Four studies were conducted to investigate plant-parasitic nematodes (PPN) of corn and soybean in ND. The first study investigated the incidence and abundance of vermiform PPN in ND corn fields in 2015 and 2016. Samples were collected from 300 corn fields across 20 counties. Seventy-two percent of the fields were positive for PPN. The major genera of PPN identified were Helicotylenchus, Tylenchorhynchus, Paratylenchus, Pratylenchus, Heterodera, Xiphinema, Hoplolaimus, and Paratrichodorus. The second study characterized SCN (SCN; Heterodera glycines) virulence phenotypes in ND. A total of 419 soybean fields across 22 counties were sampled during 2015, 2016, and 2017. Among these samples, 73 SCN field populations were successfully virulence phenotyped using the HG type tests. The HG types that were detected and confirmed in ND were HG type 0, 7, 2.5.7, 5.7, 1.2.5.7, and 2.7. The third study developed a new molecular method for detecting and identifying a new Pratylenchus sp. discovered in a soybean field in ND. A species-specific primer set, that can be used in both conventional and real-time polymerase chain reaction (PCR) assays, was designed from the internal transcribed spacer (ITS) region of ribosomal DNA. Laboratory experiments confirmed that the primers only amplified DNA of the target nematode species but not the non-target species used in the specificity tests. Practically, DNA from as little as a single nematode could be used to specifically identify the new Pratylenchus sp. using the molecular diagnostic methods developed in this study. The fourth study was conducted to ascertain resistance levels of 20 soybean cultivars to the new Pratylenchus sp. Combined results of four trials indicated that seven of the cultivars were moderately resistant, ten were moderately susceptible, four were susceptible, and none of the cultivars tested were resistant. Analysis of the habitat preference of the new Pratylenchus sp., revealed that above or close to 50% of the nematode population resided in roots at nine weeks after planting for a majority of the cultivars evaluated. Results from these studies will be helpful in improving nematode detection and developing management strategies to control plant-parasitic nematodes in ND corn and soybean fields.

No description available.

No description available.

The Wonderfontein Cave is located within the Witwatersrand Basin (Gauteng province, South Africa) and is associated with the river banks of the Wonderfontein Spruit. This cave system has for many years been subjected to the influx of polluted mine water. Since subterranean environments remain poorly studied, it is unknown what the effect of this might be on the associated ecosystem. Furthermore, water that enters the Wonderfontein Cave poses a severe health threat as it drains into the underlying aquifer, which is abstracted for human and animal use. The general aim of this study was to determine the extent of metal pollution (enrichment), as well as to study the toxicity hazard potential of the soils and sediments associated with the Wonderfontein Cave. The objectives of this study were to (1) quantify the extent of anthropogenic metal pollution of water, soils and sediments associated with the Wonderfontein Cave (2) and assessing the toxicity hazard potential of these substrates; (3) determining whether nematode taxa and C. gariepinus individuals represent isolated communities and a population within the Wonderfontein Cave, respectively; (4) measuring the effect of mining-associated pollutants on the soil and sediment health of the Wonderfontein Cave by making use of nematodes to serve as bioindicators; (5) evaluating and comparing biomarker responses to metal bioaccumulation in C. gariepinus populations associated with the Wonderfontein Cave and epigean (surface) environments and lastly (6) comparing the results of the above identified assessments over both a temporal and spatial scale. Sampling was undertaken during April (1st sampling interval) and September (2nd sampling interval) 2013, which respectively represented the end of the high and low flow periods. Also, sampling of the subterranean (Wonderfontein Cave) and associated surface (Wonderfontein Spruit) environments were undertaken. The findings of this study suggested that especially the sediments associated with the Wonderfontein Cave