Thesis (MScAgric (Plant Pathology)--Stellenbosch University, 2008.
Includes bibliography.summary,list of figures and appendices. / 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. / AFRIKAANSE OPSOMMING:
Fusarium spp. en Aspergillus spp. is toksien-produserende fungi wat met mielies en
grondbone geassosieer word. Fusarium verticillioides produseer fumonisiene in mielies,
terwyl, A. flavus aflatoksiene in mielies en grondbone produseer. Beide toksiene is
karsinogenies vir mens en dier. Die vlakke van toksien-kontaminasie is meestal die ergste in
landelike gebiede waar bestaansboere onbewus is daarvan. Landboupraktyke wat deur die
boere toegepas word vererger dikwels die probleem. ‘n Vraelys is saamgestel om vas te stel
watter landboupraktyke in landelike gebiede toegepas word, en hoe dit toksien-kontaminasie
in mielies en grondbone beinvloed. In die 2006 en 2007 seisoene is mielie- en
grondboonmonsters in Kwa-Zulu-Natal (KZN), die Oos Kaap, Limpopo en die Mpumalanga
provinsie versamel. Toksien-vlakke is gekwantifiseer deur gebruik te maak van die ELISA
tegniek. Die insidensie van Fusarium spp. in mielies was bepaal deur pitte op Fusariumselektiewe
agar uit te plaat. Fumonisien-produserende Fusarium spp. was ook gekwantifiseer
deur van kwantitatiewe PCR (TaqMan) gebruik te maak. Die voorkoms van A. flavus en A.
parasiticus is bepaal deurdat mielie- en grondboonpitte op aartappel dekstrose agar uit te
plaat. Fumonisien-vlakke in die mieliemonsters het gewissel van 0-21.8 dele per miljoen
(dpm), terwyl aflatoksienvlakke gewissel het van 0-49 dele per biljoen (dpb), afhangende van
die omgewing waar monsters versamel is. Aflatoksien vlakke in die grondboonmonsters het
gewissel van 0-160.1 dpb. Fusarium verticillioides is die meeste vanuit mielies geisoleer,
gevolg deur F. subglutinans en F. proliferatum. Regressie analises het ‘n positiewe korrelasie
tussen fumonisien konsentrasie en fumonisien-produserende spp. aangedui waar daar gebruik
gemaak is van die kwantitatiewe PCR (r2= 0.866). Regressie analises het ‘n hoogs
betekenisvolle positiewe korrelasie getoon tussen A. flavus en aflatoksien kontaminasie
(r2=0.10). Monsters van noordelike KZN het toksienvlakke bevat ver bokant die maksimum
toelaatbare vlakke is soos bepaal deur die Food en Drug Administrasie in die Verenigde State
van Amerika. Daar is tans geen regulasies in Suid Afrika wat die maksimum toelaatbare
vlakke van fumonisiene in voedsel vir menslike gebruik bepaal nie. Die hoë voorkoms van
mikotoksien-kontaminasie in bestaansboer-sisteme, dui die belangrikheid van verdere
navorsing en bewusmakings-progamme aan.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/3801 |
| Date | 03 1900 |
| Creators | Ncube, Edson |
| Contributors | Waalwijk, C., Flett, B. C., Viljoen, A., Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 151 leaves : ill. |
| Rights | Stellenbosch University |
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