Wheat bulb fly (WBF) (Delia coarctata, Fallén, Diptera: Anthomyiidae) is a pest of commercial importance in cereal crops. Control is dependent on organophosphates some of which are restricted in the UK, while current oviposition monitoring techniques are labour intensive and subjective. Eggs are not laid in association with a host-plant, therefore, prompt location of a suitable host is critical to the survival of the newly hatched larvae. Wheat bulb fly larvae have been shown to exhibit a positive chemotactic response to wheat and other host-plant seedlings and their root exudates. The objective of this study was to improve the control and population monitoring methodology associated with WBF, by investigating the ecology and specifically the chemical ecology of the WBF. Bioassays were used to investigate the behavioural response of WBF to known chemical constituents of host-plant exudates. Four secondary metabolites were found to be attractive while CO2 was found to alter the behaviour of larvae. Wheat bulb fly oviposition was assessed in field situations to describe egg laying spatially and through time. Geostatistical and ecological techniques were used to observe the spatial dependence and dispersion of oviposition and construct contour maps or scale-sized dot graphs of oviposition density. The traditional single line transect sampling pattern was compared against a more intensive sampling regime. Oviposition monitoring was conducted over a three year period to ascertain the time of peak egg density of this fly. A molecular based diagnostic test to assess WBF egg populations for damage forecasting was developed. A real time polymerase chain reaction (PCR) protocol was produced to estimate field populations of WBF eggs through the quantification of eggs from field samples. In addition endpoint PCR was used to identify the presence or absence of eggs from samples. This study gives the potential to advance current control methodology by providing the basis for the development of a lure and kill or confusion/disruption strategy, while offering a more accurate sampling system and a molecular diagnostic test, for improvement of the management of WBF.

The influence of hyperaccumulator and phytostabilizing plants on soil solution chemistry and subsequent metal dynamics in the rhizosphere was investigated to gain a better understanding of the mechanisms governing metal availability and plant uptake at the soil:root interface during phytoremediation of metal contaminated soils.