have been subjected to severe nickel, copper, zinc, cobalt, aluminium, cadmium, lead and uranium enrichment. Also, the concentrations of many of the studied metals exceeded the respective water, soil and sediment environmental quality guidelines. Thus, also taking into consideration that most of the sediments were classified as being toxic, a severe threat is posed to the health of the associated biota. Although 60 nematode genera were identified from soil and sediments samples collected from the respective sampling sites associated with the Wonderfontein Cave and Spruit, it was concluded that most of these genera were likely only temporary residents of the subterranean environment. Even though plant-parasitic and nonparasitic nematodes were present, most of the collected soil and sediment samples were dominated by bacterivores (non-parasitic nematodes). Zero genetic divergence was recorded between the C. gariepinus populations associated with the Wonderfontein Cave and Stoffels Dam (Wonderfontein Spruit). However, significant temporal and spatial variation was observed in some bioaccumulated metals and biomarker responses within and between the respective C. gariepinus populations. Furthermore, the metal bioaccumulation levels present in both these fish populations pose a substantial threat to human health and are thus not fit for consumption. Also, no significant fish condition differences were observed between the C. gariepinus populations associated with the Wonderfontein Cave and Spruit. This study served as an initiative to create awareness and promote the conservation of Africa’s karst landscapes. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

The Wonderfontein Cave is located within the Witwatersrand Basin (Gauteng province, South Africa) and is associated with the river banks of the Wonderfontein Spruit. This cave system has for many years been subjected to the influx of polluted mine water. Since subterranean environments remain poorly studied, it is unknown what the effect of this might be on the associated ecosystem. Furthermore, water that enters the Wonderfontein Cave poses a severe health threat as it drains into the underlying aquifer, which is abstracted for human and animal use. The general aim of this study was to determine the extent of metal pollution (enrichment), as well as to study the toxicity hazard potential of the soils and sediments associated with the Wonderfontein Cave. The objectives of this study were to (1) quantify the extent of anthropogenic metal pollution of water, soils and sediments associated with the Wonderfontein Cave (2) and assessing the toxicity hazard potential of these substrates; (3) determining whether nematode taxa and C. gariepinus individuals represent isolated communities and a population within the Wonderfontein Cave, respectively; (4) measuring the effect of mining-associated pollutants on the soil and sediment health of the Wonderfontein Cave by making use of nematodes to serve as bioindicators; (5) evaluating and comparing biomarker responses to metal bioaccumulation in C. gariepinus populations associated with the Wonderfontein Cave and epigean (surface) environments and lastly (6) comparing the results of the above identified assessments over both a temporal and spatial scale. Sampling was undertaken during April (1st sampling interval) and September (2nd sampling interval) 2013, which respectively represented the end of the high and low flow periods. Also, sampling of the subterranean (Wonderfontein Cave) and associated surface (Wonderfontein Spruit) environments were undertaken. The findings of this study suggested that especially the sediments associated with the Wonderfontein Cave have been subjected to severe nickel, copper, zinc, cobalt, aluminium, cadmium, lead and uranium enrichment. Also, the concentrations of many of the studied metals exceeded the respective water, soil and sediment environmental quality guidelines. Thus, also taking into consideration that most of the sediments were classified as being toxic, a severe threat is posed to the health of the associated biota. Although 60 nematode genera were identified from soil and sediments samples collected from the respective sampling sites associated with the Wonderfontein Cave and Spruit, it was concluded that most of these genera were likely only temporary