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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Peronospora viciae pre-invasion development : a proteomic analysis

Wandji, Josiane Laure Chuisseu January 2010 (has links)
The proteome of Peronospora viciae, an obligate biotrophic pathogen that causes downy mildew of pea (Pisum sativum), was investigated using 2D gel electrophoresis and mass spectrometry. This provided data on changes in protein abundance during the sequential development of pre-invasion stages, from un-germinated conidia to germinated conidia with germ tubes and appressoria. Preliminary work developed reproducible methods for in vitro germination of conidia through to appressorium development. The method developed for in vitro conidia germination resulted in up to 65% of germinated conidia, of whi ch 35% fonned an appressorium. Six methods for protein extraction from the pre-invasion stages were compared by ID and 2D SDS-PAGE electrophoresis. The method chosen had relatively simple and non -toxic constituents (urea, thiourea, CHAPS and Tris-HCl), and would be appropriate for use in a disposable diagnostic device. Gels of extracted proteins showed over 700 protein spots following Coomassie blue staining of 2D gels and over 2000 protein spots on difference gel electrophoresis (DIGE) gels. A total of 21 proteins were identified from P. viciae using MALDI - and Q-TOF mass spectrometry analysis and searching against the MASCOT databases. Of the identified proteins, the majority (2 Hsp 70, a succinate dehydrogenase, an enolase, a catalase, a S-adenosyl-L-methioninedependent methyltransferase, a Hsp72, 2 actins, three GAPDH, a Fructose-bisphosphate aldolase, a fatty acid phospholipid synthesis protein, an uncharacterized aldolase, a Protein CpnIO and a NDK) decreased in relative abundance during spore germination, but with no further change on fonnation of appressoria. In contrast, the relative abundance of calmodulin and chitin synthase remained constant throughout pre-invasion development. However, calmodulin was not detected using western blotting whereas isoforms of actin and GAPDH were detected. Data are interpreted in relation to P. viciae pre-invasion biology, and the identification of key proteins and biomarkers as novel targets for control, pathogen detection and disease diagnosis.
2

The mechanism of infection of potatoes by Oospora pustulans causing skin spot

El-Nagdy, G. E. A. January 1963 (has links)
No description available.
3

Aspects of the etiology of pink rot of the potato

Wynn, A. R. January 1981 (has links)
Phytophthora erythroseptica, the causal agent of pink rot of potato was found to produce more sporangia with non-sterile soil extract than with Petri's solution. Centrifugation of the growth medium above 3,000 £ reduced the number of sporangia formed, whilst low intensity light at all wavelengths except ultraviolet light (300-400 nm) was stimulatory to sporangial production. Zoospores of the fungus were shown to be attracted to low concentrations of ethanol under laboratory conditions though this was not observed in the field. Germination of oospores of P. erythroseptica was variable and differences between naturally produced and culture-produced oospores were recorded. Activation, a prerequisite for germination was increased by incubation in blue light and by exposure to low temperature, though germination was highest at 20°C under white light. Germination was not stimulated by heat treatment, addition of various chemicals, the carbon source of the media or root exudates. However, continuous washing of oospores with water substantially increased germination particularly of oospores isolated from plant " tissue. Treatment of oospores with enzymes increased germination, snail gut enzyme being most stimulatory. Oospores recovered after passage through the. gut of the greyffield. slug, Doraceros reticulatus, were able to germinate immediately., A relationship between slug damage and pink rot was noted though cause and effect could not be determined. Oospores were shown to be parasitised by a large range of microorganisms in soil, with Chytridiomycetes most numerous in waterlogged soils and Hyphomycetes most numerous in drier soil. Levels of up to 36% parasitism were recorded in some soils, and the implications of this on the population of P. erythroseptica propagules is discussed. The level of inorganic nitrogen did not affect disease incidence, though water availability was shown to be necessary for disease development. Control of pink rot was achieved using the new group of acylalanine fungicides, with Metalaxyl proving most effective at 5.0 kg ai/h. The implications for future control of the disease are discussed.
4

Analysis of the mucin-like genes in the interaction between Meloidogyne incognita and Pasteuria penetrans using RNAi

Khan, Junaid Ali January 2013 (has links)
Root knot nematodes (Meloidogyne spp.) are polyphagous pests for many agricultural crops and are need to be controlled. Pasteuria penetrans is an obligate bacterial parasite of root-knot nematodes and endospores of the bacterium have been deployed as an environmentally benign biocontrol agent for these pests. However, the variability in host-specificity of Pasteuria is the contributing factor for its application. The adhesion of endospores which is the primary step of parasitism is therefore the key to understand the Velcro-like mechanism involving carbohydrate-protein interactions. Surface coat carbohydrates have been shown to effect pathogenesis of Caenorhabditis elegans. Mucins are a family of highly glycosylated proteins found on the surface coat of animal parasitic nematodes involved in the evasion of host immunity. Mucins in C. elegans have been shown to affect the recognition of its surface coat by lectin recognitions. To test the hypothesis that mucins of infective stage juveniles (J2s) of plant parasitic nematodes are involved in the attachment of Pasteuria endospores to the surface cuticle a series of experiments were carried out The orthologues to mucin-like genes from C. elegans were identified in M. incognita amplified by PCR, cloned, sequenced and dsRNA was synthisised by in-vitro transcription.
5

Studies in the storage rots of potatoes caused by Phoma species

Malcolmson, J. F. January 1951 (has links)
No description available.
6

Sources and mechanisms of host plant resistance to the cabbage whitefly, Aleyrodes proletella (L.), in brassicas

Ramsey, Andrew David January 1998 (has links)
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
7

Cellular and molecular defence responses of wheat to adapted and non-adapted magnaporthe species

Tufan, Hale Ann January 2009 (has links)
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.
8

Cross-crop benefits : developing crop combinations to promote conservation biological pest control

Key, Georgina January 2013 (has links)
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.
9

A study of Pseudomonas, with special reference to species pathogenic to stone fruit trees

Paton, A. McE. January 1956 (has links)
No description available.
10

Elicitation studies for enhanced production of bacitracin A by Bacillus licheniformis cultures

Murphy, Tania Marcela January 2008 (has links)
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.

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