Masters Degrees (Plant Pathology)
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Browsing Masters Degrees (Plant Pathology) by Author "Cassiem, Asheeqah"
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- ItemEffect of phenolic compounds on maize ear rot pathogens and their associate mycotoxins(Stellenbosch : Stellenbosch University, 2018-12) Cassiem, Asheeqah; Rose, Lindy J. ; Viljoen, Altus; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.ENGLISH ABSTRACT: Maize (Zea mays L.) is one of the most important staple food crops in South Africa. It is significantly affected by Fusarium ear rot (FER) pathogens such as F. verticillioides, F. proliferatum and F. subglutinans, as well as Gibberella ear rot (GER) pathogens such as F. boothii and F. graminearum which results in poor grain quality and yield. Grain contamination with these pathogens also poses a significant food safety concern, as they are known to produce mycotoxins. Mycotoxins have been associated with a number of humans and animal diseases. Mycotoxins persist during food processing as they are heat-stable molecules and thus not fully eliminated. Therefore, the most effective way to prevent mycotoxins contamination would be to limit their production and accumulation in the field. Numerous cultural methods may reduce Fusarium inoculum, however, none of these methods are totally effective under high disease pressure and ideal circumstances for mycotoxin production. Phenolic compounds, naturally produced by plants, have been shown to reduce the growth and mycotoxin production of Fusarium spp. Pre-existing phenolic compounds can act as a physical barrier to pathogens, while induced phenolic compounds have been known to accumulate in response to biotic stress such as fungal infections. Phenolic compounds are associated with plant defence mechanisms and can be seen as a potential management strategy. In this study, the phenolic compounds vanillic, ferulic, caffeic, coumaric, chlorogenic and sinapic acid were used at different concentrations (0; 0.5; 1.5 and 2.5 mM) in vitro to evaluate the effect of phenolic compounds on FER and GER causal pathogens. A significant isolate by compound by concentration interaction was observed. The growth study illustrated significant reduction in growth of all Fusarium species evaluated. The growth of all isolates was inhibited by ferulic acid (2.5 mM). Ferulic acid combined with caffeic acid did not differ significantly from ferulic acid (2.5 mM) individually, while ferulic acid combined with chlorogenic acid had a synergistic effect when compared to the compounds individually. The biomass of the FER pathogens were reduced by caffeic acid while vanillic and coumaric acid reduced the biomass of the GER pathogens. Several phenolic compounds were able to reduce the production of mycotoxins, with chlorogenic acid significantly reducing the production of all mycotoxins evaluated. Phenolic profiles in response to infection by F. verticillioides, over kernels maturation stages, of a resistant (CML 390) and susceptible (R2565y) maize inbred line was evaluated. Ferulic and caffeic acid was found at higher concentrations in the susceptible line than in the resistant line. Moreover, higher concentratrions of ferulic, sinapic and caffeic acid was observed in the water-inoculated grain of both lines compared to the fungal-inoculated grain.. No clear differences in phenolic content were established in the fungal-inoculated grain of both lines. In addition, gene expression of phenylalanine ammonia lyase (PAL) 3 was determined by reverse transcription quantitative PCR. The susceptible line displayed a delayed response to infection as PAL3 was only upregulated at 28 days after inoculation (dai). However, the resistant line illustrated a much faster defence response as PAL3 was up-regulated from 7 dai. The information obtained in this study could be used to enhance integrated disease management strategies to prevent infection by mycotoxigenic fungi and subsequent contamination with mycotoxins.