the short-term nematode population dynamics and compared them to minerally fertilised and unfertilised plots. The experiment was started in 2005, and samples were taken in spring and autumn 2006 and spring 2007. In spring 2006, no clear differences among treatments in the diversity of free-living nematodes were observed, probably since the organic amendments were applied only twice, of which the last application was carried out 7 months before the sampling. At the second and third sampling, the enrichment index in the organically amended plots was higher than in the unamended plots, owing to the organic matter application. However, in plots amended with farmyard manure and cattle slurry the number of bacterivores increased significantly, while in the compost plots the fungivorous nematodes tended to be higher. This resulted in a low channel index for the manure and slurry plots, indicating a predominant bacterial decomposition pathway, and a higher channel index in the compost plots, suggesting a greater proportion of fungal decomposition. These assumptions on the decomposition of the applied organic matter were strongly supported by the composition of the soil microbial community, determined through PLFA analysis: in the compost plots the bacteria to fungi ratio was lower than in the manure and slurry plots. At all sampling occasions there was a remarkably lower abundance of plant-parasitic nematodes in plots amended with slurry and manure, indicating a negative impact of both amendments on plant-parasitic nematodes. We can conclude from this study that the fertiliser regimes affected the nematode assemblage, but that more samplings in the future are certainly necessary to assess adequately the impact of the different organic amendments.

Heterodera is a genus of cyst-forming nematodes, including the cereal cysts which can provoke yield reductions in grain crops. As little is known about the occurrence of these cysts in Belgian grain fields, a survey was organized, starting in Flanders. Soil samples were taken from 50 fields where cereals are grown in rotation with mainly beet, potato and vegetables. Cysts were extracted from the 112 samples and 10 individuals per sample were identified up to species level by morphometrical and morphological observations. The beet cyst nematode, Heterodera schachtii, was found in 34 fields (56%) at infestation levels varying from 0.6 to 1322 cysts/kg soil. Other Heterodera species (e.g. H. trifolii, H. mani) were found in low numbers and sometimes in mixtures with H. schachtii, but no cereal cysts were detected. This survey confirms that beet cyst nematodes are a problem in Flanders. The few cereal cysts that might be present were perhaps not detected due to the few individuals that were identified. For this reason, molecular identification tools which allow fast and accurate identification of Heterodera species would be very useful. It could be interesting to find out why cereal cysts are suppressed in our regions and to expand the survey to the Walloon region where more cereals are grown.

The effect of several passages through a centrifugal pump on the viability and activity of Steinernema corpocapsoe was investigated. A tendency of reduced viability was detected after 10 passages through the centrifugal pump, but the difference was not statistically significant. Activity decreased significantly from 91.9% to 83.6%. The experimental set-up was chosen to eliminate temperature increase. Therefore, the results prove that mechanical pump damage cannot be excluded as the cause of EPN damage during spray application.

Regional variability of European earthworm communities under different farming systems This work was funded by the European Commission Horizon 2020 project SoildiverAgro [grant agreement 817819].