residents of the subterranean environment. Even though plant-parasitic and nonparasitic nematodes were present, most of the collected soil and sediment samples were dominated by bacterivores (non-parasitic nematodes). Zero genetic divergence was recorded between the C. gariepinus populations associated with the Wonderfontein Cave and Stoffels Dam (Wonderfontein Spruit). However, significant temporal and spatial variation was observed in some bioaccumulated metals and biomarker responses within and between the respective C. gariepinus populations. Furthermore, the metal bioaccumulation levels present in both these fish populations pose a substantial threat to human health and are thus not fit for consumption. Also, no significant fish condition differences were observed between the C. gariepinus populations associated with the Wonderfontein Cave and Spruit. This study served as an initiative to create awareness and promote the conservation of Africa’s karst landscapes. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Pratylenchus brachyurus é um dos nematóides mais disseminados na cultura do algodão nas áreas produtoras do Brasil. Sua patogenicidade ao algodoeiro, entretanto, é pouco estudada. Os objetivos deste trabalho foram: i) correlacionar níveis populacionais iniciais crescentes de P. brachyurus (0, 12.000, 30.000 e 75.000 exemplares/ planta) com os danos causados ao algodoeiro \'Delta Opal\'; ii) avaliar a patogenicidade de populações de P. brachyurus em algodoeiros \'Delta Opal\' e \'Fibermax 966\'; iii) testar cultivares de algodão em relação à reprodução de três populações de P. brachyurus ; iv) caracterizar a relação parasito-hospedeiro (em termos de suscetibilidade/resistência) de alguns adubos verdes, coberturas vegetais e pastagens a Pratylenchus brachyurus; v) caracterizar molecularmente populações de P. brachyurus, através de PCR-RFLP e seqüenciamento da região ITS-1 do rDNA. Os resultados sugerem que P. brachyurus é patógeno pouco agressivo da cultura do algodão, já que não se verificaram danos significativos às plantas em densidades populacionais do nematóide inferiores a 12.000 exemplares/ planta. Em relação às cultivares, todas foram suscetíveis a P. brachyurus . Entre as espécies vegetais testadas, as que se mostraram resistentes a P. brachyurus foram Crotalaria spectabilis, C. breviflora, amaranto \'BRS Alegria\', nabo forrageiro \'Comum\' e as cultivares de aveia preta Campeira Mor, IPFA 99006, Comum, CPAO 0010 e Garoa. As análises de PCRRFLP revelaram variabilidade genética entre as diferentes populações de P. brachyurus estudadas, em função dos diferentes padrões de bandas encontrados para as populações estudadas. O seqüenciamento da região ITS-1 do rDNA confirmou a variabilidade observada pela digestão enzimática, além de evidenciar heterogeneidade das regiões 18S e ITS-1 do rDNA de P. brachyurus / Although Pratylenchus brachyurus is widespread in Brazilian cotton fields, information about its importance as a cotton pathogen is scarce. The objectives of this work were: i) correlate crescent initial population densities (0; 12,000; 30,000; and 75,000 nematodes/ plant) with damage on cotton \'Delta Opal\'; ii) measure the pathogenic effect of P. brachyurus on cotton \'Delta Opal\' and \'Fibermax 966\'; iii) characterize the reaction of cotton cultivars to three populations of P. brachyurus ; iv) characterize the host reaction (in terms of susceptibility/ resistance) of some green manures, cover crops and pastures to two populations of P. brachyurus; v) characterize different populations of P. brachyurus by PCR-RFLP and sequencing of ITS-1 rDNA region. Results suggest that P. brachyurus is an eventual pathogen of cotton, since high population levels were necessary to reduce plant growth (< 12,000 nematodes/ plant). All cotton cultivars tested were rated as susceptible to P. brachyurus In relation to crop species tested, Crotalaria spectabilis, C. breviflora, amaranth \'BRS Alegria\', oil radish \'Comum\', and the black oat cultivars Campeira Mor, IPFA 99006, Comum, CPAO 0010, and Garoa were resistant to P. brachyurus PCR-RFLP showed intraspecific variability for different population of P. brachyurus studied. Sequencing of the ITS-1 rDNA region confirmed the results of the enzymatic digestion and demonstrated heterogeneity of 18S and ITS-1 rDNA regions of P. brachyurus.

