The literature on the relation of uncultivated land to crop pests is reviewed with a distinction between biological and physical relations. A description of preliminary experiments demonstrating types of relationship suitable for quantitative work is followed by an account of the techniques used in a two year study of Cabbage Aphid (Brevicoryne brassicae L.) infestation of cultivated crucifers. The progress of this infestation in both seasons is traced on a basis of the aphid's life history, and the factors affecting the aphid populations are discussed. Nutritional factors are considered of major importance. The edgegrowch is assessed as a parasite and predator reservoir and, in the crop, the edges and centre of the field are compared in respect of edgegrowth effects. Physical effects of shelter on the growth of the host plant and the adverse effects on the aphid's reproductive rate are discussed; also the deposition of aphids from air currents. Heavy predation at the open edges is considered due partly to the invasion of predators from the edgegrowth and partly to heavier oviposition by Syrphidae near flowers which provide food for the adult females. Conclusions are given on the general role of uncultivated land in a pest infestation of a crop, with particular reference to the pest species studied and the strips of edgegrowth immediate to the crop.

Modern agriculture couples the management of invasive weed species with enhancing crop yields through the intensive use of herbicides. As a result of herbicides being the primary method of weed control in agronomic crops, herbicide resistance has evolved and there has been a vast increase in the occurrence and distribution of herbicide resistant weeds. Many of the most problematic weeds have now evolved multiple herbicide resistance (MHR), which is associated with an enhanced ability to detoxify xenobiotics, enabling the weed to survive herbicide application irrespective of the mode of action. As herbicide resistance is a major limiting factor to food security in global agriculture, effective methods for weed management are sought. This work focuses on MHR in black grass (Alopecurus myosuroides), one of the most damaging weeds of winter cereals. Previous work by Edwards et al. described that black grass populations showing MHR, exhibit an upregulation in the expression of a specific phi-class glutathione transferase (AmGSTF1), which is thought to have a direct regulatory control on metabolism. The importance of AmGSTF1 in MHR has been confirmed both genetically by transgene experiments and chemically through inhibition experiments. This offers the opportunity to develop potential herbicide synergists, which are active towards AmGSTF1 and restore herbicide control in multiple herbicide resistant black grass. Considering the rapid spread of MHR in grass weeds and the limited development of new herbicides, synergists offer an important alternative strategy in counteracting resistance in the field. Recently a new class of AmGSTF1 inhibitors, derived from flavonoids, could be identified. Initial efforts focused on the synthesis of a series of flavone analogues, mainly with structural changes of the C-ring and different substituents in the 5-position. A particular emphasis was put on increasing the aqueous solubility and other physicochemical properties of the compounds, in order to increase the bioavailability in the plant. Although the potency of the initial lead molecule could not be increased in vitro, 5,7-dimethoxy-2-(1’,3’-thiazol-2’-yl)-4H-chromen-4-one, with a significantly increased aqueous solubility, showed good results in in vivo studies in black grass and acted as a synergist to the herbicide pinoxaden. The black grass plants died, when pinoxaden (10μl of a 15 μM solution) was applied to plants, which were pre-treated with the thiazole (10 μl of a 2 mM solution), but survived the herbicide treatment, if no synergist was applied prior.

No description available.

No description available.

