Masters Degrees (Microbiology)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/3626

Browse

Browsing Masters Degrees (Microbiology) by Subject "Agricultural pollution"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    The presence of faecal pollution, and potential plant pathogens associated with onion production, in the Lower Vaal River
    (Stellenbosch : Stellenbosch University, 2015-03) Meyer, Veronique Jane; Botha, Alfred; Viljoen, Altus; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Industrial and sewage pollution of the Vaal River pose a threat to sustainable agriculture along the Lower Vaal River in the Northern Cape of South Africa. In this region, the Vaal River is used to irrigate onion fields via centre-pivot irrigation systems. However, irrigation water originating from rivers may, in addition to human pathogens, contain waterborne plant pathogens that are washed into river systems by agricultural surface runoff, posing a threat to crop production. Thus, the goals of this study were firstly to screen for both faecal contamination in the Lower Vaal River, as well as the onion pathogen Fusarium oxysporum f. sp. cepae (Focep). Subsequently, the efficacy of a calcium hypochlorite containing disinfectant, i.e. „HTH® Super Shock It‟, was determined to remove coliform bacteria and Fusarium spores from the river water within 16 s. This is the contact time allowed for a disinfectant when water is treated at the hub of a centre-pivot irrigation system, before it is dispersed via the first sprinklers in a typical centre-pivot irrigation system. Surface water samples, as well as water from various pump stations used for irrigation, were collected over a period of three years at sampling sites along a 159 km stretch of the Vaal River. Sample analyses revealed that faecal coliforms were always present (7.19 x 105 CFU/100 ml). Also, 59 Fusarium isolates were obtained from the water, as well as eight Fusarium isolates from onion bulbs that were cultivated in fields irrigated by water from the river. Molecular identification revealed that the isolates belonged to four Fusarium species, i.e. Fusarium brachygibbosum, Fusarium incarnatum-equiseti, Fusarium solani and Fusarium oxysporum, the latter being the dominant species represented by 52 isolates. The pathogenicity of the Fusarium isolates was determined against onion bulbs (Lombardi cultivar), and it was found that none of the water isolates caused basal rot and were therefore not representatives of Focep. However, four F. oxysporum isolates obtained from the onion bulbs were found to be Focep belonging to the vegetative compatibility group (VCG) 0425, previously known to be prevalent in the Western Cape Province. Despite the fact that no pathogenicity toward onion could be confirmed among the waterborne Fusarium isolates, subsequent screening for virulence factors, i.e. SIX (secreted in xylem) genes, revealed the presence of the SIX7 gene in some isolates. These isolates may therefore be potentially pathogenic to crops other than onion cultivated in the Lower Vaal region. A concentration of 1.50 mg/L „HTH® Super Shock It‟ was discovered to effectively remove 100% of faecal coliforms within 16 s from the water, while Fusarium spores were removed at 7.50 mg/L after 3600 s. Thus, while the disinfectant may be ineffective at removing fungal plant pathogens from a centre-pivot irrigation system within the required time, the results indicate that it will remove coliform bacteria from the water before it is dispersed onto crops.