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Title: Identification of microbes degrading nematicides and the development of a diagnostic assay for nematicide persistence in soils
Author: Osborn, Rachel Kathleen
ISNI:       0000 0001 3460 3406
Awarding Body: Open University
Current Institution: Open University
Date of Award: 2005
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The potential for enhanced degradation of the carbamate nematicides oxamyl and aldicarb was demonstrated in UK agricultural soils by applying three successive applications in laboratory incubation. Enhanced degradation was observed in all of the soils treated with oxamyl except one, soil OX 11. The reason for the comparatively slow rates of degradation in this soil could not be explained by any physical property of the soil. Enhanced rates of degradation were recorded for nine of the fifteen soils treated with aldicarb. The rate of aldicarb degradation did appear to be affected by low pH and high organic matter content. Enhanced degradation of the organophosphorus nematicide fosthiazate was not observed in any of the ten soils investigated. This was the case irrespective of soil type, pH, organic matter or nematicide-treatment history. Enhanced degradation of oxamyl was also observed in liquid media containing oxamyl as the sole carbon source. Thirty-six oxamyl-degrading bacteria from seven different soils were characterised by partial 16S rRNA sequence analysis. Twenty-one of these strains showed high similarity to Aminobacter aminovorans, 14 demonstrated an equal degree of similarity to the species A. niigataensis and Chelatobacter heintzii and one was classed as a Mesorhizobium sp. Using mcd gene specific primers to detect mcd gene homologous sequences resulted in the visualisation of mcd gene sized bands, under gel electrophoresis, for ten of the 28 isolates tested. An investigation into the suitability of the enrichment culture method for predicting the potential for enhanced degradation of nematicides in agricultural soils gave promising results. The enrichment culture method mirrored the enhanced degradation results of the incubation study in nine of the 19 soils tested, i.e., enhanced degradation occurred in both the incubation and the enrichment study or it was absent from both. The method was, however, found to be less reliable in low pH soils.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Nematicides