Department of Plant Pathology

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Browsing Department of Plant Pathology by Subject "Aflatoxins"

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    Mycotoxin contamination of maize and groundnut produced by subsistence farmers in northern KwaZulu-Natal
    (Stellenbosch : Stellenbosch University, 2018-03) Phokane, Sylvia; Rose, Lindy J. ; Flett, B. C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Subsistence farmers in South Africa face many production challenges including infection of their grain crops with mycotoxigenic fungi and concomitant mycotoxin contamination. Fusarium spp. and Aspergillus spp. are the most common fungal species infecting maize and groundnuts while plant-parasitic nematodes are also associated with groundnuts in South Africa. Maize and groundnut questionnaires regarding production practices were presented to subsistence farmers in Pongola, Vryheid, Jozini, Manguzi and Mbazwana districts of northern KwaZulu-Natal (KZN), South Africa. Maize and groundnut grain samples were also collected at harvest and after three months of storage during the 2012/13 and 2013/14 seasons. Groundnuts, roots and soil samples were collected before harvest during the 2013/14 season, only. Fusarium graminearum, F. verticillioides and A. flavus target DNA levels were quantified in maize using quantitative polymerase chain reaction and the presence of multi-mycotoxins were determined using the liquid chromatography tandem mass spectrometry. Nematodes were extracted using sieving method and identified microscopically. Questionnaires revealed that over 90% of farmers were not aware of mycotoxins or their implications on human and livestock health. Visually diseased grain was often fed to livestock sensitive to mycotoxicosis such as chickens. Production practices amongst some farmers including crop rotation and the well-ventilated storage of grain may contribute to reduced mycotoxin contamination. In maize grain the Fusarium graminearum levels were significantly higher than F. verticillioides and A. flavus levels in both seasons. Contrary to expectations, zearalenone, produced by F. graminearum, was very low (<0.02 μg/g) at harvest and storage during both seasons while deoxynivalenol and nivalenol was not detected. There were significant differences between districts (localities) and collection periods (harvest and storage) and localities per seasons (P < 0.05) for all mycotoxigenic fungi and mycotoxins evaluated. Maize sampled in Jozini district was the most contaminated with mycotoxigenic fungi and mycotoxins while Mbazwana and Manguzi districts were the least contaminated. Four plant-parasitic nematodes, namely D. africanus, Pratylenchus spp., Meloidogyne spp. and Helicotylenchus spp., were identified from groundnut samples obtained in Jozini, Manguzi and Mbazwana during the 2012/13 and 2013/14 seasons. Furthermore, Tylenchus spp. was identified for the first time in groundnuts, pegs and soil collected before harvest during the 2013/14 season. Results from this study showed that there is a need for mycotoxin awareness campaigns and additional surveillance to continuously monitor mycotoxin contamination and potential exposure. More in-depth analyses of all the potential factors contributing to mycotoxin contamination and exposure, particularly in the subsistence production are of northern KZN, is warranted.
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    Mycotoxin levels in subsistence farming systems in South Africa
    (Stellenbosch : Stellenbosch University, 2008-03) Ncube, Edson; Waalwijk, C.; Flett, B. C.; Viljoen, Altus; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: Fusarium spp. and Aspergillus spp. are toxin-producing fungi associated with maize and groundnut. Fusarium verticillioides produces fumonisins in maize, and Aspergillus flavus produces aflatoxins in maize and groundnut kernels. Both toxins are responsible for carcinogenesis in humans and animals. Contamination of maize and groundnut with mycotoxins is often most severe in rural areas where subsistence farmers are unaware of their existence and follow agricultural practices that might contribute to their production. A questionnaire was, therefore, compiled to investigate agricultural decisions in rural areas that may influence mycotoxin contamination of crops. During 2006 and 2007, maize and groundnut samples were collected in the Eastern Cape, KwaZulu-Natal (KZN), Limpopo, and Mpumalanga provinces. Mycotoxin levels were quantified using the ELISA technique, and the incidence of Fusarium spp. in maize grain was determined by plating maize kernels out on Fusarium selective medium. Fumonisin-producing Fusarium spp. were also quantified using real-time PCR (TaqMan). The incidence of A. flavus and A. parasiticus in groundnut was determined by plating out kernels on potato dextrose agar. Fumonisin contamination levels in maize samples ranged from 0-21.8 parts per million (ppm) and aflatoxin levels ranged from 0- 49 parts per billion (ppb), depending on the region where samples were collected. Aflatoxin levels in groundnut ranged from 0-160.1 ppb. Fusarium verticillioides was the most common Fusarium sp. in maize followed by F. subglutinans and F. proliferatum, respectively. Regression analyses showed a positive correlation between fumonisin-producing Fusarium species when determined by real-time PCR and fumonisin concentration (r2=0.866). Regression analyses further showed a highly significant positive correlation between A. flavus and aflatoxin contamination (r2=0.10235). Samples from northern KZN contained levels of mycotoxins that were far in excess of the maximum levels set by the Food and Drug Administration in the USA. In South Africa there are currently no regulations with regard to the maximum allowable levels of fumonisin in human food. The high incidence of mycotoxin contamination of human food in subsistence farming systems indicates the need for awareness programmes and further research.