Les nématodes phytoparasites (NPP) sont des vers ronds microscopiques que l’on retrouve en communautés dans les sols agricoles. Les NPP les plus communs n’occasionnent pas de dégâts sur les cultures. Cependant M. chitwoodi, un NPP règlementé à l’échelle européenne, peut engendrer d’importantes baisses de rendement. Pour caractériser le risque de son implantation, nous nous sommes intéressés aux communautés indigènes en France afin d’identifier celles capables de le limiter suite à une introduction. Nous avons, dans un premier temps, décrit les communautés de NPP à l'échelle d'un paysage agricole, puis à l'échelle de neuf régions françaises. Ces investigations ont montré des communautés peu différenciées en termes de richesse spécifique mais variables en termes d’abondance. Si les variables environnementales expliquent le mieux la structure de ces communautés de NPP à une large échelle géographique, certaines pratiques culturales(labour, application de produits phytosanitaires) influencent fortement les communautés à l’échelle locale. Dans un second volet, nous avons étudié le potentiel de différentes communautés à limiter le développement de M. chitwoodi notamment par la compétition. Il semble que les communautés possédant les plus hauts niveaux d’abondance globale, indépendamment des taxa présents, permettent de diminuer la multiplication de M. chitwoodi. Cette thèse apporte donc des éléments de compréhension sur le fonctionnement des communautés de NPP dans les agrosystèmes français et leur potentiel à limiter le l’établissement de M. chitwoodi pour pouvoir prédire le r / Plant-parasitic nematodes (PPN) are microscopic worms that occur in communities in almost every agricultural soils. Commonly found PPN are usually harmless for the plants. However, M. chitwoodi, a PPN highly regulated in EU can induce important yield losses. In order to improve risk assessment of M. chitwoodi implantation, we studied French native PPN communities to identify those that can limit its establishment shortly after an introduction. We firstly described PPN communities in various agrosystems, at a landscape scale and then in nine French regions. Despite the quite homogeneous species richness observed across the fields sampled, we highlighted strong PPN taxa abundance variations. Environmental variables seemed to mainly drive the PPN communities structure at a large geographic scale but cultural practices(tillage and pesticides uses) seemed to explain the communities variation at the local scale. Secondly, we studied the capacity of different PPN communities to limit M. chitwoodi development through competition. It appeared that PPN communities with high global abundance, regardless of the taxa present, are able to decrease M. chitwoodi multiplication. The results of this PhD thesis bring some elements about the structure and functioning of PPN communities in French fields and their ability to reduce the M. chitwoodi establishment in order to predict its implantation risk.

Pratylenchus brachyurus é um dos nematóides mais disseminados na cultura do algodão nas áreas produtoras do Brasil. Sua patogenicidade ao algodoeiro, entretanto, é pouco estudada. Os objetivos deste trabalho foram: i) correlacionar níveis populacionais iniciais crescentes de P. brachyurus (0, 12.000, 30.000 e 75.000 exemplares/ planta) com os danos causados ao algodoeiro \'Delta Opal\'; ii) avaliar a patogenicidade de populações de P. brachyurus em algodoeiros \'Delta Opal\' e \'Fibermax 966\'; iii) testar cultivares de algodão em relação à reprodução de três populações de P. brachyurus ; iv) caracterizar a relação parasito-hospedeiro (em termos de suscetibilidade/resistência) de alguns adubos verdes, coberturas vegetais e pastagens a Pratylenchus brachyurus; v) caracterizar molecularmente populações de P. brachyurus, através de PCR-RFLP e seqüenciamento da região ITS-1 do rDNA. Os resultados sugerem que P. brachyurus é patógeno pouco agressivo da cultura do algodão, já que não se verificaram danos significativos às plantas em densidades populacionais do nematóide inferiores a 12.000 exemplares/ planta. Em relação às cultivares, todas foram suscetíveis a P. brachyurus . Entre as espécies vegetais testadas, as que se mostraram resistentes a P. brachyurus foram Crotalaria spectabilis, C. breviflora, amaranto \'BRS Alegria\', nabo forrageiro \'Comum\' e as cultivares de aveia preta Campeira Mor, IPFA 99006, Comum, CPAO 