Evaluation of southern African maize germplasm for phytoalexin accumulation following inoculation by Fusarium verticillioides

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dc.contributor.advisorMurray, Shane Len_ZA
dc.contributor.advisorRafudeen, Suhailen_ZA
dc.contributor.authorVeenstra, Amyen_ZA
dc.date.accessioned2018-01-30T10:24:59Z
dc.date.available2018-01-30T10:24:59Z
dc.date.issued2017en_ZA
dc.description.abstractMaize is a socially and economically important crop in Africa (and worldwide) that is severely affected by many fungal pathogens. The pathogen Fusarium verticillioides causes Fusarium ear rot in maize, a disease that greatly reduces quantity and quality of annual maize yields. The pathogen produces mycotoxins called fumonisins, which have been linked to adverse health effects in both humans and animals. Maize produces terpenoid phytoalexins, which are antimicrobial compounds that directly reduce the growth of many fungal pathogens including F. verticillioides. Two families of maize phytoalexins, termed kauralexins and zealexins, have been characterized. Key genes putatively involved in the biosynthetic pathway of these phytoalexins have been identified from the rice model and subsequent studies on maize. This research aimed to evaluate the correlation between phytoalexin accumulation and fungal growth in diverse southern African maize lines in response to F. verticillioides inoculation. Maize lines were inoculated with F. verticillioides using a seed soak inoculation method and grown in vitro for up to two weeks. The harvested tissue was analysed for fungal growth using quantitative PCR, putative phytoalexin biosynthetic gene expression using RT-qPCR and phytoalexin accumulation using gas-chromatography mass spectrometry. Furthermore, an endophyte growing in one of the maize lines was isolated and identified as Trichoderma asperellum. Trichoderma spp. are used as biocontrol agents against many fungal pathogens, although research on the specific antagonistic effect of T. asperellum on F. verticillioides is limited. Phytoalexin accumulation in maize containing endophytic T. asperellum was compared to maize inoculated with F. verticillioides. In vitro competition assays were performed to analyse the antagonistic effect of T. asprellum on F. verticillioides. Results from this study show that inoculation of maize lines with F. verticillioides induces the accumulation of total phytoalexins, and more specifically the accumulation of total kauralexins. Putative phytoalexin biosynthetic genes are also up-regulated in response to inoculation. Maize growing with a T. asperellum endophyte accumulated phytoalexins to the same levels as F. verticillioides, suggesting that T. asperellum induces a defence response that 'primes' the plant for further infection. In vitro competition assays between F. verticillioides and T. asperellum showed that T. asperellum significantly inhibits F. verticillioides growth. These results will aid in the identification of maize lines that can be bred with increased resistance to F. verticillioides with the goal to reduce F. verticillioides incidence in southern Africa. Furthermore, analysis of the efficacy of T. asperellum as an antagonist against F. verticillioides may provide another method for disease reduction in the field.en_ZA
dc.identifier.apacitationVeenstra, A. (2017). <i>Evaluation of southern African maize germplasm for phytoalexin accumulation following inoculation by Fusarium verticillioides</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Molecular and Cell Biology. Retrieved from http://hdl.handle.net/11427/27095en_ZA
dc.identifier.chicagocitationVeenstra, Amy. <i>"Evaluation of southern African maize germplasm for phytoalexin accumulation following inoculation by Fusarium verticillioides."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Molecular and Cell Biology, 2017. http://hdl.handle.net/11427/27095en_ZA
dc.identifier.citationVeenstra, A. 2017. Evaluation of southern African maize germplasm for phytoalexin accumulation following inoculation by Fusarium verticillioides. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Veenstra, Amy AB - Maize is a socially and economically important crop in Africa (and worldwide) that is severely affected by many fungal pathogens. The pathogen Fusarium verticillioides causes Fusarium ear rot in maize, a disease that greatly reduces quantity and quality of annual maize yields. The pathogen produces mycotoxins called fumonisins, which have been linked to adverse health effects in both humans and animals. Maize produces terpenoid phytoalexins, which are antimicrobial compounds that directly reduce the growth of many fungal pathogens including F. verticillioides. Two families of maize phytoalexins, termed kauralexins and zealexins, have been characterized. Key genes putatively involved in the biosynthetic pathway of these phytoalexins have been identified from the rice model and subsequent studies on maize. This research aimed to evaluate the correlation between phytoalexin accumulation and fungal growth in diverse southern African maize lines in response to F. verticillioides inoculation. Maize lines were inoculated with F. verticillioides using a seed soak inoculation method and grown in vitro for up to two weeks. The harvested tissue was analysed for fungal growth using quantitative PCR, putative phytoalexin biosynthetic gene expression using RT-qPCR and phytoalexin accumulation using gas-chromatography mass spectrometry. Furthermore, an endophyte growing in one of the maize lines was isolated and identified as Trichoderma asperellum. Trichoderma spp. are used as biocontrol agents against many fungal pathogens, although research on the specific antagonistic effect of T. asperellum on F. verticillioides is limited. Phytoalexin accumulation in maize containing endophytic T. asperellum was compared to maize inoculated with F. verticillioides. In vitro competition assays were performed to analyse the antagonistic effect of T. asprellum on F. verticillioides. Results from this study show that inoculation of maize lines with F. verticillioides induces the accumulation of total phytoalexins, and more specifically the accumulation of total kauralexins. Putative phytoalexin biosynthetic genes are also up-regulated in response to inoculation. Maize growing with a T. asperellum endophyte accumulated phytoalexins to the same levels as F. verticillioides, suggesting that T. asperellum induces a defence response that 'primes' the plant for further infection. In vitro competition assays between F. verticillioides and T. asperellum showed that T. asperellum significantly inhibits F. verticillioides growth. These results will aid in the identification of maize lines that can be bred with increased resistance to F. verticillioides with the goal to reduce F. verticillioides incidence in southern Africa. Furthermore, analysis of the efficacy of T. asperellum as an antagonist against F. verticillioides may provide another method for disease reduction in the field. DA - 2017 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2017 T1 - Evaluation of southern African maize germplasm for phytoalexin accumulation following inoculation by Fusarium verticillioides TI - Evaluation of southern African maize germplasm for phytoalexin accumulation following inoculation by Fusarium verticillioides UR - http://hdl.handle.net/11427/27095 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/27095
dc.identifier.vancouvercitationVeenstra A. Evaluation of southern African maize germplasm for phytoalexin accumulation following inoculation by Fusarium verticillioides. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Molecular and Cell Biology, 2017 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/27095en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Molecular and Cell Biologyen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherMolecular and Cell Biologyen_ZA
dc.titleEvaluation of southern African maize germplasm for phytoalexin accumulation following inoculation by Fusarium verticillioidesen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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