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No description available.

No description available.

In this research, PCR-based detection assays were developed to detect and quantify three N. haematococca pathogenicity genes (PDA, PEP3 and PEP5) both from isolates and DNA extracted from agricultural fields with footrot history. Denaturing gradient gel electrophoresis (DGGE), gene cloning and sequencing assays were used to explore the diversity of these genes in agricultural soils. The applicability of using quantitative (real-time) PCR to quantify these genes in infected soils was validated. Furthermore, biotic and abiotic factors that interact to cause pea footrot disease in soil were also studied. Results showed that the PDA^H allele of the PDA gene, responsible for rapid demethylation of the phytoalexin pisatin, together with PEP3 and PEP5 genes promotes maximal footrot disease in peas. DGGE results showed diversity amongst PDA and PEP5 partial gene sequences amplified from agricultural soil-DNA. Partial PEP3 gene sequences showed no diversity. There was a positive correlation between numbers of pathogenic N. haematococca spores and numbers of pea pathogenicity genes in soil. Pea pathogenicity gene numbers of up to 100 per gram of soil constituted a threshold number for pea footrot infection; potentially capable of causing footrot disease of economic proportion. A disease model that included total phosphate, carbon and ammonium-nitrogen was identified with stepwise regression analysis (R² = 0.42). The PCR-based techniques developed herein are viable and reliable alternatives to culture-based assays for accurate detection and quantification of pathogenic N. haematococca in soils. They offer the opportunity for quantitative prediction of pea footrot infections in agricultural soils prior to cultivation.

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The spore germination of Botrytis cinerea and other fungi was inhibited by chloroform extracts of the leaves of three plant species, Chrysanthemum marifolium, C. parthenium, and Ribes nigrum. The inhibition was shown to be due to chemical compounds which were coextracted with the epicuticular wax of the leaves. The compounds in the chloroform extracts of leaves were found to originate from oil glands which were present on the epidermis of all three of the plant species examined. The inhibitory compounds from C. morifolium leaves were not identified. The principle antifungal compound from R. nigrum leaves was identified as sakuranetin, a flavanone aglycone, present only in the oil glands of the upper surface of the leaf. The principle antifungal compound from C. parthenium leaves was identified as parthenolide, a sesquiterpene lactone. This compound was present in extracts of both surfaces of the leaves and in the glands on the achenes. The antifungal activity of the compounds studied was found to be highly variable against B. cinerea in vitro. None of these compounds was shown to exhibit antifungal activity on the leaf surface. This was thought to be due to the compounds within the glandular structures on the leaves of C. morifolium and C. parthenium. On leaves of R. nigrum, sakuranetin was shown to be present in water droplets placed on leaves during a certain period in the development of the mature leaf. However, the inhibition of spore germination on some leaves of R. nigrum and in some droplets removed from leaves could not be attributed to sakuranetin, because of the low concentration of this compound on the leaves and in these droplets.

A polypeptide - synthesising cell-free system directed by Poly-U or Turnip Yellow Mosaic Virus-RNA was derived from imbibed seeds of Phaseolus aureus; this in vitro system was dependent upon exogenous tRNA. The Poly-U-directed system functioned in the presence of tRNAs from P.aureus, Vicia faba and yeast, whereas TYMV-RNA was translated only in the presence of tRNAs from P.aureus or V.faba. This translation barrier was related to the inability of the P.aureus high-speed supernatant enzyme fraction to charge various "protein" amino acids to yeast tRNA under uniform conditions. Such incompatibility did not exist in the Poly-U system where incubation conditions were constructed to favour only one amino acid, i.e. phenylalanine. The P.aureus enzyme fraction promoted esterification of valine to TYMV-RNA. More rigorous conditions were required for the translation of Poly-U in a Transfer System with yeast tRNA than with V.faba tRNA. Poly-U and TYMV-RNA competed for ribosomal binding sites. The characteristics of synthetic and natural templates in amino acid incorporation were correlated.

