No description available.

No description available.

No description available.

The plant parasitic cyst nematode Heterodera schachtii forms a specialised feeding cell in the roots of host plants. The feeding site, termed a syncytium, is the sole source of nutrition for the developing parasitic nematode. The initiation and development of a syncytium requires extensive re-programming of gene expression in the specific root cells selected by the nematode for feeding site initiation. Auxin is postulated to playa role in this re-differentiation process. Activation of the auxin-responsive promoter DR5 in syncytia indicates an increase in perceived auxin levels. To determine whether or not the increase in auxin is required for the formation of syncytia, auxin signalling mutants were infected with H. schachrii for analysis of syncytial and nematode development. Measuring the size of syncytia throughout H schachtii development revealed sign ificantly smaller syncytia were formed in the auxin signalling mutant, axrl-12 in comparison to wild type plants. To elucidate biological processes mediated by auxin during syncytial development in silico analysis was performed on syncytia transcriptome data; this was used to identify genes upregulated in the syncytia that contain auxin-responsive elements in the promoter region. The cytoplasmic contents of syncytia formed in axrl -12 and wild type plants were microaspirated; this material was used for qRT-PCR analysis of auxin responsive gene expression. qRT-PCR analysis revealed that genes encoding cell wall remodelling enzymes were differentially expressed in syncytia fonned on axr 1-12 plants. The effects of altered cell wall remodelling enzyme expression on the structure of syncytia were investigated by obtaining transverse sections through syncytia fanned in wild type and axr 1-12 plants. Monoclonal antibodies to defined glycans and a cellulose binding module were used to localise carbohydrate and structural protein components in the cell walls of syncytia. The carbohydrate components of syncytia were found to be similar but differences were observed in the expression of structural proteins in syncytia formed in axr1-J2 and wild type plants. Additionally, cell wall degradation had occurred more extensively in syncytia formed in wild type plants in comparison to syncytia in axrJ·12. Cell proliferation in axrJ-12 and wild type roots during syncytial development was examined and found to be reduced in the auxin signalling mutant, indicating a role for auxin mediating cell-cyc\e activation during the development of syncytia. This study provides the first insight into the biological processes mediated by auxin during the development of syncytia by H schachtii in Arabidopsis thaliana .

A permanent pasture site at Spen Farm, Tadcaster (Field number 469 / 462), was selected under Lolium perenne, where a high population of Longidorus spp occurs. Longidorus elongatus were separated from the other two Longidorus spp. present by its morphometric characteristics. L elongatus has an annual life cycle, with the first stage juvenile being relatively abundant from May to July with a peak in June.

No description available.

Despite current control measures, plant parasitic nematodes are estimated to be responsible for > $100 billion of damage to worldwide crop production per annum. Current nematicides are highly toxic, and due to health and environmental safety concerns, many are being withdrawn from the market under directive 914/414/EEC. Alternative control strategies are urgently required. The cysteine proteinases papain, actinidain and recombinant endoproteinase B isoform 2 (R.EP-B2) have been demonstrated to affect the mobility of M. incognita J2s; 50.7 μM R.EP-B2, 101.7 μM papain and 200.3 μM actinidain immobilised 50% of the M. incognita population. Papain has also been demonstrated to affect the infection of plants by M. incognita, 5 μM papain reduced the attraction to and invasion of A. thaliana by 41.2 + 25.6% and 80.4 + 10.5% respectively. M. incognita J2s showed extensive damage to and removal of the cuticle when treated with 100 μM papain. MALDI-TOF analysis identified a number of M. incognita proteins affected by the papain treatment; of particular interest were a cuticle preprocollagen and a rhodopsin-like GPCR chemoreceptor. Proteins of these types are essential for movement and host location, disrupting their function helps to explain the loss of mobility and reduction in A. thaliana infection observed in the bioassays. Finally transgenic A. thaliana was generated with the barley cysteine proteinase endoproteinase B isoform two under the control of the root cap specific MDK4-20. The preliminary testing of these plants showed a reduction in root invasion similar to that obtained with papain.

