AbstractsBiology & Animal Science

ENGLISH ABSTRACT: Fusarium verticillioides is a fungus associated with maize wherever the crop is cultivated. During its pathogenic stage the fungus causes Fusarium ear rot which manifests as pale pink, pale purple or white mycelium growth on the kernels. Fusarium verticillioides can also produce secondary metabolites known as fumonisins. The consumption of high levels of fumonisin may have detrimental effects on human and animal health. The severity of Fusarium ear rot and the level of fumonisin production are influenced by environmental conditions, insect damage and host genetics. Individual strains of the pathogen can vary in pathogenicity and fumonisin production. In this study Fusarium spp. were collected from roots, stem and kernels of maize plants in South Africa. Fusarium verticillioides was the dominant fungal species isolated, and individual isolates varied in their ability to produce fumonisins. The fumonisin production by the majority of the F. verticillioides isolates did not produce significantly different fumonisin levels when tested in vitro and in planta but all isolates were pathogenic on maize ears. The beauvericin-producing F. temperatum was identified for the first time as the second most dominant fungal species occurring on ears. Fusarium verticillioides isolates with differing fumonisin-producing abilities and virulence occur throughout South Africa which increases the risk of maize to develop severe symptoms or be contaminated with high fumonisin under favourable environmental conditions. Fusarium ear rot and fumonisin production by F. verticillioides isolates collected from different geographical localities and maize tissue was investigated. The isolates were inoculated into ears of three different maize cultivars and under different environmental conditions in three field locations in South Africa. Disease severity remained low, but fumonisin levels accumulated to above 2 ppm. The cultivars tested did not influence disease severity or fumonisin accumulation. However, when using selected F. verticillioides isolates Fusarium ear rot severity and fumonisin levels were influenced by environmental conditions and by the pathogenic and toxigenic potential of the F. verticillioides isolate used. The population genetic structure and reproductive strategy for the F. verticillioides population in South Africa were evaluated for the first time. The F. verticillioides population collected from maize roots and stems were genetically distinct from the F. verticillioides isolates from the ears. A high percentage of genotypes were shared in localities with similar climatic conditions. Both mating type genes were present in the F. verticillioides population in near equal percentages; an indication of sexual recombination that can lead to high intra-genetic diversity in F. verticillioides. Due to sexual recombination, genetic variation can be generated in the F. verticillioides population in South Africa that could complicate efforts to effectively manage the disease. AFRIKAANSE OPSOMMING: Die swam…