Aphids harbour symbiotic bacteria that can have positive, negative or neutral effects on their survival and performance. These bacteria are split into two groups: the primary obligate endosymbiont, Buchnera aphidicola, and the secondary ‘facultative’ bacteria. In pea aphid (Acyrthosiphon pisum) three vertically transmitted secondary facultative bacteria have been shown to influence various fitness traits in their aphid hosts, including susceptibility to natural enemies. Very little is known however, about the fitness effects of bacterial associations in other aphid species. The aim of this study was to characterise bacterial diversity in a Scottish arable pest, the cabbage aphid (Brevicoryne brassicae), and investigate whether bacterial composition influences trophic interactions by testing their impact on aphid–parasitoid interactions. The bacterial community of cabbage aphid was quite different to pea aphid, both in terms of the density of the primary symbiont, Buchnera, but also in secondary bacterial complement. There was a wide diversity of bacteria associated with the cabbage aphid although these were not the three commonly studied pea aphid secondary symbionts and were likely to be a different type of symbiont, relying primarily on horizontal transmission. Phylogenetic analysis of 16S sequence revealed that the majority of bacterial types could be split into two groups: Group 1 Pseudomonas type bacteria and Group 2 Erwinia type bacteria. A real-time (Taqman®) qPCR assay was used to determine the infection status of the cabbage aphid lines and indicated there were four different community types in cabbage aphid: (1) aphid lines dominated by Group 1 bacteria; (2) aphid lines dominated by Group 2 bacteria; (3) aphid lines that harboured large approximately equal amounts of each group of bacteria; (4) aphid lines that harboured relatively little of either group of bacteria. The molecular results provided a basis for aphid–parasitoid fitness experiments. Preliminary results, based on single aphid genotypes, indicated that harbouring Group 2 Erwinia bacteria had both direct and indirect fitness costs by reducing cabbage aphid fitness and positively influencing the fitness of emergent Diaeretiella rapae parasitoids. The extent to which bacterial associations can influence aphid fitness and the truly multitrophic nature of cabbage aphid population dynamics in arable systems are highlighted by this study.

Techniques were developed to assess germplasm from wild and commercial brassica accessions for host plant resistancet o Aleyrodesp roletella. Several wild accessionsp ossessedr esistancei n both laboratory and field experiments. Most varietal differences in preference for Brassfca oleracea cultivars were due to the host plant morphology. Resistance conferred by glossy leaves was quantitatively shown for the first time. Laboratory studiess howedt hat resistancein B. incana andB . villosa was based on an antixenotic mechanism conferred by dense downy hairs which significantly reduced oviposition. Resistance in B. spinescens and B. fruticulosa was based on an antibiotic mechanism which significantly reduced the life span of adult whiteflies and increased the mortality of the larval stages. The feeding of A. proletella was assessedu sing electrical penetration graph techniques. Feeding duration was shorter on B. fruticulosa than the susceptible control. In addition, A. proletella styletsd id not penetratem esophylcl ells,t he importanceo f this in relationt o virus transmission is discussed. Stylet activity of larval whiteflies was greater on both B. spinescens and B. fruticulosa than a susceptible control indicating problems in finding or remaining within the phloem. Some aspects of the relations between larval whiteflies and their hosts are discussed

Blast disease of wheat has emerged as a new and serious field disease affecting wheat production in South America. The causal agent of wheat blast, Magnaporthe oryzae, infects cultivated crops including rice, wheat and barley, while M grisea is adapted to infect wild grass species. Durable disease resistance of crops against fungal pathogens may be achieved through non-host resistance; which is defined as resistance of a plant species to a non-adapted pathogen. Cellular defence responses and transcriptional changes of wheat cv. Renan, infected with adapted and non-adapted isolates of Magnaporthe spp., were investigated. Appositions formed beneath attempted penetration sites appeared to prevent colonisation by the nonadapted M grisea isolate, but were breached by the adapted M oryzae isolates. Microarray analysis indicated that wheat undergoes extensive transcriptome reprogramming following inoculation with both adapted and non-adapted isolates of Magnaporthe spp. A distinct set of transcripts were induced exclusively in response to the non-adapted M grisea isolate, while others were induced in response to both adapted and non-adapted isolates. Defence-related transcripts induced in common by adapted and non-adapted isolates were differentially regulated in response to M oryzae and M grisea isolates over time. Establishment of a virus induced gene silencing (VIGS) system in wheat cv. Renan enabled functional analysis of differentially expressed transcripts. Silencing the gene WIRT increased cell-to-cell spread of M oryzae hyphae, but not penetration efficiency, suggesting a postpenetration resistance role for this gene. Another gene, TaNIN was induced at early time points in response to both adapted and non-adapted Magnaporthe isolates. A partial sequence of this gene was cloned and shown to be the first nodule inception (NM-like gene characterised in wheat. This study provides an insight into the development of Magnaporthe spp. on wheat, together with functional characterisation of transcripts differentially expressed during adapted and nonadapted Magnaporthe spp. -wheat interactions.