0010 e Garoa. As análises de PCRRFLP revelaram variabilidade genética entre as diferentes populações de P. brachyurus estudadas, em função dos diferentes padrões de bandas encontrados para as populações estudadas. O seqüenciamento da região ITS-1 do rDNA confirmou a variabilidade observada pela digestão enzimática, além de evidenciar heterogeneidade das regiões 18S e ITS-1 do rDNA de P. brachyurus / Although Pratylenchus brachyurus is widespread in Brazilian cotton fields, information about its importance as a cotton pathogen is scarce. The objectives of this work were: i) correlate crescent initial population densities (0; 12,000; 30,000; and 75,000 nematodes/ plant) with damage on cotton \'Delta Opal\'; ii) measure the pathogenic effect of P. brachyurus on cotton \'Delta Opal\' and \'Fibermax 966\'; iii) characterize the reaction of cotton cultivars to three populations of P. brachyurus ; iv) characterize the host reaction (in terms of susceptibility/ resistance) of some green manures, cover crops and pastures to two populations of P. brachyurus; v) characterize different populations of P. brachyurus by PCR-RFLP and sequencing of ITS-1 rDNA region. Results suggest that P. brachyurus is an eventual pathogen of cotton, since high population levels were necessary to reduce plant growth (< 12,000 nematodes/ plant). All cotton cultivars tested were rated as susceptible to P. brachyurus In relation to crop species tested, Crotalaria spectabilis, C. breviflora, amaranth \'BRS Alegria\', oil radish \'Comum\', and the black oat cultivars Campeira Mor, IPFA 99006, Comum, CPAO 0010, and Garoa were resistant to P. brachyurus PCR-RFLP showed intraspecific variability for different population of P. brachyurus studied. Sequencing of the ITS-1 rDNA region confirmed the results of the enzymatic digestion and demonstrated heterogeneity of 18S and ITS-1 rDNA regions of P. brachyurus.

Na região dos cerrados, as principais culturas de cobertura utilizadas para a produção de palha no sistema de plantio direto são o milheto (Pennisetum glaucum R. BR.) e as aveias (Avenas spp.). No entanto, a resposta dessas espécies vegetais frente ao nematóide das lesões (Pratylenchus brachyurus) e o das galhas (Meloidogyne incognita) são escassas. O objetivo do presente trabalho é de verificar a resposta de genótipos de milhetos, aveias e outras coberturas vegetais a Pratylenchus brachyurus e de aveias a Meloidogyne incognita sob condições controladas. Desenvolveram-se quatro experimentos no total, no experimento 1, os cultivares de milhetos testados foram resistentes ao nematóide (FR<1,0) com exceção da cultivar ADR 500 (população BA). No experimento 2, as aveias pretas contribuíram para a redução populacional (resistentes) de P. brachyurus, fato oposto, pode ser verificado para as aveias branca e amarela (suscetíveis). No terceiro experimento, diferentemente do verificado no experimento 1, os milhetos se mostraram suscetíveis a P. brachyurus, e, o sorgo BRS-800 foi a cobertura que mais incrementou a densidade do nematóide, equiparando-se estatisticamente com a soja BRS 133. No quarto experimento, verificou-se aumento da densidade das três populações de M. incognita nas aveias pretas testadas, em contraposição à redução verificada na aveia branca UFRGS 17 e amarela São Carlos. / In Cerrado region, the main cover crop used in no tillage system are the pearl millet (Pennisetum glaucum) and the oats (Avena spp.). However, the response of these vegetable species to lesion nematode (Pratylenchus brachyurus) and to root-knot nematode (Meloidogyne incognita) is scarce. The aim of the present work was verify the response of the pearl millet genotypes, oats and other cover crops to P. brachyurus and of oats to M. incognita under greenhouse conditions. Four experiments were done; in experiment 1, the pearl millet cultivars tested were resistant to nematode (FR<1.0) with exception of the cultivar ADR 500 (population BA). In experiment 2, the black oats reduced the P. brachyurus population (resistant); contrarily, white and yellow oats were susceptible. In third experiment, the pearl millets showed as susceptible to P. brachyurus, and the sorghum BRS-800 was the cover crop more susceptible to nematode, statistically closed to soybean BRS 133. In experiment 4, black oats increased the three populations of M. incognita tested, instead the reduction verified in white oat UFRGS 17 and yellow São Carlos.

