Browsing by Author "Jacobs, Carlynn Melissa"

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    Evaluation of foliar fungicides for the control of mycotoxigenic fungi associated with Fusarium head blight of wheat in South Africa
    (Stellenbosch : Stellenbosch University, 2021-03) Jacobs, Carlynn Melissa; Rose, Lindy J. ; Viljoen, Altus; Van Coller, Gert J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Wheat (Triticum aestivum L.) is considered one of the most important cereal grains constrained by the fungal genus Fusarium, globally as well as in South Africa. Fusarium species are the causal organisms of Fusarium head blight (FHB), an economically important disease that results in significant yield and grain quality losses. These plant pathogens are also known to produce secondary metabolites called mycotoxins that further reduce grain quality, but also induce foodborne intoxication in humans and animals when contaminated grain is ingested. Trichothecene type B mycotoxins, especially deoxynivalenol (DON), is important in South Africa as it is predominantly associated with commercially produced wheat. Management practices to reduce FHB and mycotoxin accumulation depends on factors like agronomical practices, resistant cultivars, and the use of fungicides. To date, there are no fungicides registered for the control of FHB in South Africa, yet fungicides are extensively used in wheat production. Therefore, this study aimed to determine the potential of foliar fungicides, currently used in South Africa’s wheat production, to reduce FHB and mycotoxin accumulation. Fungicides evaluated in this study included Folicur (tebuconazole), Prosaro (prothioconazole + tebuconazole) and Abacus (pyraclostrobin + epoxiconazole). Initially the effect of these fungicides was tested in vitro at different concentrations while three agar-based assays were used to assess the sensitivity of Fusarium and Alternaria pathogens. Following this optimisation, the fungicide sensitivity of three Fusarium species was determined on a population of 25 isolates per species. The sensitivity of isolates, based on the effective concentration (EC50 and EC90) values, differed significantly (P<0.05) for each species and fungicide tested. Fusarium graminearum was the least sensitive to prothioconazole + tebuconazole with EC50 and EC90 values ranging from 0.51 ppm to 2.35 ppm while F. pseudograminearum was the least sensitive to both tebuconazole [EC50:0.96 ppm and EC90: 3.07 ppm] and pyraclostrobin + epoxiconazole [EC50:1.82 ppm and EC90:51.3 ppm]. Overall, prothioconazole + tebuconazole showed the best efficacy in reducing fungal growth of FHB pathogens. Significant differences of fungicides on mycotoxin production were also obtained. A significant cultivar x fungicide interaction was determined for all FHB disease parameters measured in the greenhouse trial while a significant fungicide x cultivar x treatment interaction was determined for the field trial. Generally, the application of fungicides significantly decreased FHB incidence, decreased the percentage Fusarium-damaged kernels and increased the thousand kernel weight of most wheat cultivars evaluated. The results of the study provide support for the use of commercial foliar fungicides that can additively contribute to the management of FHB and mycotoxin contamination.