Browsing by Author "Beukes, Cornelia Elizabeth"

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    Pathogenicity and mycotoxin production of the Fusarium graminearum species complex in South African grains
    (Stellenbosch : Stellenbosch University, 2015-12) Beukes, Cornelia Elizabeth; Viljoen, Altus; Rose, Lindy J. ; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Fusarium graminearum is one of the most ubiquitous Fusarium species complexes causing diseases of various grain crops worldwide. The most common grain diseases associated with the F. graminearum species complex (FGSC) include Gibberella ear rot (GER) of maize, Fusarium head blight (FHB) of small-grain cereals such as wheat and Grain Mould (GM) of sorghum. High infection rates lead to reduced seed germination, seedling blight and low kernel weight, and drastically reduced profits. Infection, furthermore, poses a health threat, as the FGSC produces toxic secondary metabolites known as mycotoxins, of which zearalenone (ZEA) and the type-B trichothecenes (TCT-B), deoxynivalenol (DON) and nivalenol (NIV), are the most common. Increasing efforts to manage the occurrence of harmful Fusarium spp. and their mycotoxins, both in commercial and subsistence farming systems, should be made. Host- pathogen relations, such as host-preference and -specificity, are important concepts when developing disease control strategies, as it affects the application of crop rotation systems, and could lead to novel approaches to achieve improved resistance in commercial cultivars. Precise measurements of fungal colonisation and mycotoxin contamination in host crops are fundamental requirements when studying diseases caused by species of the FGSC. Differences in the measured values should be consequential to the fungi screened, and not the quantification technique used. High variability in measurements of the same sample, indicating low precision, will result in unreliable results. The reproducibility and repeatability of quantitative real-time PCR (qPCR) and liquid chromatography mass spectrometry (LC- MS/MS) assays were, therefore, demonstrated for colonisation and mycotoxin deposition by FGSC species in maize, wheat and sorghum grain. The in-house validated mycotoxin analysis technique was successfully used to evaluate maize, wheat and sorghum grain grown under greenhouse conditions, following artificial inoculation with isolates of the FGSC. The validated qPCR assay was further applied to quantify fungal colonisation in the inoculated maize grain. To study host-preference by FGSC species, the pathogenicity, colonisation and mycotoxin production of five FGSC members known to occur in South African grains were tested by inoculation of maize, wheat and sorghum grain under field conditions. Higher colonisation and TCT-B production was observed by isolates of F. boothii in maize, and F. graminearum isolates in wheat. However, a selective advantage of F. boothii to cause disease on maize could not be established. Fusarium graminearum was the most aggressive FGSC species on wheat. Climatic conditions are proposed as an influential factor, as wheat was planted during the cooler winter months in this study, and F. graminearum prevalence correlates with cooler regions in global survey studies. Host preference could, therefore, neither be confirmed nor refuted and isolate-specific, rather than species-specific characteristics are proposed as an additional variable in assessing fungal colonisation and mycotoxin production in grain.