Thesis(M.Sc.(Plant Protection))-- University of Limpopo,2019 / Previously, cucurbitacin-containing phytonematicides that were drench-applied in black plastic containers filled with pasteurised loam soil when placed on the soil surface had no effect on suppression of population densities of root-knot (Meloidogyne species) nematodes. The active ingredients of cucurbitacin-containing phytonematicides, namely, the cucurbitacins, had been shown to be thermophilic, with the failure of the products explained from the view of the variability induced by container-type and aboveground positioning. The view was investigated further using Nemarioc-AL and Nemafric-BL phytonematicides as influenced by container-type and positioning on growth of tomato (Solanum lycopersicum L.) plants and suppression of M. incognita population densities. Tomato cv. ′Floradade′ seedlings were transplanted into 30-cm-diameter brown pot belowground, brown pot aboveground, black pot belowground, black pot aboveground, 5 L polyethylene plastic bag belowground and 5 L polyethylene plastic bag aboveground, each containing 5-dm3 steam-pasteurised sandy loam soil amended with Hygromix at 3:1 (v/v) ratio. Seedlings were inoculated with 2000 eggs and second-stage juveniles (J2) of M. incognita race 2, with Nemarioc-AL and Nemafric-BL phytonematicides applied once 17 days after inoculation in both Experiment 1 and Experiment 2. Also, standard cultural practices were applied throughout the trial. At 56 days after inoculation, container-type and positioning had significant effects on various plant growth and essential nutrient element variables in Experiment 1 and Experiment 2, except that the six treatments did not have significant effects on nutrient elements and nematode population densities in Experiment 2. Relative to brown plastic pot belowground, treatments either increased or decreased plant growth, essential nutrient elements and nematode densities in Experiment 1, with selective similaritiesin Experiment 2. Specifically, nematode variables except for J2 in soil and total nematode population densities were significantly affected by the treatments in Experiment 2. Relative to the standard, plastic bag belowground increased J2 in soil and total population in soil by 18%. In conclusion, both container-type and positioning had effects on the efficacy of phytonematicides on plant growth, accumulation of essential nutrient elements and suppression of nematode population densities. Consequently, in trials where cucurbitacin-containing phytonematicides are conducted in microplots, brown plastic pots with the belowground positioning should be used to enhance the efficacy of the phytonematicides in stimulating plant growth and suppression of nematode population densities.

