Browsing by Author "Cyster, Amore"

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    The manipulation of soil microbial composition for banana fusarium wilt management
    (Stellenbosch : Stellenbosch University, 2021-03) Cyster, Amore; Viljoen, Altus; Mostert, D.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Banana (Musa sp.) is an important food security crop especially in developing countries. Most of bananas are cultivated for local consumption and only 15% of the total banana production is traded in the international market. Approximately 50 billion tonnes of Cavendish bananas are produced globally every year. A major constrain to banana production is Fusarium wilt, which is caused by the soil- borne fungus Fusarium oxysporum f. sp. cubense (Foc). Different races of the pathogen are identified based on pathogenicity to reference host cultivars. Race 1 and Race 2 cause disease on Gros Michel and some cooking bananas like Bluggoe. Race 4 is further divided into subtropical (STR4) and tropical (TR4) and affects Cavendish and most banana cultivars susceptible to Race 1 and 2 in the subtropical and tropical regions, respectively. As mentioned, Foc is a soilborne fungus that produce thick-walled survival spores called chlamydospores. These spores are resilient in unfavourable environmental conditions and may survive in soil for more than 20 years. Once Foc is infested in a plantation, it is extremely difficult to eradicate. The only option to continue with production is to plant resistant varieties. Partially resistant somaclonal Cavendish variants to TR4 have been developed but resistance lowers as the crop cycle increases. Foc inoculum management plays a key role in this sense. The use of biological control agents for Fusarium wilt of banana have been studied for many years and reported positive results. The mode of action of biological control agents can either be direct (production of antibiotics, parasitism, or competition) or indirect (induced systemic resistance or plant growth promotion). In this study potential biological control candidates and their cell-free filtrates were investigated for its ability to suppress the growth of Foc STR4, TR4, Race 1 and Race 2 in vitro. Significant growth inhibition was reported in isolates identified as Bacillus spp. and Burkholderia sp. Greenhouse evaluations reported bacterial isolates identified as Bacillus spp, Pseudomonas sp. and Burkholderia sp. significantly reduced disease incidence and increased plant height when applied as a live cell cultures and as cell-free filtrates compared to untreated control. The use of soil amendments such as organic matter application, bio-fertilisers and urea can contribute to soil health and suppressiveness. In this study, five soil treatments were tested for their ability to suppress Foc STR4 disease and increase plant health when applied as a preventative or curative treatment. Urea, Vermicompost applied as curative treatment and Effective Microbes (EM) applied as curative treatment significantly reduced disease incidence compared to an untreated control. Urea treatment significantly decreased Foc STR4 spore counts in soil compared to an untreated control. Vermicompost significantly increased plant height and increased root mass.