Browsing by Author "Wubet, Tesfaye"

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    Fusarium and Fusarium Toxins in Maize in Some Regions of Ethiopia.
    (Addis Ababa University, 1997-06) Wubet, Tesfaye; Abate Dawit (PhD)
    Maize Grain Samples Were Collected from stores and markets in Shashemene and Alemaya regions. Samples were rated as damaged, Hornlal and malted. Nannal and damaged samples were rated based on percentage of kernel discolouration, wrinkledness, floating ofke~le1s in water and attack by insects. Mycofloral study of the three sets of samples showed that the three tox.jgenic fungal genera: Fusarium, Aspergillus and Penicillium were COllunon in maize in Ethiopia. Among these toxigenic fungi Fusarium was the most common genus, comprising 17.5 % of the total fungi isolated and was recovered from 80.5 % of the samples investigated, Species of fusarium were most prevalent in damaged and malted samples than in nonnal samples. TIle ftmgus was represented in 91.7 % and 28 % of the total fungal isolates in damaged and malted samples respectively. In the normal samples, however, Aspergillus and Penicillium spp were more prevalent and they were represented in all the samples examined. Preliminary test result of screening toxigenic fusarium isolates using the brine shrimp (Artemia salina) bioassay showed that 93 % of them were tmdgenic. The frequently occurring toxigenic fusarium were identified to be Fusarium prolijeratum, Fusarium gramil1earum, Fusarium subglutillGns and Fusarium alllhophilum. Isolates of these frequent toxigenic species were grown on sterile shredded maize grain and their extracts were assayed for toxicity on the brine shrimp larvae. The results indicate production of methanol and/or chloroform soluble toxic metabolites. Bioassay directed isolation of toxic principles from chloroform extract of F. graminearum isolates showed production of zearalenonc and trichothecene compounds (TA and TB). Based on their physico· chemical data four compOlUlds that belong to the fumonisins were isolated from methanol extracts of F. proliferatum isolates. TIle results of the study on screening of toxigenic fusarium and bioassay directed isolatfon and purification of toxic principles indicated the importance of brine sluimp bioassay in screeuing toxigenic fusarium and detection of fusarium toxins. Toxicity assay results from extracts of selected grain samples of the three sets of samples indicated that 93 % of the tested sample extracts were toxic. In the natural occurrence study of the toxins, zearatenone and the trichothecenes (TA and TB) were detected in 50, 50, and 75 % of the damaged samples examined respectively. The estimated concentration ranges from 0-0.42 J.tglg for zearalenone, 0-1.5 J.tglg for TA and 0·2.3 J.tglg for TB. The fumonisins, on the other hand, were detected in all the samples examined with the highest concentrations in the malted and damaged samples. The results of this study showed that toxigenic fusarium are associated with maize samples and their toxins are fOlmd on the grain. TIle biological effect and thermostability of some of the toxins indicates the health hazard of consuming mould infected grains, particularly damaged and malted grains. This necessitates the quality control of maize grain destined for human consumption.