The Incomati River Estuary is prone to pollutants from anthropogenic activities such as agricultural and industrial activities in the upper catchments. The main aim of the study was to use free-living nematodes as pollution indicators in the Incomati River Estuary. The main objectives were to determine the relationship between nematodes assemblage and environmental variables, and to identify environmental factors that play a role in nematodes community structuring. Lastly, it was to identify free-living nematode genera that can be used as pollution indicators in the Incomati River Estuary. Four sites were selected following the salinity gradient of the Incomati River Estuary. Site E1 with a salinity range of 0-3NST (Oligohaline Zone), E2 with a salinity 3-5NST (Euhaline Zone), E3 with a salinity 6-18NST (Mesohaline Zone), and E4 with 20-27 NST (Polyhaline Zone) were selected and monitored bi-monthly from June 2017 to April 2018. Two sediments samples were collected per site during neap tide using a handheld perplex corer which was 1m long with a 3.6 diameter and 10cm penetration height. Plastic bottles with a height of 13cm and a diameter of 7cm were used to store the sediment samples. One of the two sediment samples was used for free-living nematodes, and the other bottle was used for the analysis of environmental factors. All environmental factors were analysed at Labserve Laboratory, Mbombela Town, Mpumalanga Province. Sediment particle size and organic matter analyses were done following the procedure set by Parker (1983) and Buchanan (1971) respectively. Metal analysis was done following the procedure used by Gyedu-Ababio et al.1999. Nutrients were done using different methods. For nitrates (NO3) analysis, a copper cadmium method by Bate and Heelas, 1975 was used, while a method designed by Strickland and Parson, 1972 was used to analyse orthophosphate. A mixed acid digestion procedure of Oles and Dean 1965 was followed for total phosphate. A method by Lorenzen and Jeffrey, 1980 was used for the analysis of chlorophyll-a. Heterotrophic bacteria analysis were done following a procedure by (Atlas, 1997). Nematodes were extracted using a method by Furstenberg et al.1978, with sucrose as a separating agent. Nematodes were counted following a procedure by Giere, 1993. Nematodes feeding types were investigated using Wieser, 1953 procedure. Different statistical packages including PRIMER version 6 were used to analyse the data. A Bray-Curtis Cluster analysis indicated a similarity between sites E1 (Oligohaline Zone) and E2 (Euhaline Zone), and between site E3 (Mesohaline Zone) and E4 (Polyhaline Zone) which was attributed to similar sediment particle sizes distribution within the sites. There was no significant difference (p>0.05) of sediments particle size between the sites. The highest concentration of metals was found at site E2 which was situated in the Euhaline Zone, whilst the second highest concentration was found at site E1 which was situated in the Oligohaline Zone. A PERMANOVA analysis indicated that there was a significant difference (p<0.05) of Metal concentration between sites sampled. The PCA analyses indicated that there was a positive correlation between Metals and Sediment Particle Size such as Granules. It was observed that sediment particle size and organic matter influenced the distribution of metals in the Estuary. The highest concentration of chlorophyll-a and nitrates (NO3) were found at site E3 which was situated in the Mesohaline Zone, and the second highest was found at site E4 which was situated in the Polyhaline Zone. There was a positive correlation between Heterotrophic bacteria and environmental factors such as zinc, fine sand, very fine sand and mud. This indicated that certain metals and sediment particles size played a role in structuring food source for meiofauna, especially nematodes. The number of free-living nematodes were found to decrease towards site E1. This indicated that salinity influenced the diversity and density of free-living nematodes in the estuary. Site E2 had the lowest diversity and richness followed by site E1. The lower diversity, richness and Maturity Index at site E2 and E1 indicated that these sites were under stress. A Bray-Curtis Cluster analysis indicated that there was a spatio-temporal variation of diversity and density of free-living nematodes in the estuary. All four nematodes feeding types were found in the Estuary and feeding type 1B was the dominant feeding type at the sites, followed by feeding type 2A. The highest number of feeding type 1B (non-selective deposit feeders) was identified at site E2. The life strategy characterisation (colonizer- persisters) indicated that site E2 was dominated by colonizer and intermediate genera (c-p 2 and 3), which indicated that the site was under stress. The study found that genera such as Terschellingia and Theristus were pollution indicators because they were found in higher abundance at a site that was mostly polluted by metals, organic matter, and total phosphate. Further studies in other River Estuaries in South Africa and SADC should be undertaken to add to the findings of the current study. / Environmental Studies / Ph. D. (Environmental Sciences)