Investigators have demonstrated that the RNA from a variety of plant viruses can function as mRNA in in vitro protein synthesising systems. An active homologous plant cell-free amino acid incorporating system has been isolated from Brassica chinensis L., leaves, and partially characterised employing polyuridylic acid(poly(U)) and turnip yellow mosaic virus(TYMV) RNA as messengers. Activity of this system has been compared with an active system isolated from developing seeds of Vicia faba L., and with mixed B. chinensis - V. faba systems. Bacterial contamination was found to be low in such incubations.[14(_c)] phenylalanine aminoacylation of B. chinensis tRNA was maximal at 17.5 mM Mg(^2+) under which conditions TYMV RNA was found to accept [14(_c)] valine. Maximum [14(_c)] phenylalanine poly(U) directed incorporation occurred at 8 mM Mg(^2+) in the V. faba and 6 mM Mg(^2+) in the B. chinensis system. TYMV RNA was relatively inactive when employing a single [14(_c)] amino acid, but was active in the B. chinensis system when employing a [14(_c)] amino acid mixture (maximum incorporation at 6mM Mg(^+2) and 70 mM K(^+)Partial characterisation of TYMV RNA (and other system components) was carried out using polyacrylamide gel and analytical ultracentrifugation techniques, indicating the infectious viral RNA to have a high sedimentation coefficient (c. 33 S).Various extraction procedures of plant and viral components are discussed with reference to ease of isolation and resultant biological activity. Microsomes isolated rapidly from young B. chinensis leaves were found to be most active in amino acid incorporation. The application of these experiments to studies on biochemical aspects of the TYMV infection process are considered in the light of other work in this field. It would appear that resistance of V. faba to infection by TYMV does not reside at the ribosomal level, and that TYMV protein synthesis occurs, at least in vitro, on the '80 S' rather than the '70 S' ribosome.

It is becoming increasingly recognised that natural enemies in arable land, particularly polyphagous predators such as carabid beetles, may help to suppress populations of pests, and that appropriate management of such predators may lead to a satisfactory level of pest control. Previous work has shown that a polyphagous carabid predator, Pterostichus melanarius, is capable of affecting the spatial and temporal dynamics of slug pest populations. This project is an examination of how P. melanarius affects the survival, behaviour and dispersion of two important slug pests, Deroceras reticulatum and Arion intermedins, and how this information applies to spatial and temporal data previously obtained from the field. Deroceras reticulatum, but not Arion intermedius, elicited a variety of anti-predator behaviour in the presence of substrates previously exposed to the predator. The movements of slugs in arenas, incorporating a zone containing paper upon which the predatory beetles had previously been maintained and a control zone, were recorded at intervals. Significantly more slugs of all the size classes tested accumulated on the control half of arenas after 24 hours, with small slugs being quickest to respond. Slugs avoided paper exposed to both male and female beetles. Slugs also avoided paper exposed to another predatory carabid, Pterostichus madidus, but not to Harpalus affinis, a phytophagous carabid. Slugs did not respond to paper that had been exposed to beetles and then stored for five days prior to the test. Changes in parameters of movement of slugs when in the presence of P. melanarius chemicals were detected using a video-tracking system. These changes are consistent with a kinesis that would enable slugs to rapidly escape from areas where beetles were recently present. Despite this no changes in the rate of dispersion of D. reticulatum juveniles was detected in mini-plots previously exposed to P. melanarius. However, adult D. reticulatum reduced feeding and egg-laying and increased refuge on soil previously exposed to P. melanarius. Chemicals on the exterior of P. melanarius were isolated and two compounds were found to reduce feeding by D. reticulatum on leaf discs compared to control discs. One of these chemicals is currently being analysed using mass spectroscopy and NMR to determine it's structure and identity. It was concluded that D. reticulatum have evolved behavioural responses to chemical cues from either this generalist carabid predator in particular, or carabid beetles generally, many species of which include molluscs in their diets. During a video-tracking study of beetle movements, some evidence was found for the detection and response of beetles to slug mucus, and amputation work suggested that the palps may be important in slug detection. Previous feeding experience was found not to influence prey choice in P. melanarius during a food choice experiment, with beetles always selecting a mixed diet when offered. Analysis of spatial data showed that slug size, but not beetle sex, was important in the spatial relationship between the predator and the prey, and this agrees with results from the laboratory experiments of slug behaviour. This work has added to the evidence provided by other studies that some generalist predators can have significant effects on the dynamics of pest populations and therefore may become useful biocontrol agents for pests if effectively managed. The implications of this work in the field of predator-prey ecology and for the efficacy of P. melanarius as a biological control agent of slugs are discussed.

No description available.