Dans l’objectif de redynamiser la culture des protéagineux, il est primordial d’améliorer la gestion du risque lié à Aphanomyces euteiches, agent responsable de la pourriture racinaire du pois. Le manque de connaissances sur les mécanismes d’infection d’A. euteiches constitue un frein à l’élaboration de stratégies de contrôle durable. Dansl’optique d’étudier les premières étapes du processus infectieux d’A. euteiches, laconstruction d’une souche A. euteiche-GFP a été entreprise. Transfecter A. euteiches aura permis d’assurer (i) la production de protoplastes par digestion enzymatique du mycélium puis (ii) d’insérer le gène gfp par la méthode de transfection chimique PEG-CaCl2 et (iii) de constater l’insertion stable du gène gfp dont l’expression s'est avérée transitoire. En parallèle, dans l’objectif d’apporter des éléments de réponses quant aux rôles des exsudats racinaires et du Root Extracellular Trap (RET) dans les réactions de défense du pois, une étude comparée des interactions entre Pisum sativum (plante sensible) et Vicia Faba (plante tolérante) au pathogène A.euteiches a été réalisée durant les premières phases de l’infection. Alors que de nombreuses variations au niveau de la composition polysaccharidique du RET et des exsudats ont été observées chez le pois, la féverole a présenté des modifications marginales. Chez le pois, l’infection est intense et rapide alors qu’elle semble réduite chez la féverole. La féverole repousse les zoospores tandis que le pois infecté les attire davantage. La féverole semble pouvoir protéger le pois au travers de mécanismes de communication qu’il convient de caractériser. L’ensemble de ces résultats semblent prometteurs dans le développement de méthode de lutte contre la pourriture racinaire du pois. Enfin, l’étude des propriétés bio-physico-chimiques des sols susceptibles de conditionner l’apparition de la maladie ont permis de confirmer la corrélation positive entre la densité d’inoculum du pathogène et le potentiel infectieux (PI) dans des sols naturellement infestés : les sols possédant des teneurs élevées en sable ou en calcium s'avèrent défavorables au développement de la maladie. Cette étude a aussi permis de mettre en évidence une influence possible des communautés microbiennes des sols, susceptibles d’influencer le processus infectieux d’A.euteiches / Aphanomyces euteiches is a pathogenic oomycete considered to be the most damaging root disease of pea crops in the world and there is currently no registered pesticide for its control. Crop management is the most efficient tool to control root rot, and avoidance of infested soil seems to be the optimal solution. Mechanisms related to A. euteiches root colonization remain poorly understood. In order to better understand A.euteiches infectious cycle, a polyethylene glycol (PEG) – calcium chloride (CaCl2) transformation protocol has been perfected in order to stably express the reporter gene GFP. The data show for the first a transient expression of green fluorescent protein (GFP) which can be observed in A.euteiches mycelium, a Saprolegnia oomycete. Vector pGFPN, containing the ham34 promoter and terminator of the Peronospora oomycete Bremia Lactucae, was introduced in A.euteiches protoplasts. Transient expression of GFP could be observed in A. euteiches mycelium by confocal microscopy. qPCR analyses confirmed the actual gfp gene insertion in its genome. Meanwhile, the influence of both pea and faba bean root extracellular trap (RET) and root exudates has been explored for A. euteiches zoospores by chemotaxis assays, microscopic observations and oomycete DNA quantification. Reciprocally pea and faba bean roots responses to A. euteiches infection have been studied at early stage of infection by biochemical analysis of cell wall polymer content in the RET and root exudates. Whereas infected pea root exudates stimulated A.euteiches zoospores attraction, faba bean exudates had a repellent effect on zoospores. In response to infection, arabinogalactan protein content of root pea exudates was altered. Interestingly, A.euteiches colonization was less intense on faba bean root surface and protect pea root at early stage of infection. Finally, the correlation between inoculum quantity in infested and the inoculum potential (IP) in field has been confirmed by qPCR. Analyses of the influence of abiotic soil parameters on the disease showed that a high calcium concentration or sand content negatively impact the IP. Furthermore, microbial communities proved to play a role in the expression of the disease in some soils. Metagenomics could be applied in order to provide new directions in managing this disease.

Phytoplankton blooms compromise the quality of freshwater ecosystems and the efficient processing of water by treatment works worldwide. This research aims to determine whether in-situ filamentous biofiltration processes mediated by living roots and synthetic filters as media can reduce or remove the phytoplankton loading (micro-algae and cyanobacteria) prior to a potable water treatment works intake. The underlying biofiltration mechanisms were investigated using field and laboratory studies. A novel macroscale biofilter with three plant species, named the "Living-Filter", installed in Farmoor II reservoir, UK, was surveyed weekly for physicochemical and biological variables under continuous flow conditions during 17 weeks. The efficiency of a mesoscale biofilter using the aquatic plant Phalaris arundinacea and synthetic filters, was tested with Microcystis aeruginosa under continuous flow conditions and in batch experiments. The 'simultaneous allelochemical method' was developed for quantifying allelochemicals from Phalaris in aqueous samples. Microscale studies were used to investigate biofilter allelochemical release in response to environmental stressors and Microcystis growth inhibition in filtered and unfiltered aqueous root exudate. Results demonstrate that the removal of phytoplankton biomass by physical mechanisms has a removal efficiency of ≤45% in the "Living-Filter" (filamentous biofilter plus synthetic fabric) and that the removal of Microcystis biomass using only biofilters was 25%. Chemical mechanisms that reduce Microcystis cell numbers are mediated by allelochemicals released from biofilter roots. Root exudate treatments on Microcystis revealed that Microcystis growth is inhibited by allelochemicals, not by nutrient competition, and that protists and invertebrates play a role in removing Microcystis. Filamentous biofilters can remove phytoplankton biomass by physical, chemical and biological mechanisms. Biofilters and synthetic filters in combination improve removal efficiency. Application of macroscale biofilters prior to potable water treatment works benefits the ecosystem. Plant properties, biofilter size to surface water ratio, and retention time must be considered to maximise the benefits of biofiltration processes.