Aux Antilles, dans les plantations de bananes en monoculture mécanisée, l'un des principaux problèmes à résoudre est le contrôle des populations de nématodes phytoparasites. Dans cette thèse, les effets d'apports de différentes matières organiques (MO), brutes ou compostées, sur la régulation biologique des nématodes ont été étudiés, cet effet suppresseur ayant déjà été montré sur d'autres cultures. L'analyse de la littérature sur le sujet montre que les effets d'un apport de MO sur les populations de nématodes phytoparasites et sur leurs dégâts sont complexes et varient fortement en fonction de la nature biochimique du produit et de l'espèce de nématode. Ainsi, les matières organiques qui libèrent beaucoup d'azote minéral en se décomposant favorisent la croissance des racines, ce qui peut augmenter la ressource alimentaire des nématodes phytoparasites et/ou la tolérance des plantes à leurs attaques. La décomposition des matières apportées peut libérer des composés nématotoxiques. Enfin, l'apport de carbone peut entrainer une diversification des communautés de nématodes, une complexification des réseaux trophiques et, par la suite, favoriser la régulation biologique des nématodes phytoparasites par les espèces appartenant aux niveaux trophiques supérieurs et par la microflore. Nous avons, par une étude fine de la structure des communautés de nématodes et le suivi de la croissance des jeunes plants de bananier, cherché à évaluer l'induction de la régulation biologique des nématodes parasites du bananier dans une sole bananière par un apport de MO, au moyen de deux expérimentations en pots conduites pendant 13 semaines. Les MO testées étaient quatre MO brutes et quatre MO compostées. L'expérience sur les MO brutes a montré que trois des quatre MO (bagasse, écumes de sucrerie et déchets verts) ont entrainé une diminution des populations de nématodes parasites dans les racines du bananier, l'intensité de cette régulation dépendant de l'espèce. En revanche, le quatrième type de MO, des boues de station d'épuration, n'a pas permis de diminuer la pression parasitaire. Les différences de croissance des systèmes racinaires n'ont pas été un facteur explicatif des régulations observées et les meilleures conditions de croissance observées n'ont pas réduit les impacts des nématodes phytoparasites sur les racines. Seules les écumes de sucrerie ont entrainé un impact positif global sur la plante, en diminuant la pression parasitaire tout en augmentant sa croissance. La bagasse et les déchets verts, principalement composés de lignines et de cellulose, ont entrainé une modification significative de la structure des communautés de nématodes, avec un fort accroissement des populations de nématodes fongivores et, avec la bagasse, de nématodes carnivores. L'expérience en pot sur les MO compostées a montré que les trois composts commerciaux produits par SITA VERDE (Biogwa, Ecogwa B, Ecogwa D) et l'amendement organique commercial Vegethumus (de Phallipou-Frayssinet) avaient engendré une diminution du parasitisme et que ce contrôle dépendait de l'espèce de nématodes phytoparasites. Dans cet essai, le contrôle des nématodes parasites du bananier est apparu lié à la biomasse racinaire totale des bananiers. L'apport des composts Ecogwa D et Vegethumus a augmenté la taille des populations de nématodes microbivores, mais seul Vegethumus a accru la voie de décomposition fongique. [...] Suite et fin du résumé dans la thèse. / In French West Indies, banana crops are generally managed as an intensive mechanized monoculture, and one of main problems to solve is the control of plant-parasitic nematodes. In this study, the effects of the input of different organic materials, gross or composted, on the biological control of nematodes were investigated. The analyze of the literature showed that the effects of an organic material input on plant-parasitic nematode populations and on their damage on the plant are complex and vary highly according to the biochemical characteristics of the products and the plant-parasitic nematode species. Thus, organic materials that release great amounts of mineral nitrogen during their decomposition promote root growth, which increases the feeding resource for plant-parasitic nematodes and/or plant tolerance to their attacks. Organic material decomposition can also release nematotoxic chemical compounds. Lastly, carbon input can lead to nematode community diversification, soil food web complexification, and, as a result, favoring the biological control of plant-parasitic nematodes by top predators or microflora. We evaluated the induction of the biological control of banana parasitic nematodes by an organic input, using soil nematofauna analyses and measuring the growth of young banana plants. We thus conducted two pot experimentations during 13 weeks. The organic materials tested were four raw and four composted organic materials that were locally available. The raw organic materials trial showed that three amongst the four amendments (sugarcane bagasse, sugarcane refinery sludge and plant residues) led to a decrease of parasitic nematode populations within banana roots, the control efficiency depending on nematode species. In contrast, the fourth type of organic material, sewage sludge, did not induce the decrease of the parasitic pressure. Changes in root growth were not an explanatory factor and the better soil conditions for plant growth did not reduce the impact of plant-parasitic nematode. Only sugarcane refinery sludge engendered overall positive effect on the banana plant, decreasing parasitic pressure and enhancing plant growth. Sugarcane bagasse and plant residues, mainly composed of lignins and cellulose, led to significant changes in nematode community structure, increasing fungivorous nematode populations and, only after bagasse supply, those of carnivorous nematodes. The compost trial showedndment that the three commercial composts produced by SITA Verde (Biogwa, Ecogwa B, Ecogwa D) and the commercial organic amendment Vegethumus (Phallipou-Frayssinet) induced a decrease of plant-parasitic nematode populations and that this control depended on banana parasitic nematode species. In this trial, the control of banana parasitic nematodes was linked to overall biomass of banana root system. The input of Ecogwa D and Vegethumus composts boosted microbivorous nematode populations, but only Vegethumus favored the fungal decomposition pathway. Last and final summary in the thesis.