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Universität Hannover (1997)

Factors contributing to the distribution and incidence of aflatoxin producing fungi in stored maize in Benin

Hell, Kerstin

Titre : Factors contributing to the distribution and incidence of aflatoxin producing fungi in stored maize in Benin

Auteur : Hell, Kerstin

Université de soutenance : Universität Hannover

Grade : Doktors der Gartenbauwissenschaften ( Dr. rer. hort. ) 1997

The aim of this study was to get an indication about the importance of stored maize as a source for the health threatening contamination with mycotoxins, especially aflatoxins in Benin, West-Africa. Information was also gathered about the possible cause of high contamination levels and strategies to reduce these adverse effects were evaluated. The aflatoxin incidence of 300 farmers’ stores in four agroecological zones was evaluated over a two year period. At the time of sampling in the storage bins, a questionnaire was used to identify production, harvest and storage practices that had an effect on aflatoxin across agroecological zones. In 1993-94 A. flavus development in stored maize shortly after harvest was comparatively low, with 10 to 20% of the grains contaminated. Six months later it increased to over 55%. In 1994-95 the percentage of grains that showed A. flavus presence was between 8 to 47%. Over the survey period 25% of all the samples were aflatoxin positive and out of these samples 60% had levels of more than 20 ppb. There were several management practices that were positively related with aflatoxin contamination. Planting of maize in the same field consecutively, and in a crop rotation that incorporated crops that supported growth of A. flavus, increased the risk of contamination. Harvest practices associated with lower aflatoxin load were : harvest at maturity with the husk, drying outside the field without the husk, drying followed by sorting of damaged or spoilt cobs. Use of insecticides and smoking in storage reduced fungal contamination. Damage to maize, either biotic or man-made in the field, during harvest, or in storage had negative effects. Insects have long been implicated in the spread of Aspergillus spores and the development of aflatoxins. In this study a relationship was found between the presence of insects and aflatoxin.Damage due to the cob borer Mussidia nigrivinella, the nitidulid Carpophilus spp. and the maize weevil Sitophilus zeamais correlated with high aflatoxin incidence. In a trial, the influence of storage form on aflatoxin contamination was evaluated. Maize that was stored as grains showed the highest aflatoxin content. Storage types that increased the risk of fungal development are storage on the ceiling, on roof tops, in the Ago (used in the Northern Guinea Savanna) and in storage containers that were more than 5 years old. Farmers’ practices that were linked to lower aflatoxin contamination were : storage in either the Ago (made from bamboo) or use of jute or polyethylene bags as secondary stores.

Mots clés : Benin ; Körnermais ; Lagerung ; Aspergillus flavus ; Aflatoxin

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