In agroecosystems, conservation biological control is often constrained by low availability of pollen and nectar. Although floral resources can be integrated into agricultural systems, this usually requires sacrifice of productive land. This thesis describes experiments which test the influence of floral resources provided by species which have marketable value in their own right as food or medicinal crops. Floralresource strips comprising such species were intercropped with Brassica crops at plot, field and commercial scales in replicated field experiments. The abundance and distribution of key Brassica crop pests a,nd their natural enemies in the presence of floral resources was examined. Parasitoids displayed distinct flower species preferences; Fagopyrum esculentum significantly increased parasitoid abundance. Parasitoids also responded to distance; their abundance significantly declined with increasing distance from floral strips, especially in F. esculentum, and parasitism levels declined significantly after 8 m. Borago offtcinalis also proved attractive to parasitoids and Tanacetum parthenium to Syrphidae. In addition, F. esculentum and B. offtcinalis were found to suppress the second generation of Pierid larvae at field scale. This evidence suggests that several flower species could be intercropped within a Brassica crop to promote biological pest control.

No description available.

Elicitation, a successful strategy for overproduction of secondary metabolites has been reported in plant, fungal and filamentous bacteria. Based on this evidence, elicitation was assessed for its potential to enhance antibiotic production in Bacillus cultures. This work reports, for the first time, the effect of oligosaccharide elicitors, concentration and addition time through optimisation studies for the enhancement of bacitracin A production by Bacillus licheniformis cultures. The optimal elicitor type, addition time and concentration was 100 mg L-1 of oligoguluronate (OG) at 24 hours. Different carbohydrate- based elicitors were used to investigate their effect on reactive oxygen species (ROS) and catalase production in B. licheniformis. Changes in ROS levels were observed when cells were challenged with OG and MO (mannan oligosaccharides) at 24 h and 72 h. Catalase activities were 50% and 43% higher in OG and MO supplemented cultures respectively compared to the control cultures. The effect of optimal single (OG: 100 mg L-1 , 24 h) and multiple (OG: 100 mg L-1 , 0 h; MO: 200 mg L-1 , 24 h) elicitor addition to enhance bacitracin A production in B. licheniformis cultures was studied. HPLC results demonstrated an increase of 37% and 23% in bacitracin A production in multiple and single elicitor addition respectively compared to control cultures. The effect of elicitors was also investigated at the transcriptional level for bacitracin biosynthetic bacABC and ABC transporter bcrABC genes. Absolute real-time PCR results revealed higher transcript levels of bacABC and bcrABC in elicitor-added cultures compared to control cultures. A relationship between the enhanced bacitracin A production and the increased bacABC and bcrABC transcript copy numbers was found. Stirred tank reactor fermentation with controlled pH (7.0), increased the production of bacitracin A by 30% compared to fermentations without pH regulation. The addition of the oligosaccharides to the cultures caused increases in carbon dioxide evolution rate, oxygen uptake rate, ATP levels, L-glutamic acid consumption rate and bacitracin A production compared to the control cultures. Intracellular calcium levels in bacterial cultures were measured by the use of aequorin technology. Addition of OG and MO caused 11 and 7 fold increases in cytosolic calcium levels in Escherichia coli. Fold increases of 10 and 3 were also observed with OG and MO supplementation to B. subtilis cultures, respectively. Addition of different elicitors also resulted in different calcium signatures which could be used to transmit specific signals inside the cell. Measurement of intracellular calcium levels in B. licheniformis cultures was unsuccessful and awaits further studies. Events involved in the elicitation of B. licheniformis cultures were presented and put together to bring forward the elucidation of the mechanism of elicitation in bacterial cultures. Understanding of the mechanism of elicitation would help in its application in other microbial systems, potentially providing economical benefits to biotechnological industries.