Diese Arbeit untersucht die Reaktion der Stieleiche auf pflanzenparasitären Nematoden mittels RNA-Sequenzierung und Analyse von stabilen Isotopen und Fettsäuren. Einblicke in Rhizosphäreninteraktionen wurden über mutualistische Partner (Ektomykorrhizapilze, Rhizosphärenhelferbakterien), fungivore Collembolen und multitrophische Gemeinschaften gewonnen. Die Struktur und Biomasse der Mikroorganismen sowie die Fitness der Eichen wurden erfasst. Die Effekte wurzelfressender Nematoden auf die Eiche wurden durch das endogene rhythmische Wachstum des Baumes reguliert. Die Nematoden lösten eine stärkere Reaktion während des Sprosswachstumsschubs aus, u.a. Aktivierung von Abwehrmechanismen und Hemmung der Photosynthese, wohingegen beim Wurzelwachstumsschub pathogen bezogene Signale unterdrückt waren. Die Anwesenheit des Pilzsymbionten schwächte die Pflanzenabwehr und verbesserte die Stresstoleranz, was indirekt das Wachstum der Mikroorganismen förderte. Die Helferbakterien begünstigten den Mykorrhizapilz, was wiederum das Pflanzenwachstum stimulierte und dem negativen Effekt der Nematoden entgegenwirkte. Parasitäre Nematoden und fungivore Collembolen beeinflussten die Verteilung des pflanzlichen Kohlenstoffes unabhängig voneinander; Nematoden verringerten und Collembolen verbesserten die Allokation von Photoassimilaten in Gram-postiven Bakterien. Zudem war steigende trophische Diversität der Bodenfauna in der Rhizosphäre entscheidend für die Balance innerhalb der mikrobiellen Gemeinschaft, welche das Pflanzenwachstum fördert. Diese Arbeit stellt die Bedeutung der endogenen Ressourcenzuteilung von Pflanzen für unterirdische biotische Wechselbeziehungen heraus. Diese Pflanzenstrategie als bedeutender Faktor für Rhizosphärenprozesse sollte in zukünftige Studien Berücksichtigung finden. Die Einbeziehung der Hauptakteure in der Rhizosphäre ermöglicht zudem ein realistischeres Bild von Nematoden-Pflanzen Interaktionen und damit ein effektiveres Management. / This thesis investigated the response of Pedunculate oak to the plant-parasitic nematode Pratylenchus penetrans, using RNA-sequencing, stable isotope labelling and fatty acid analyses. Insight into rhizosphere interactions was gained by employing beneficial biotic partners (ectomycorrhizal fungi, rhizosphere helper bacteria), fungal grazers (Collembola) and multitrophic environments. Microbial biomass and community structure as well as oak fitness were assessed. The effects of root-feeding nematodes on oak were largely governed by the endogenous rhythmic growth of the tree. The nematodes triggered a stronger response during shoot flush, e.g. activation of multi-layered defence mechanisms and repression of photosynthesis, as compared to root flush where pathogen-related signalling was repressed. With the presence of the mycorrhizal symbiont plant defence was attenuated and stress tolerance enhanced, indirectly promoting the growth of rhizosphere microorganisms. The helper bacteria fostered the ectomycorrhizal fungus, which in turn stimulated plant growth, counteracting the negative effects of nematodes. Plant-parasitic nematodes and Collembola grazers had independent roles in plant carbon allocation patterns, with nematodes hampering whilst Collembola enhancing the flux of recent photoassimilates to Gram-positive bacteria. Lastly, increasing trophic diversity of the soil fauna in the rhizosphere of oaks was crucial for the maintenances of a microbial community equilibrium that promotes plant growth. In sum, this study highlights the importance of endogenous resource allocation pattern of plants in determining the outcome of belowground biotic interactions. Therefore such plant traits should be considered as important drivers for rhizosphere processes in future studies. Moreover, taking into account the rhizosphere main players in studies on parasitic nematode-plant interactions will result in a more realistic picture and thus more effective nematode management.