Control of soil borne potato pathogens using Brassica spp. mediated biofumigation

Taylor, Fiona Isabelle (2013) Control of soil borne potato pathogens using Brassica spp. mediated biofumigation. PhD thesis, University of Glasgow.

Abstract

Biofumigation is being increasing used as alternative control method for soil borne pathogens. This method exploits toxic compounds, specifically isothiocyanates (ITCs), which are released during the breakdown of Brassica plant tissues. To date field and glasshouse experimentation assessing the potential for using biofumigation to control agricultural pests and pathogens have produced promising results. Yet large gaps still remain in the specifics of the biofumigation process. It is hoped that further research to analyse how specific toxic compounds produced during Brassica tissue breakdown, specifically ITCs, affect different pathogens. Additionally analysis of the specific isothiocyanates and concentrations produced by Brassica spp. will allow a more pathogen targeted approach to biofumigation to be generated. The importance of assessing the biofumigation process on different scales is also understood, and therefore this study has encompassed work carried out in vitro and using glasshouse experimentation to establish a comprehensive overview of the biofumigation process. Assessing the effects different agricultural treatments have on soil microbial communities has also been recognised and therefore was also be investigated in this study.

This study aimed to determine the effects isothiocyanates, produced by Brassica spp., have on three economically important soil borne fungal pathogens, Colletotrichum coccodes, Rhizoctonia solani and Helminthosporium solani. Initial assessment was carried out using in vitro bioassays, allowing assessment of the overall toxicity of each ITC. Results identified that the pathogen response was dependent on both the structure of the ITC and the concentration of ITC present. The most significant pathogen suppression was observed with R. solani when exposed with benzyl or methyl ITC and H. solani when exposed to 2-phenylethyl ITC.
To gain understanding of the naturally produced ITCs Gas-Chromatography Mass-Spectrometry analysis was used to analyse specific isothiocyanates produced by a range of different Brassica spp., at different development stages. Results identified Allyl, Benzyl and 2-Phenylthyl ITC as the most commonly produced by the Brassica cultivars used within this study. Overall the Allyl was found within the highest concentrations; however the specific ITCs and concentrations produced were dependent on both the development time and cultivar.

Glasshouse experimentation was also carried out to assess both the effects of pure ITCs on R. solani and C. coccodes fungal inoculum within compost and diversity changes within the soil microbial community, in response to isothiocyanate incorporation and the biofumigation process. In order to examine changes in microbial communities‟ analysis was carried out using Terminal Restriction Fragment Length Polymorphism, a DNA fingerprinting method which allows bacterial diversity shift to be traced and statistically analysed. Overall incoproation of pure ITCs did not significantly reduce black scurf or black dot disease symptoms on daughter potato tubers. Additionally
after 30 days soil microbial community diversity was not greatly altered by the addition of ITCs. Therefore as it is often suggested that biofumigation is influenced by the soil activity it is thought that this may be due to the addition of Brassica tissue. The increase of organic matter into agricultural soils may influence both biological and chemical processes which may in turn aid pathogen suppression.

Overall this study provides a detailed insight into establishing the specific interactions that occur during biofumigation. Results produced findings of ITCs which significantly suppressed the growth of fungal potato pathogens. Development of a novel GC-MS assay revealed previously unknown data of levels and profiles produced by a number of different Brassica plants. Additionally study was also carried out to evaluate the effects of biofumigation of soil microbial communities, which is often ignored within other studies. Overall this study aimed to gain an increased level of knowledge of such processes in order for the methods and the results presented, to be used to establish effective, pathogen targeted biofumigation systems.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: biofumigation, potato pathogens, potatoes, brassicas, isothiocyanates, integrated pest management, Rhizoctonia solani, Colletotrichum coccodes, Helminthosporoium solani, black dot, black scurf, silver scurf, alternative control, soil borne pathogens, soil microbiology
• Subjects: Q Science > QH Natural history > QH301 Biology; Q Science > QR Microbiology; S Agriculture > S Agriculture (General)
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Molecular Biosciences > Molecular Biosciences
• Supervisor's Name: Rosser, Prof. Susan and Kenyon, Dr. David
• Date of Award: 2013
• Depositing User: Miss Fiona Taylor
• Unique ID: glathesis:2013-4854
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 30 Jan 2014 11:24
• Last Modified: 31 Jan 2014 09:08
• URI: https://theses.gla.ac.uk/id/eprint/4854