Distribution of Aspergillus Section Flavi among Field Soils from the Four Agroecological Zones of the Republic of Bénin, West Africa

Maize has been adopted as a primary staple human food in Africa. In parts of West Africa, it is consumed up to three times a day and is used as weaning food for babies (1,21). Maize is vulnerable to degradation by mycotoxic fungi, but in the developing world and in sub-Saharan Africa in particular, official monitoring of mycotoxin contamination levels is rare. In West Africa, 98% of people test serologically positive for aflatoxin exposure (32), and in Bénin Republic and Nigeria high concentrations of aflatoxins have been found in preand postharvest maize (15,27,30,31). Aflatoxin is one of the most potent natural toxins that people may consume without knowledge of potential health impacts (2,4). All aflatoxin producing fungi are contained within Aspergillus section Flavi. Fungal isolates within section Flavi vary widely in aflatoxin producing ability (10,13,17). Interest in this variability has increased because of recent suggestions that atoxigenic strains of A. flavus and A. parasiticus might be applied to agricultural fields in order to reduce the risk of aflatoxin contamination (5,9,12). The species most commonly implicated in contamination events, A. flavus, can be divided into two strains on the basis of morphological, physiological, and genetic criteria (3,7). Typical or L strain isolates vary widely in aflatoxin producing ability, and a significant percent of L strain isolates are atoxigenic (produce no aflatoxins). S strain isolates have a tendency to produce greater quantities of smaller sclerotia than L strain isolates. S strain isolates also produce more aflatoxin than L strain isolates, and atoxigenic S strain isolates are rare (7,10,17). The S strain has been further divided into SB isolates that produce only B aflatoxins and SBG isolates that produce both B and G aflatoxins (11,25). Initial comparison of S strain isolates from West Africa and North America revealed that only SB isolates occurred in North America, whereas in West Africa only SBG occurred (11,16). Description of the variability within Aspergillus section Flavi across the distinct agroecological zones of West Africa would facilitate efforts to define the etiology of aflatoxin contamination in that region. The current study looks at the distribution and toxigenicity of species and strains within Aspergillus section Flavi across four agroecological zones in Bénin Republic.